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Renal tubular acidosis
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FEATURED BOOKS ON THE KIDNEYS & RENAL TUBULAR ACIDOSIS FROM BARNES & NOBLE.COM:
FIRST THINGS FIRST, WHAT IS ACIDOSIS?
Acidosis is a general term for a serious condition in which there is an increase in acid or a decrease in alkaline substances in the blood or tissues. Alkaline substances are the opposite of acids, meaning that they are not acidic. As a simple example, lemon juice is acidic and spring water is alkaline. The chemical, bicarbonate, is an example of an alkaline substance in the body.
WHAT IS RENAL TUBULAR ACIDOSIS?
Renal tubular acidosis (abbreviated RTA) is a syndrome in which the kidney tubules (see next section) are not able to adequately remove acids from the blood and release them into the urine. As a result, the blood becomes more acidic and the urine becomes less acidic.
WHAT ARE THE KIDNEYS AND THE KIDNEY TUBULES?
The kidneys are two organs located on each side of the spine that filter (remove) wastes from the blood. Blood enters the kidneys through the renal (kidney) arteries. Arteries are types of blood vessels that carry blood away from the heart. The renal artery takes blood into the smallest functioning unit of the kidney, known as a nephron. A nephron is made up of a glomerulus and a long structure called a tubule. The glomerulus filters the blood and releases it into the tubule. Each kidney is made up of over a million tubules.
The tubules help reabsorb some essential chemical components and allow others to flow back to the center of the kidney, which is known as the medulla. The medulla is essentially a holding area for fluid waste. From here, the waste products are sent out to the urine and released from the body. Although the functioning of the tubules is impaired in RTA, the functioning of the glomeruli is generally not affected much. This is not always the case, however.
WHAT IS THE DIFFERENCE BETWEEN DISTAL AND PROXIMAL TUBULES?
There are two main types of tubules in the kidneys – distal tubules and proximal tubules. Both types of tubules are responsible for removing acid from the blood and excreting it into the urine. However, more acid is released from the proximal tubules. The word “proximal” means “near.” As such, the proximal part of the tubules is located closer to the point where fluid and wastes from the blood enter. The word “distal” means distant. As such, the distal part of the tubules is relatively distant from the point where fluid and wastes from the blood enters.
There is a straight section of the proximal and distal tubule and a convoluted (twisted) part. The convoluted proximal tubule reabsorbs 80 to 85% of bicarbonate The loop of Henle reabsorbs another 5 to 10% of bicarbonate. The loop of Henle is a U-shaped part of the kidney tubules that extends through the center of the kidney from the end of the proximal convoluted tubule to the beginning of the distal convoluted tubule. An enzyme known as carbonic anyhdrase is found in the proximal tubule and is important for reabsorption of bicarbonate. An enzyme is a type of protein that helps produce chemical reactions in the body.
TELL ME MORE ABOUT ACID LEVELS IN THE BODY
Normally, the cells of the body use chemical reactions to carry out tasks such as repairing tissues and digesting food. The chemical reactions produce acids that go on to circulate in the blood. Too much acid in the body can impair many functions of the body. For example, too much acid can lead to impaired growth, kidney stones, worsening kidney failure, and bone disease. For this reason, healthy kidneys remove these acids from the blood and excrete them into the urine in an attempt to properly balance the chemicals in the body. A normal balance of acids and other chemicals is critical to the body’s functioning.
The level of acidity is measured by the pH (potential hydrogen) level, which reflects the concentration of hydrogen ions. An ion is an atom or a group of atoms that have an electric charge by gaining or losing one or more electrons. An atom is the smallest part of a substance that can exist alone or in combination with something else. An electron is a negatively charged particle that is smaller than an atom. The body tries to maintain a balance between positive and negatively charged particles.
A pH level of 7.0 is considered neutral, below 7.0 is acidic, and above 7.0 is alkaline (opposite of acidic). The normal pH balance of the body is very slightly alkaline (between 7.35 and 7.45). The normal pH is slightly alkaline because acidic substances in the body, such as carbon dioxide and molecules containing hydrogen, are made less acidic by the alkaline substances, the most common of which is known as bicarbonate. Molecules are the smallest naturally occurring particles of a substances and are made of any number of atoms, from one to thousands.
When the pH balance is not between 7.35 and 7.45, oblems will start since every other chemical in the body is affected by the balance of acids. The most important of these chemicals are oxygen, sodium (salt), chloride, potassium (a type of metallic element), calcium, ammonium, carbon dioxide, and phosphates.
The kidneys normally help to regulate the pH level of the body by ARE THERE DIFFERENT TYPES OF RENAL TUBULAR ACIDOSIS?
Yes. There are three different types of RTA, each of which produces their own signs and symptoms, although there is some overlap. The mechanism that causes the tubules to fail to make the urine more acidic differs in each type of RTA.
Despite the severely high level of acid in the blood in people with distal RTA, the pH balance of the urine is greater than 5.5 (normal is 7) because not as much acid is released into the urine. Remember that a pH balance less than 7 is acidic. Not everyone with distal RTA has severely high levels of acid in the blood, however. To learn how distal RTA can be diagnosed when this occurs, go to the diagnosis section of this entry.
Normally, the distal tubules will return potassium to the blood supply. This is important because potassium is important in regulating muscle health, nerve health, and heart rate. In distal RTA, this function is impaired and there is a loss of potassium in the urine. Severely low levels of potassium can cause extreme weakness, paralysis, decreased reflexes, abnormal heart rhythm, and even death. Paralysis is loss of movement and/or sensation. Although potassium levels in the blood are usually low in distal RTA, these levels can be normal in some cases.
In distal RTA, decreases in extracellular fluid result from renal sodium wasting. Extracellular fluid is fluid that exists outside of a cell. Extracellular fluid contains proteins and electrolytes. Renal sodium wasting is when the kidneys excrete very high levels of salt into the urine. Renal sodium wasting is common in distal RTA and leads to an increased loss of potassium in the urine and hyperaldosteronism.
Hyperaldosteronism is a disease caused by too much production of aldosterone. Alodosterone is a hormone responsible for maintaining sodium and potassium balance. Hormones are natural chemicals produced by the body and released into the blood that have a specific effect on tissues in the body. It should be noted that since potassium loss decreases the release of aldosterone, this often limits the severity of the hyperaldosteronism.
Since the defective proximal tubule cannot reabsorb bicarbonate, the excess bicarbonate goes to the distal tubule. The distal tubule becomes overwhelmed in attempting to reabsorb bicarbonate. This decreases the amount of hydrogen ions that are normally excreted into the urine by the distal tubules. Since there is less acid in the urine, not as much bicarbonate is needed there to neutralize it. Thus, bicarbonate levels in the urine also decline. In severe cases, there may be no bicarbonate in the urine. With less bicarbonate present, the urine becomes more acidic.
Increased delivery of sodium to the distal tubules can result in hyperaldosteronism and renal wasting (see above). Muscle weakness and decreased reflexes are common symptoms of proximal RTA. The symptoms are brought on by an increase of bicarbonate in the blood. Kidney stones and calcium formation in the kidneys do not occur in this type of RTA unlike in distal RTA. Proximal RTA is most common in infancy but is less common than distal RTA.
The acidosis in proximal RTA is usually not as high as in distal RTA. Unlike distal RTA, in proximal RTA there is greater than 15 milliequivalents of bicarbonate per liter of blood. The pH of the urine is less than 5.5, but is usually greater than 5.5 before proximal RTA becomes established. Levels of potassium are usually decreased in proximal RTA although they can be normal.
The increased hydrogen and potassium ions in the blood make it very acidic. Hyperkalemic RTA is often suspected when high potassium levels accompany high acid levels and low bicarbonate levels in the blood. The pH of the urine is less than 5.5, meaning that it is very acidic. The urine is acidic because the hydrogen ion pumps function normally and can release some hydrogen ions into the urine in response to the high levels of acid in the blood.
WHY IS THERE NO SUCH THING AS TYPE 3 RENAL TUBULAR ACIDOSIS IF THERE IS TYPE 1, 2, & 4?
The term “Type 3 renal tubular acidosis” is no longer used. What was once called Type 3 RTA is now considered a type of distal RTA in which there is leaking of bicarbonate from the proximal tubules and a defect of the distal tubules. Some consider Type 3 RTA to be a combination of Type 1 and Type 2 RTA.
ARE THERE INCOMPLETE FORMS OF RENAL TUBULAR ACIDOSIS?
Yes, there is an incomplete form of distal RTA. In this forms of RTA, the pH balance of the arterial blood is normal and acidosis can only be detected during the acid load test (see below). This condition can only be detected when the acid load is greater than the excretion of hydrogen ions.
WHAT CAUSES RENAL TUBULAR ACIDOSIS?
For convenience purposes, we have listed the causes of the main types of RTA by diving them into sections below.
A second cause of decreased hydrogen excretion is that the hydrogen ions flow back into the distal tubules, which is what happens in cases caused by the drug, amphotericin B. Amphotericin B is a type of drug used to treat infections caused by a fungus, which is a simple type of parasite. Amphoceterin B causes the formation of openings in the membrane of the distal tubules, which allows some of the hydrogen ions to flow back in.
A third cause of decreased proton excretion is low levels of sodium. Sodium is needed to help transport protons out of the distal tubules. Therefore, if sodium levels are low, not enough protons will be released. Sodium is normally reabsorbed into the kidneys. Any process that decreases sodium reabsorption can lead to problems secreting protons from the distal tubules. Levels of potassium (which is also a proton) may also increase because potassium secretion is also dependent on normal sodium levels.
A fourth cause of decreased proton excretion in the distal tubules is low availability of ammonium. Ammonium is a colorless alkaline gas with a strong odor. Low levels of ammonium can be caused by decreased production of this substance or poor reabsorption and transportation of it. Normally, hydrogen ions combine with ammonia to form a proton known as an ammonium ion. The ammonium ion then becomes trapped because it is now too large and must be excreted into the urine. Since the ammonium ion is alkaline, it would normally make the urine less acidic. If there is not enough ammonia present, however, not enough ammonium ions will be made. This means that not enough ammonium ions will go into the urine and it will become more acidic.
Distal RTA can occur alone or can be caused by diseases or disorders that affect various organs. A good example is the various autoimmune disorders. Autoimmune disorders are known causes of distal RTA. An autoimmune disorder is one in which a person's organs or tissues are mistakenly attacked by his/her immune system (defense system). Examples of autoimmune diseases that can cause distal RTA (see types) include systemic lupus erythematosus (abbreviated SLE), Sjogren’s syndrome, and Hashimoto thyroiditis.
SLE is a long-term disease in which the connective tissues throughout the body are inflamed because the body's defense system attacks these tissues as if they were foreign substances. Sjogren’s syndrome is a disease in which the eyes and mouth become excessively dry. Hashimoto thyroiditis is a disease in which the immune system attacks and destroys the thyroid gland. The thyroid gland is a butterfly-shaped organ located in the front of the neck that plays an important role in metabolism. Metabolism is the chemical actions in cells that release energy from nutrients or use energy to create other substances.
Disorders that result in calcium deposits in the kidneys can cause distal RTA. Examples of such disorders are hyperparathyroidism and vitamin D intoxication. Hyperparathyroidism is a disorder in which the parathyroid glands are overactive. The paratrhyroid glands are four small glands located on either side of the thyroid gland which regulate the level of calcium in the blood. Vitamin D is a very important vitamin that serves to maintain normal levels of calcium, but too much vitamin D results in increased calcium levels.
Distal RTA can be caused by certain drugs such as acetazolamide, amphotericin B (defined above), and lithium carbonate. Acetazolamide is used to treat glaucoma, a condition in which increased pressure in the eye can lead to gradual loss of vision. A parasite is an organism that lives in or on another organism to obtain nourishment. Lithium carbonate is a type of salt that is used as a drug to reduce mania (an abnormal, overly excited state).
Inhalation of toluene has been known to cause distal RTA. Toluene is a type of clear, colorless liquid used to make chemicals and explosives. Pain medications (known as analgesics) can lead to distal RTA through a process known as analgesic nephropathy. Analgesic neuropathy involves damage to one or both kidneys due to an overexposure to mixtures of medications, especially over-the-counter pain medications.
Rejection of a kidney transplant can also cause distal RTA as can long-lasting and/or recurring urinary tract infections. Obstructive uropathy can lead to distal RTA. Obstructive uropathy is blockage of the flow of urine from both kidneys, which can cause the backup of urine and kidney injury. Hereditary deafness, in which infants are deaf at birth, is associated with distal RTA.
Proximal (and distal) RTA can be inherited from dominant autosomal genes in the parents. In fact, researchers have discovered the abnormal gene responsible for the inherited form of distal RTA. This is the most common cause of RTA when it occurs in infants.
Genes are units of material contained in a person's cells that contain coded instructions as for how certain bodily characteristics (such as eye color) will develop. All of a person's genes come from his/her parents. Genes can either be dominant or recessive. A gene that masks the effect of another gene is called a dominant gene. The gene whose expression is masked is known as a recessive gene.
Genes are contained in structures called chromosomes. Each person has 23 pairs of chromosomes, meaning that there are 46 chromosomes in total. One of each pair of chromosomes is inherited from the mother and one of each pair is inherited from the father. The first 22 pairs of chromosomes (known as autosomes) are not involved in determining sex. The 23rd pair of chromosomes, however, is involved in determining sex. Thus, an autosomal gene is a gene from one of the first 22 pairs of chromosomes.
Other possible causes of distal RTA include vitamin D deficiency, kidney damage due to disease, and illegal drug use. Another cause of distal RTA is increased amounts of calcium in the urine. Calcium is a natural element that is very important in bone formation. Heavy metal poisoning has been known to cause proximal RTA. Proximal RTA is associated with a failure to thrive. Failure to thrive is a term used for infants that describes abnormally slowed growth and development resulting from conditions that interfere with normal appetite, activity, and metabolism.
Proximal RTA can also be caused by medullary cystic disease. Medullary cystic disease is a hereditary disorder where the kidneys gradually lose their ability to function because of cysts in the medulla (center) of each kidney. A cyst is an abnormal lump, swelling, or sac that contains fluid, a part solid material, or a gas, and is covered with a membrane. A membrane is a thin layer of flexible tissue that covers something.
Cystinosis is a known cause of proximal RTA. Cystinosis is a disease characterized by an abnormal accumulation of the amino acid, cystine, in various organs of the body such as the kidneys, eyes, and brain. Lead nephropathy, which is lead poisoning of the kidneys can also lead to proximal RTA. Another cause or proximal RTA is amyloidosis. Amyloidosis is a general term for a collection of diseases that result in the abnormal deposition of amyloid protein throughout the body. Amyloid protein is a starchy type of protein that causes damage when present in abnormally high amounts.
Proximal RTA has been known to be caused by a cancer drug known as ifosfamide (Mitoxana). A few older medications, such as older tetracycline or acetazolamide can cause RTA. Tetracycline is a medication used to treat infections. Acetazolamide is a medication used to treat glaucoma (see last section on distal RTA).
Proximal RTA can be inherited from dominant autosomal genes in the parents. This is the most common cause of RTA when it occurs in infants. See the previous section on causes of distal RTA for a discussion of genes. There are numerous inherited conditions that are associated with proximal RTA such as hereditary fructose intolerance, Lowe’s syndrome, Fanconi’s syndrome, and Wilson’s disease.
Hereditary fructose intolerance is an inherited disorder in which the body is not able to metabolize fructose (a type of sugar), which results in a buildup of fructose in the kidneys, liver, and small intestine. The liver is the largest organ in the body and is responsible for filtering (removing) harmful chemical substances, producing important chemicals for the body, and other important functions. The intestine is divided into two main sections: the small intestine and the large intestine. The small intestine takes in all of the nutrients (healthy substances) that the body needs.
Lowe’s syndrome is a rare inherited condition that causes physical and mental handicaps such as visual impairment, poor muscle development, mental retardation, seizures, severe behavioral problems, kidney problems, and short stature. Fanconi’s syndrome, which occurs most often in children, is an impairment in the functioning of the proximal tubule of the kidney. Wilson’s syndrome is a rare inherited disorder in which copper accumulates slowly in the liver and is taken up by other parts of the body.
There are various medications that can lead to low levels of aldosterone. On example is a type of medication that decreases inflammation, known as non-steroidal anti-inflammatories (abbreviated as NSAIDs). An example of an NSAID is aspirin. Another type of medication that decreases aldosterone is heparin, which prevents blood from clotting. Medications to treat congestive heart failure, known as diuretics (such as spironolactone or eplerenone), can lower aldosterone levels. Congestive heart failure is an imbalance in the pumping action of the heart that causes inadequate blood circulation. The condition is associated with increased fluid buildup around the heart. Diuretics are types of medications that decrease fluid buildup.
There are other medications that lower aldosterone levels such as trimethoprim, which is a type of antiobiotic. Another antibiotic, known as pentamidine, can decrease aldosterone levels. Pentamidine is used to treat pneumonia. Pneumonia is inflammation of the lungs due to infection. Some drugs that decrease the effectiveness on the body’s immune system (defense system) to prevent rejection of transplanted tissue can cause low aldosterone levels. These type of medications are known as immunosuppressive drugs. Medications that treat high blood pressure, known as angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARBs) can lower aldosterone levels.
Hyperkalemic RTA is also associated with autoimmune diseases and blockages of the urinary tract. The urinary tract is the part of the body that deals with the formation and excretion of urine. Hyperkalemic RTA is can also be caused by kidney transplantation or amyloidosis. Amyloidosis is a general term for a collection of diseases that result in the abnormal deposition of amyloid protein throughout the body. Amyloid protein is a starchy type of protein that causes damage when present in abnormally high amounts.
Hyperkalemic RTA is also associated with diabetes mellitus and sickle cell anemia. Diabetes mellitus (often abbreviated as DM) is a complex, long-term disorder in which the body is not able to effectively use a natural chemical called insulin. Insulin's main job is to quickly absorb glucose (a type of sugar) from the blood into cells or their energy needs and into the fat and liver (a large organ that performs many chemical tasks) cells for storage.
Sickle cell anemia is a disease in which the red blood cells become sickle shaped, which leads to joint pain, fever, weakness, and anemia. Anemia is a condition in which there is an abnormally low amount of hemoglobin in the blood. Hemoglobin is substance present in red blood cells that help carry oxygen to cells in the body. Red blood cells help carry oxygen in the blood.
Hyperkalemic RTA can occur with Addison’s disease or following bilateral adrenalectomy. Addison's disease is a life-threatening condition in which there is a complete or partial failure of the adrenal cortex. The adrenal cortex is the outer part of an important organ (the adrenal gland) that produces hormones essential for the body to regulate itself. A bilateral adrenalectomy is the surgical removal of both adrenal glands.
WHAT ARE THE SIGNS AND SYMPTOMS OF RENAL TUBULAR ACIDOSIS?
Signs and symptoms of RTA vary depending on what is causing the problem and how the chemicals in the body readjust to compensate for it. Some signs and symptoms include tiredness, confusion, weakness, decreased alertness, decreased reflexes, increased breathing rate, increased heart rate, muscle cramps, muscle pain, bone pain, back pain, stomach pain, nausea, vomiting, constipation, slowed growth in children, persistent dehydration (an excessive loss of water from body tissues), bloody urine, decreased or increased urine output, and loss of appetite resulting in the inability to eat.
Dehydration may occur because water accompanies the release of many of the molecules that are excreted in RTA. The dehydration tends to be mild. Breathing rate can be increased in RTA because of the body’s attempt to decrease high carbon dioxide levels. The high carbon dioxide levels occur as a result of increased bicarbonate levels. Remember that when people breathe, they release carbon dioxide into the air.
Low levels of potassium in the blood (as is seen in Type 1 & Type 2 RTA) can affect the nerves of the body and cause symptoms such as extreme weakness, abnormal heart rhythms, decreased reflexes, paralysis, and even death. High levels of potassium in the blood (as is seen in type 4 RTA) typically does not cause symptoms. However, if potassium levels become high enough paralysis can develop, as can an irregular heartbeat.
High acid levels can cause calcium to dissolve from the bones, causing them to soften. Calcium is the most abundant mineral in the body. The calcium that is lost from the bones can then build up in the blood and be released by the kidneys as waste. This is why many people with RTA have high levels of calcium in the urine. The loss of calcium can then cause bone deformities (such as rickets), impaired growth in children, and muscle weakness. Rickets is a condition in which abnormal bone formation is caused by a deficiency of calcium and vitamin D. And speaking of calcium, RTA can also cause calcium formation of the kidney and kidney stones. Impaired growth is particularly likely to occur in children if distal RTA goes untreated. If untreated in adults, distal RTA can lead to worsening kidney disease and bone disease.
RTA causes low levels of bicarbonate in the blood and high levels of chloride. Chloride is a combination of the element, chlorine, with another element. Chloride is a negatively charged ion that is produced in excess by the body to balance out excess positively charged ions. High levels of chloride are present in all types of RTA.
The anion gap in people with RTA is typically normal. Anion gap is a measurement of the anions in the arterial blood besides chloride and bicarbonate anions. Anions are ions with a negative electric charge. Ions are atoms or a group of atoms that have an electric charge by gaining or losing one or more electrons. An atom is the smallest part of a substance that can exist alone or in combination with something else. An electron is a negatively charged particle that is smaller than an atom. The anion gap can be high in cases where there is significantly decreased functioning of the glomeruli (the main filtering units of the kidneys), but this does not happen often.
RTA can cause infections of the urinary tract. The urinary tract is the part of the body that deals with the formation and release of urine from the body as waste. RTA can also cause pyelonephritis, which is a widespread, pus-producing infection of the pelvis and functional kidney tissue. The pelvis is a massive bone made of hip bones on each side and the front, while the back part is made of the sacrum (a triangular bone) and coccyx (a beak shaped bone).
Hyperkalemic RTA rarely causes symptoms unless potassium levels become so high as to cause irregular heartbeat or muscle paralysis. Most patients with hyperkalemic RTA have kidney failure that is associated with disorders affecting the kidney tubules and the blood vessels inside the kidney (known as the renal interstitium). Hyperkalemic RTA is associated with increased rennin activity. Renin is an enzyme released in the blood by the kidney in response to stress.
WHAT ARE EMERGENCY SIGNS AND SYMPTOMS OF RENAL TUBULAR ACIDOSIS?
Emergency symptoms include severe decreases in alertness and orientation, decreased consciousness, and seizures. Seizures are involuntary muscle movements and/or decreased awareness of the environment due to overexcitement of nerve cells in the brain. Anyone who has such symptoms should seek immediate medical assistance.
HOW IS RENAL TUBULAR ACIDOSIS DIAGNOSED?
RTA is diagnosed based on the nature of the reported symptoms in addition to blood and urine tests. The laboratory tests will look for too much acid in the blood, too little potassium in the blood, and too little acid in the urine. These tests are known as blood pH and urine pH tests. The urine pH test may show a decreased level of hydrogen ions. If these tests indicate RTA is present, additional information about sodium, potassium, and chloride in the blood will help the doctor determine what type of RTA is present.
A test known as an arterial blood gas (ABG) is commonly used to test the acid level in the blood. During this test, an injection is made into an artery so samples of gases can be removed an analyzed in the lab. An artery is a type of blood vessel that carries blood away from the heart.
If a low pH balance is found in the blood, this means the blood is too acidic.
In distal RTA, the pH balance of the urine is typically greater than 5.5. Remember that a pH balance less than 7 is acidic. A urine pH balance greater than 5.5 in the presence of acidic blood levels is usually diagnostic of distal RTA. However, the following condition must be ruled out before such a diagnosis is made: urinary tract infections, low potassium levels, and sodium retention. Urinary tract infections can raise the pH level of the urine. Low levels of potassium can cause increased ammonia production, which will then lead to increased urine pH since ammonia is an alkaline substance.
The presence of kidney stones is additional evidence for a diagnosis of distal RTA. This is because distal RTA is the only type of RTA where kidney stones are present. Kidney stones can damage the cells of the kidney, leading to long-term kidney failure in the worst case scenario.
Laboratory tests are used to confirm cases of proximal RTA by showing that bicarbonate wasting is due to impaired bicarbonate reabsorption. Bicarbonate levels in the urine are often assessed with a measure known as the fractional excretion of bicarbonate. This is commonly abbreviated as FE-HCO3. FE stands for fractional excretion and HCO3 is the chemical abbreviation for bicarbonate. In this test, bicarbonate is given to the patient until a prespecified level is reached. When half of that level is reached, the fractional excretion of bicarbonate increases to 15% in patients with proximal RTA. In patients without proximal RTA, the FE-HCO3 level will remain at less than 5%, indicating good bicarbonate reabsorption.
The fractional excretion of bicarbonate is calculated by multiplying the amount of bicarbonate in the urine by the amount of creatinine in the blood and dividing that number by the amount of bicarbonate in the blood multiplied by the creatinine in the urine. If that sounds confusing, the actual calculation is as follows: bicarbonate in the urine x creatinine in the blood/ bicarbonate in the blood x creatinine in the urine. Creatinine is a waste product of the normal breakdown of muscle during activity. The test assumes that blood levels of bicarbonate are normal. Thus, this test is used as a measure of bicarbonate in the urine, taking into account the level of creatinine.
Other significant laboratory findings include decreased levels of bicarbonate in the blood, decreased or increased potassium, and decreased phosphorous. Phosphorous is a type of nonmetallic chemical element that is important for the body’s metabolism. Blood tests may also find increased levels of chloride and bicarbonate in the blood. High levels of alkaline phosphatase can be found in the urine. Alkaline phosphatase is a type of enzyme found in all tissues. An enzyme is a type of protein that helps produce chemical reactions in the body.
Analysis of the urine may show that it is non-acidic. However, this may change over time as the blood becomes more acidic and increasing amounts of bicarbonate are reabsorbed to counteract the acidic condition. Decreased levels of glucose (a type of sugar) and amino acids may also be found when the urine is analyzed because the kidneys are not working as well to filter these substances. Amino acids are a group of chemical substances that form proteins. Lab tests may also show that the urine has a high specific gravity, meaning that it is very dense or concentrated.
Another useful diagnostic tool is to measure the amount of ammonium in the urine. Although some laboratories are equipped to do this, others are not. This is why a calculation has been created to estimate the amount of ammonium. The calculation involves subtracting the amount of chlorine in the urine from the combined amount of sodium and potassium in the urine. The result of the calculation is known as the urine net charge.
If there is a high amount of ammonium ions in the urine, the amount of chloride will be far higher than the sum of the sodium and potassium amounts. Chloride has a negative electric charge and its levels are increased to balance out the extra positive charge of the ammonium ions. The more ammonium that is present, the higher the chloride levels will need to be to balance it. Therefore, if there is too much ammonium in the urine, the urine net charge will be negative because there are more negative chloride ions than positive sodium and positive potassium ions.
Since there is no defect in ammonium production in proximal RTA, the urine net charge will be negative. However, in distal RTA, there can be a defect in ammonium production. If this happens, there will be less ammonium released into the urine. With less ammonium, there is less chloride made to counteract its electrical charge. This means that the positive electrical charge of the sodium and potassium will be greater than the negative electrical charge of the chloride. For this reason, a positive urine net excretion indicates the presence of distal RTA.
As was mentioned earlier, not all people with distal RTA have high levels of acid in the blood. In order to diagnose distal RTA in people with lower than severe levels of acid in the blood, tests need to be done in which the acid level is raised artificially. This is known as an acid loading test.
In an acid loading test, the patient takes capsules of ammonium chloride three days prior to a blood or urine sample being taken. Ammonium chloride is a colorless and odorless type of salt that should make the blood slightly more acidic when introduced. The samples of blood and urine will be analyzed in the laboratory. If the level of bicarbonate in the blood drops but the pH balance of the urine remains greater than 5.5, the diagnosis of distal RTA is made.
HOW IS RENAL TUBULAR ACIDOSIS TREATED?
The first goal in treating RTA is to decrease acid levels in the blood. Normal pH balance and electrolyte levels need to be restored. In children, a major goal is restoring normal growth. More specific treatment will be geared towards treating the type of RTA one has. For example, in distal RTA, a goal will be to decrease kidney stone formation. The underlying cause of acquired RTA should obviously be treated if it can be identified.
Distal and proximal RTA are treated by drinking a daily mixture of water and bicarbonate (baking soda) to neutralize the acid produced by food. Bicarbonate tablets are also available. Treating RTA with alkaline substances is known as alkaline treatment.
Alkaline treatment can relieve symptoms or keep them from worsening. For example, it can restore normal growth patterns, prevent bone disease, kidney stones, kidney failure, loss of sodium (salt), and leakage of calcium into the urine. In distal RTA, alkaline treatment helps correct the common problem of too much sodium being excreted into the urine. By doing this, it helps restore the extracellular fluid levels to normal and increases the amount of potassium in the blood.
The dose of bicarbonate that is given is usually large because too much bicarbonate is leaving the body through the urine. For distal RTA, the dose is about 1 to 4 millequivalents per kilogram of body weight per day. For proximal RTA, the dose is about 2 to 15 millequivalents per kilogram of body weight per day. For hyperkalemic RTA, the dose is about 2-3 millequivalents per kilogram of body weight per day. A milliequivalent is a very small unit of weight that is about one thousandth of a gram. To understand how small a gram is, you need about 453 grams just to get one pound. A kilogram is 1000 grams. Sodium citrate is another alkalaine substance that can be given to reduce acid. The goal is to get the patient’s level of bicarbonate in the blood to greater than 22 milliequivalents per liter.
Potassium loss increases in patients who receive bicarbonate treatment. For this reason, a potassium supplement (potassium citrate) may also be prescribed to make the blood less acidic. However, this step is rarely needed. Potassium citrate and salt supplements can be very useful if there is too little potassium in the blood. Potassium citrate also helps to bind calcium together so it will help prevent kidney stones from forming.
Patients with low levels of potassium in the blood will likely be asked to eat foods rich in potassium, such and oranges, bananas, and baked potatoes. Thus, as one can see, in distal and proximal RTA, treatment involves replacing substances that are excessively released by the body.
Other substances besides potassium and bicarbonate may need to be replaced.
For example, vitamin D and calcium supplements may be necessary to reduce possible bone deformities from RTA. Vitamin D may also be given to preserve calcium metabolism, meaning that the body will be able to use calcium for the functions it normally provides in the body. If pyelonephritis develops (see above), antibiotic may be prescribed. Surgery may be needed if kidney stones develop.
The high potassium levels in hyperkalemic RTA can often be treated by decreasing potassium intake and if necessary, taking diuretics. Diuretics are medications that help reduce fluid buildup in the body. Reducing the fluid in the body helps the body reabsorb bicarbonate. Thiazide diuretics are types of diuretics that may be given to help the body reabsorb bicarbonate and promote the release of potassium from the body. Thiazide diuretics are diuretics that are commonly used to treat high blood pressure. Although some cases of proximal RTA may go away without treatment, this condition is generally treated to reduce symptoms and complications (see above), which can be permanent and life threatening.
WHAT IS THE PROGNOSIS FOR PEOPLE WITH RENAL TUBULAR ACIDOSIS?
If treated early, most people with RTA will not develop permanent kidney failure. The longer the condition goes untreated, however, the greater the likelihood of permanent kidney failure. Therefore, the goal is to recognize and diagnose the disease early and to treat it adequately. The patient will need to be treated and monitored throughout his/her lifetime. People with distal RTA tend to respond better to alkaline treatment than those with proximal RTA.
ARE THERE SPECIAL NURSING CONSIDERATIONS FOR PATIENTS WITH RTA?
Yes. Nurses monitor the patient’s blood and urine laboratory results carefully to check for any abnormal values. Potassium levels and the acidity level (pH) of the blood are especially important values to look at. Nurses strain the patient’s urine to look for kidney stones and blood in the urine. Adults with multiple myeloma need to be carefully monitored since distal RTA can complicate the course of this illness. Multiple myeloma is cancer of the bone marrow. Bone marrow is a tissue that fills the center of long bones.
WHAT IS THE PROGNOSIS FOR PEOPLE WITH RENAL TUBULAR ACIDOSIS?
The prognosis for people with RTA is usually good given that one is able to carefully balance the level of chemicals in his/her body. However, the prognosis for a specific individual will depend on the extent of kidney damage and the type of treatment. As was mentioned earlier, cases of proximal RTA may go away by itself without treatment.
CAN RENAL TUBULAR ACIDOSIS BE PREVENTED?
Generally not. Most disorders that cause RTA are not preventable. However, doctors generally recommend that relatives of patients with inherited forms of RTA be tested to see if they have it.
WHAT ELSE IS RENAL TUBULAR ACIDOSIS KNOWN AS?
Renal tubular acidosis is also known as hyperchloremic acidosis.
WHAT IS THE ORIGIN OF THE TERM, RENAL TUBULAR ACIDOSIS?
Renal tubular acidosis comes from the Latin word “ren” meaning “kidney,” the Latin word “tubulus” meaning “little tube,” the Latin word “acidus” meaning “sour, ”and the Greek word “ososi” meaning “condition.” Put the words together and you have “sour condition (of the) little tubes (of the) kidney.”
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