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BioChemistry

Biochemistry tests measure the chemical substances carried by the blood. Key tests indicate the level of functioning of the liver and kidneys. They also measure the levels of fats and sugar circulating the body in certain age and gender determined populations, PSA (Prostate Specific Antigen) and TSH (Thyroid Stimulating Hormone) tests are done to evaluate the functioning of the Prostate and Thyroid glands respectively.

RENAL PROFILE

UREA

The blood urea nitrogen or BUN test is primarily used, along with the creatinine test, to evaluate kidney function in a wide range of circumstances, to help diagnose kidney disease, and to monitor people with acute or chronic kidney dysfunction or failure. It also may be used to evaluate a person's general health status when ordered as part of a basic metabolic panel (BMP) or comprehensive metabolic panel (CMP).

Creatinine : How is it used?

The creatinine blood test is used along with a BUN (blood urea nitrogen) test to assess kidney function. Both are frequently ordered as part of a basic or comprehensive metabolic panel (BMP or CMP), groups of tests that are performed to evaluate the function of the body’s major organs. BMP or CMP tests are used to screen healthy people during routine physical exams and to help evaluate acutely or chronically ill people in the emergency room and/or hospital. If the creatinine and BUN tests are found to be abnormal or if someone has an underlying disease, such as diabetes, that is known to affect the kidneys, then these two tests may be used to monitor the progress of kidney dysfunction and the effectiveness of treatment. Blood creatinine and BUN tests may also be ordered to evaluate kidney function prior to some procedures, such as a CT (computed tomography) scan, that may require the use of drugs that can damage the kidneys.
A combination of blood and urine creatinine levels may be used to calculate a creatinine clearance. This test measures how effectively the kidneys are filtering small molecules like creatinine out of the blood.
Urine creatinine may also be used with a variety of other urine tests as a correction factor. Since it is produced and removed at a relatively constant rate, the amount of urine creatinine can be compared to the amount of another substance being measured. This stable excretion rate is useful when evaluating both 24-hour urine samples and random urine samples. Examples of this are when creatinine is measured with protein to calculate a urine protein/creatinine ratio (UP/CR) and when it is measured with microalbumin to calculate a microalbumin/creatinine ratio.
The microalbumin/creatinine ratio is calculated to help determine how much albumin is escaping from the kidneys into the urine. People who have consistently detectable amounts of albumin in their urine (microalbuminuria) have an increased risk of developing progressive kidney failure and cardiovascular disease in the future.
Serum creatinine measurements (along with age, weight, and gender) also are used to calculate the estimated glomerular filtration rate (eGFR), which is used as a screening test to look for evidence of kidney damage.

SODIUM

Blood sodium testing is used to detect abnormal concentrations of sodium, termed hyponatremia (low sodium) andhypernatremia (high sodium). A doctor may order this test, along with other electrolytes, to identify an electrolyte imbalance. It may be ordered to determine if a disease or condition involving the brain, lungs, liver, heart, kidney, thyroid, or adrenal glands is causing or being exacerbated by a sodium deficiency or excess. In patients with a known electrolyte imbalance, a blood sodium test may be ordered at regular intervals to monitor the effectiveness of treatment. It may also be ordered to monitor patients taking medications that can affect sodium levels, such as diuretics.

Urine sodium levels are typically tested in patients who have abnormal blood sodium levels to help determine whether an imbalance is from, for example, taking in too much sodium or losing too much sodium. Urine sodium testing is also used to see if a person with high blood pressure is eating too much salt. It is often used in persons with abnormal kidney tests to help the doctor determine the cause of kidney damage, which can help guide treatment.

POTASSIUM

Potassium testing is frequently ordered, along with other electrolytes, as part of a routine physical. It is used to detect concentrations that are too high (hyperkalemia) or too low (hypokalemia). The most common cause of hyperkalemia iskidney disease, but many drugs can decrease potassium excretion from the body and result in this condition. Hypokalemia can occur if someone has diarrhea and vomiting or if is sweating excessively. Potassium can be lost through the kidneys in urine; in rare cases, potassium may be low because someone is not getting enough in their diet.

The potassium test may be ordered at regular intervals to monitor effects of drugs that can cause the kidneys to lose potassium, particularly diuretics. Monitoring may also be done if someone has a condition or disease, such as acute orchronic kidney failure, that can be associated with abnormal potassium levels.

CHLORIDE

Blood chloride testing is often ordered, along with other electrolytes, as part of a regular physical to screen for a variety of conditions. These tests may also be ordered to help diagnose the cause of signs and symptoms such as prolonged vomiting, diarrhea, weakness, and respiratory distress. If an electrolyte imbalance is detected, the doctor will look for and address the disease, condition, or medication causing the imbalance and may order electrolyte testing at regular intervals to monitor the effectiveness of treatment. If an acid-base imbalance is suspected, the doctor may also order blood gas tests to further evaluate the severity and cause of the imbalance.

In persons with too much base, urine chloride measurements can tell the doctor whether the cause is loss of salt (in cases of dehydration, vomiting, or use of diuretics, where urine chloride would be very low) or an excess of certainhormones such as cortisol or aldosterone (that can affect electrolyte excretion). Urine tests for chloride are also used, along with sodium, to monitor persons put on a low-salt diet. If sodium and chloride levels are high, the doctor knows that the patient is not following the diet.

URIC ACID

The uric acid blood test is used to detect high levels of this compound in the blood in order to help diagnose gout. The test is also used to monitor uric acid levels in people undergoing chemotherapy or radiation treatment. Rapid cell turnover from such treatment can result in an increase in uric acid.

The uric acid urine test is used to help diagnose the cause of recurrent kidney stones and to monitor people with gout for stone formation.

ALBUMIN

Since albumin is low in many different diseases and disorders, albumin testing is used in a variety of settings to help diagnose disease, to monitor changes in health status with treatment or with disease progression, and as a screen that may indicate the need for other kinds of testing.

An albumin test may be ordered as part of a liver panel to evaluate liver function, along with a creatinine and BUN (Blood Urea Nitrogen) to evaluate kidney function, or along with a prealbumin to evaluate a person's nutritional status.

URIC ACID

The uric acid blood test is used to detect high levels of this compound in the blood in order to help diagnose gout. The test is also used to monitor uric acid levels in people undergoing chemotherapy or radiation treatment. Rapid cell turnover from such treatment can result in an increase in uric acid.

The uric acid urine test is used to help diagnose the cause of recurrent kidney stones and to monitor people with gout for stone formation.

LIPID PROFILE

TRIGLYCERIDE

Blood tests for triglycerides are usually part of a lipid profile used to identify the risk of developing heart disease. As part of a lipid profile, it may be used to monitor those who have risk factors for heart disease, those who have had a heart attack, or those who are being treated for high lipid and/or high triglyceride levels.
Some risk factors for heart disease include:
• Cigarette smoking • Age (men 45 years or older or women 55 years or older) • Hypertension (blood pressure of 140/90 or higher or taking high blood pressure medications) • Family history of premature heart disease (heart disease in an immediate family member—male relative under age 55 or female relative under age 65) • Diabetes mellitus
If you are diabetic, it is especially important to have triglycerides measured as part of any lipid testing since triglycerides increase significantly when blood sugar levels are not well-controlled.

TOTAL CHOLESTROL

Cholesterol is different from most tests in that it is not used to diagnose or monitor a disease but is used to estimate risk of developing a disease — specifically heart disease. Because high blood cholesterol has been associated with hardening of the arteries (atherosclerosis), heart disease, and a raised risk of death from heart attacks, cholesterol testing is considered a routine part of preventive health care.

HDL – CHOLESTROL

The test for HDL cholesterol (HDL-C) is used along with other lipid tests to screen for unhealthy levels of lipids and to determine your risk of developing heart disease.

Your HDL-C level may also be monitored by your doctor on a regular basis if previous test results have shown you to have an increased risk for heart disease or if you have had a heart attack or if you are undergoing treatment for high cholesterol levels.

LDL – CHOLESTROL

The test for LDL cholesterol is used to predict your risk of developing heart disease. Of all the forms of cholesterol in the blood, the LDL cholesterol is considered the most important form in determining risk of heart disease. Since treatment decisions are often based on LDL values, this test may be used to monitor levels after the start of diet or exercise programs or to determine whether or not prescribing one of the lipid-lowering drugs would be useful.

LIVER PROFILE

ALBUMIN

Since albumin is low in many different diseases and disorders, albumin testing is used in a variety of settings to help diagnose disease, to monitor changes in health status with treatment or with disease progression, and as a screen that may indicate the need for other kinds of testing.

An albumin test may be ordered as part of a liver panel to evaluate liver function, along with a creatinine and BUN (Blood Urea Nitrogen) to evaluate kidney function, or along with a prealbumin to evaluate a person's nutritional status.

ALKALINE PHOSPHATASE

The alkaline phosphatase test (ALP) is used to help detect liver disease or bone disorders. In conditions affecting the liver, damaged liver cells release increased amounts of ALP into the blood. This test is often used to detect blocked bile ducts because ALP is especially high in the edges of cells that join to form bile ducts. If one or more of them are obstructed, for example by a tumor, then blood levels of ALP will often be high.
Any condition that affects bone growth or causes increased activity of bone cells can affect ALP levels in the blood. An ALP test may be used, for example, to detect cancers that have spread to the bone or to help diagnose Paget's disease. This test may also sometimes be used to monitor treatment of Paget's disease or other bone conditions, such as vitamin D deficiency. If ALP results are increased but it is not clear whether this is due to liver or bone disease, then tests for ALP isoenzyme tests may be done to determine the cause. A GGT test and/or a test for 5'-nucleotidase may also be done to differentiate between liver and bone disease. GGT and 5'-nucleotidase levels are increased in liver disease but not bone disorders.

AST (SGOT)

The blood test for aspartate aminotransferase (AST) is usually used to detect liver damage. It is often ordered in conjunction with another liver enzyme, alanine aminotransferase (ALT), or as part of a liver panel to screen for and/or help diagnose liver disorders. AST and ALT are considered to be two of the most important tests to detect liver injury, although ALT is more specific than AST. Sometimes AST is compared directly to ALT and an AST/ALT ratio is calculated. This ratio may be used to distinguish between different causes of liver damage.
AST levels are often compared with results of other tests, such as alkaline phosphatase (ALP), total protein, and bilirubinto help determine which form of liver disease is present.
AST is often measured to monitor treatment of persons with liver disease and may be ordered either by itself or along with other tests for this purpose.
Sometimes AST may be used to monitor people who are taking medications that are potentially toxic to the liver. If AST levels increase, then the person may be switched to another medication.

ALT (SGPT)

The alanine aminotransferase (ALT) blood test is typically used to detect liver injury. It is often ordered in conjunction withaspartate aminotransferase (AST) or as part of a liver panel to screen for and/or help diagnose liver disease. AST and ALT are considered to be two of the most important tests to detect liver injury, although ALT is more specific than AST. Sometimes AST is compared directly to ALT and an AST/ALT ratio is calculated. This ratio may be used to distinguish between different causes of liver damage.
ALT values are often compared to the results of other tests such as alkaline phosphatase (ALP), total protein, and bilirubinto help determine which form of liver disease is present.
ALT is often used to monitor the treatment of persons who have liver disease, to see if the treatment is working, and may be ordered either by itself or along with other tests for this purpose.

GGT

Gamma-glutamyl transferase (GGT) levels may be used to determine the cause of an elevated alkaline phosphatase (ALP). Both ALP and GGT are elevated in disease of the bile ducts and in some liver diseases, but only ALP will be elevated in bone disease. If the GGT level is normal in a person with a high ALP, the cause is most likely bone disease.
The GGT test is sometimes used to help detect liver disease and bile duct obstructions. It is usually ordered in conjunction with or as follow up to other liver tests such as ALT, AST, ALP, and bilirubin. Increased levels of GGT levels may indicate in general that the liver is being damaged but does not specifically point to a condition that may be causing the injury. While elevated GGT levels may be caused by liver disease, they may also be caused by alcohol consumption and/or other conditions, such as congestive heart failure. GGT can be used to screen for chronic alcohol abuse (it will be elevated in about 75% of chronic drinkers). Sometimes it may be used to monitor for alcohol use and/or abuse in people who are receiving treatment for alcoholism or alcoholic hepatitis.

TOTAL PROTEIN

Total protein measurements can reflect nutritional status and may be used to screen for and help diagnose kidney disease, liver disease, and many other conditions. Sometimes conditions are first detected with routine testing before symptoms have begun to appear. If total protein is abnormal, further tests must be performed to identify which specific protein is abnormally low or high so that a specific diagnosis can be made.

TOTAL BILIRUBIN

In adults and older children, bilirubin is measured to diagnose and/or monitor liver diseases, such as cirrhosis, hepatitis, or gallstones. It is also used to evaluate people with sickle cell disease or other causes of hemolytic anemia who may have episodes when excessive red blood cell destruction takes place, increasing bilirubin levels. Bilirubin can be measured as a total level and/or as conjugated and unconjugated levels for these purposes. More commonly, the laboratory uses a chemical test to detect water-soluble forms of bilirubin, termed direct bilirubin, which is an estimate of the amount of conjugated bilirubin. By subtracting this from the total bilirubin, an indirect estimate (indirect bilirubin) of unconjugated bilirubin is obtained.

In newborns with jaundice, bilirubin is measured to investigate the cause. Excessive unconjugated bilirubin damages developing brain cells in infants and may cause mental retardation, learning and developmental disabilities, hearing loss, or eye movement problems. It is important that an elevated level of bilirubin in a newborn be identified and quickly treated. In both physiologic jaundice of the newborn and hemolytic disease of the newborn, only unconjugated (indirect) bilirubin is increased. In the much less common cases of damage to the liver (neonatal hepatitis and biliary atresia), conjugated (direct) bilirubin elevations are present as well, often providing the first evidence that one of these less common conditions is present.

TOTAL PROTEIN

Total protein measurements can reflect nutritional status and may be used to screen for and help diagnose kidney disease, liver disease, and many other conditions. Sometimes conditions are first detected with routine testing before symptoms have begun to appear. If total protein is abnormal, further tests must be performed to identify which specific protein is abnormally low or high so that a specific diagnosis can be made.

DIRECT BILURUBIN

In adults and older children, bilirubin is measured to diagnose and/or monitor liver diseases, such as cirrhosis, hepatitis, or gallstones. It is also used to evaluate people with sickle cell disease or other causes of hemolytic anemia who may have episodes when excessive red blood cell destruction takes place, increasing bilirubin levels. Bilirubin can be measured as a total level and/or as conjugated and unconjugated levels for these purposes. More commonly, the laboratory uses a chemical test to detect water-soluble forms of bilirubin, termed direct bilirubin, which is an estimate of the amount of conjugated bilirubin. By subtracting this from the total bilirubin, an indirect estimate (indirect bilirubin) of unconjugated bilirubin is obtained.

In newborns with jaundice, bilirubin is measured to investigate the cause. Excessive unconjugated bilirubin damages developing brain cells in infants and may cause mental retardation, learning and developmental disabilities, hearing loss, or eye movement problems. It is important that an elevated level of bilirubin in a newborn be identified and quickly treated. In both physiologic jaundice of the newborn and hemolytic disease of the newborn, only unconjugated (indirect) bilirubin is increased. In the much less common cases of damage to the liver (neonatal hepatitis and biliary atresia), conjugated (direct) bilirubin elevations are present as well, often providing the first evidence that one of these less common conditions is present.

BONE PROFILE

CALCIUM

A blood calcium test is ordered to screen for, diagnose, and monitor a range of conditions relating to the bones, heart, nerves, kidneys, and teeth. Blood calcium levels do not directly tell how much calcium is in the bones, but rather, how much calcium is circulating in the blood.

A total calcium level is often measured as part of a routine health screening. It is included in the Comprehensive Metabolic Panel (CMP) and the Basic Metabolic Panel (BMP), groups of tests that are performed together to diagnose or monitor a variety of conditions. When an abnormal total calcium result is obtained, it is viewed as an indicator of an underlying problem. To help diagnose the underlying problem, additional tests are often done to measure ionized calcium, urine calcium, phosphorous, magnesium, vitamin D, and parathyroid hormone (PTH). PTH and vitamin D are responsible for maintaining calcium concentrations in the blood within a narrow range of values.

Measuring calcium and PTH together can help determine whether the parathyroid glands are functioning normally. Measuring urine calcium can help determine whether the kidneys are excreting the proper amount of calcium and testing for vitamin D, phosphorus, and/or magnesium can help determine whether other deficiencies or excesses exist. Frequently, the balance among these different substances, and the changes in them, are just as important as the concentrations.

Calcium can be used as a diagnostic test if a person has symptoms that suggest:
• Kidney stones • Bone disease • Neurologic disorders
The total calcium test is the test most frequently ordered to evaluate calcium status. In most cases, it is a good reflection of the amount of free calcium present in the blood since the balance between free and bound is usually stable and predictable. However, in some people, the balance between bound and free calcium is disturbed and total calcium is not a good reflection of calcium status. In these circumstances, the measurement of ionized calcium may be necessary. Some conditions where ionized calcium should be the test of choice include: critically ill patients who are receiving blood transfusions or intravenous fluids, patients undergoing major surgery, and patients with blood protein abnormalities like low albumin.

Large fluctuations in ionized calcium can cause the heart to slow down or to beat too rapidly, can cause muscles to go into spasm (tetany), and can cause confusion or even coma. In those who are critically ill, it can be extremely important to monitor the ionized calcium level in order to be able to treat and prevent serious complications.

PHOSPHORUS

Phosphorus tests are most often ordered along with other tests, such as those for calcium, parathyroid hormone (PTH), and/or vitamin D, to help diagnose and/or monitor treatment of various conditions that cause calcium and phosphorus imbalances.

While phosphorus tests are most commonly performed on blood samples, phosphorus is sometimes measured in urine samples to monitor elimination by the kidneys.

ALP

The alkaline phosphatase test (ALP) is used to help detect liver disease or bone disorders. In conditions affecting the liver, damaged liver cells release increased amounts of ALP into the blood. This test is often used to detect blocked bile ducts because ALP is especially high in the edges of cells that join to form bile ducts. If one or more of them are obstructed, for example by a tumor, then blood levels of ALP will often be high.

Any condition that affects bone growth or causes increased activity of bone cells can affect ALP levels in the blood. An ALP test may be used, for example, to detect cancers that have spread to the bone or to help diagnose Paget's disease. This test may also sometimes be used to monitor treatment of Paget's disease or other bone conditions, such as vitamin D deficiency.

If ALP results are increased but it is not clear whether this is due to liver or bone disease, then tests for ALP isoenzyme tests may be done to determine the cause. A GGT test and/or a test for 5'-nucleotidase may also be done to differentiate between liver and bone disease. GGT and 5'-nucleotidase levels are increased in liver disease but not bone disorders.

ALBUMIN

Since albumin is low in many different diseases and disorders, albumin testing is used in a variety of settings to help diagnose disease, to monitor changes in health status with treatment or with disease progression, and as a screen that may indicate the need for other kinds of testing.

An albumin test may be ordered as part of a liver panel to evaluate liver function, along with a creatinine and BUN (Blood Urea Nitrogen) to evaluate kidney function, or along with a prealbumin to evaluate a person's nutritional status.

VITAMIN D-25 OH

25-hydroxyvitamin D is used to determine if bone weakness, bone malformation, or abnormal metabolism of calcium (reflected by abnormal calcium, phosphorus, PTH) is occurring as a result of a deficiency or excess of vitamin D.

Since vitamin D is a fat-soluble vitamin and is absorbed from the intestine like a fat, vitamin D is sometimes used to monitor individuals with diseases that interfere with fat absorption, such as cystic fibrosis and Crohn's disease, and in patients who have had gastric bypass surgery and may not be able to absorb enough Vitamin D. Vitamin D is sometimes used to determine effectiveness of treatment when vitamin D, calcium, phosphorus, and/or magnesium supplementation is prescribed.

ANAEMIA PROFILE

IRON

Serum iron and a total iron-binding capacity (TIBC), or sometimes a UIBC (unsaturated iron-binding capacity) or transferrin test, are ordered together, and a transferrin saturation calculated to determine how much iron is being carried in the blood. A ferritin test may also be ordered to evaluate a person's current iron stores.

These tests are used together to detect and help diagnose iron deficiency or iron overload. In people with anemia, these tests can help determine whether the condition is due to iron deficiency or another cause, such as chronic illness. Iron tests are also ordered if a doctor suspects that a person has iron poisoning and to screen for hereditary hemochromatosis, an inherited condition associated with excessive iron storage.

TIBC

Total iron-binding capacity (TIBC) is most frequently used along with a serum iron test to evaluate people suspected of having either iron deficiency or iron overload. These two tests are used to calculate the transferrin saturation, a more useful indicator of iron status than just iron or TIBC alone. In healthy people, about 20-40% of available sites in transferrin are used to transport iron.

In iron deficiency, the iron level is low, but the TIBC is increased, thus transferrin saturation becomes very low. In iron overload states, such as hemochromatosis, the iron level will be high and the TIBC will be low or normal, causing the transferrin saturation to increase. UIBC may be ordered as an alternative to TIBC.

It is customary to test for transferrin (instead of TIBC or UIBC) when evaluating a patient's nutritional status or liver function. Because it is made in the liver, transferrin will be low in patients with liver disease. Transferrin levels also drop when there is not enough protein in the diet, so this test can be used to monitor nutrition.

FERRITIN

The ferritin test is ordered to assess a person's iron stores in the body. The test is sometimes ordered along with an iron test and a TIBC to detect the presence and evaluate the severity of an iron deficiency or overload.

FOLIC ACID

Vitamin B12 and folate are primarily ordered to detect deficiencies and to help diagnose the cause of certain anemias. One type of associated anemia is pernicious anemia, an autoimmune disease that affects the absorption of B12. This megaloblastic anemia occurs when the body produces antibodies against the gastric parietal cells or the intrinsic factor, resulting in B12 malabsorption.

Folate, B12, and an assortment of other tests may be ordered to help evaluate the general health and nutritional status of a person with signs of significant malnutrition or dietary malabsorption. This may include people with alcoholism, other liver diseases, gastric cancer, and those with malabsorption conditions such as celiac disease, tropical sprue, Crohn disease,inflammatory bowel disease, and cystic fibrosis.

B12 and folate may also be ordered to aid in diagnosis when an individual presents with an altered mental state or other behavioral changes, especially in the elderly. B12 may be ordered with folate, by itself, or with other screening laboratory tests (antinuclear antibody, CRP, rheumatoid factor, CBC and chemistry blood tests) to help establish reasons why a person shows symptoms of neuropathy. In those treated for known B12 and folate deficiencies, these tests will be ordered occasionally to monitor the effectiveness of treatment. This is especially true in those who cannot properly absorb B12 and/or folate and must have lifelong treatment.

Serum folate levels can vary based on dietary intake. RBCs can store 95% of circulating folate, thus a RBC folate level may be used to help detect a deficiency. Some doctors feel that the RBC folate test is more clinically relevant than serum folate, but there is not widespread agreement on this.

Other laboratory tests that make be useful are homocysteine and methymelonic acid (MMA). Homocysteine and MMA are elevated in B12 deficiency while only homocysteine is elevated in folate deficiency. This distinction is important because treating a B12-deficient patient with folate can correct the anemia but does not stop irreversible neurologic damage.

VITAMIN B12

Vitamin B12 and folate are primarily ordered to detect deficiencies and to help diagnose the cause of certain anemias. One type of associated anemia is pernicious anemia, an autoimmune disease that affects the absorption of B12. This megaloblastic anemia occurs when the body produces antibodies against the gastric parietal cells or the intrinsic factor, resulting in B12 malabsorption.

Folate, B12, and an assortment of other tests may be ordered to help evaluate the general health and nutritional status of a person with signs of significant malnutrition or dietary malabsorption. This may include people with alcoholism, other liver diseases, gastric cancer, and those with malabsorption conditions such as celiac disease, tropical sprue, Crohn disease,inflammatory bowel disease, and cystic fibrosis.

B12 and folate may also be ordered to aid in diagnosis when an individual presents with an altered mental state or other behavioral changes, especially in the elderly. B12 may be ordered with folate, by itself, or with other screening laboratory tests (antinuclear antibody, CRP, rheumatoid factor, CBC and chemistry blood tests) to help establish reasons why a person shows symptoms of neuropathy. In those treated for known B12 and folate deficiencies, these tests will be ordered occasionally to monitor the effectiveness of treatment. This is especially true in those who cannot properly absorb B12 and/or folate and must have lifelong treatment.

Serum folate levels can vary based on dietary intake. RBCs can store 95% of circulating folate, thus a RBC folate level may be used to help detect a deficiency. Some doctors feel that the RBC folate test is more clinically relevant than serum folate, but there is not widespread agreement on this.

Other laboratory tests that make be useful are homocysteine and methymelonic acid (MMA). Homocysteine and MMA are elevated in B12 deficiency while only homocysteine is elevated in folate deficiency. This distinction is important because treating a B12-deficient patient with folate can correct the anemia but does not stop irreversible neurologic damage.

CARDIAC PROFILE

HOMOCYSTEINE

A physician may order a homocysteine test to determine if a person has B12 or folate deficiency. The homocysteine concentration may be elevated before B12 and folate tests are abnormal. Some doctors may recommend homocysteine testing in malnourished patients, the elderly, who often absorb less vitamin B12 from their diets, and those with drug or alcohol addictions. A doctor may order both a urine and blood homocysteine to help diagnose homocystinuria if she suspects that an infant may have this inherited disorder. In some states, babies are tested for excess methionine as part of their newborn screening. If a baby's test is positive, then urine and blood homocysteine tests are often performed to confirm the findings.

Homocysteine may also be ordered as part of a screen for people at high risk for heart attack or stroke. It may be useful in someone who has a family history of coronary artery disease but no other known risk factors. Its utility for this purpose, however, continues to be questioned because the role, if any, that homocysteine plays in the progression of cardiovascular disease (CVD) has not been established. Routine screening, such as that done for total cholesterol, is not yet recommended.

CK

Blood levels of CK rise when muscle or heart cells are injured. Your doctor may test for CK if you have chest pain or othersigns and symptoms of a heart attack. In the first 4 to 6 hours after a heart attack, the concentration of CK in blood begins to rise. It reaches its highest level in 18 to 24 hours and returns to normal within 2 to 3 days. The amount of CK in blood also rises when skeletal muscles are damaged.

CKMB

CK–MB levels, along with total CK, are tested in persons who have chest pain to diagnose whether they have had a heart attack. Since a high total CK could indicate damage to either the heart or other muscles, CK–MB helps to distinguish between these two sources.

If your doctor thinks that you have had a heart attack and gives you a “clot-dissolving” drug, CK–MB can help your doctor tell if the drug worked. When the clot dissolves, CK–MB tends to rise and fall faster. By measuring CK–MB in blood several times, your doctor can usually tell whether the drug has been effective.

TROPONIN I

Troponin tests are primarily ordered to evaluate people who have chest pain to see if they have had a heart attack or other damage to their heart. Either a cardiac-specific troponin I or troponin T test can be performed; usually a laboratory will offer one test or the other. Troponin tests are sometimes ordered along with other cardiac biomarkers, such as CK–MB ormyoglobin. However, troponins are the preferred tests for a suspected heart attack because they are more specific for heart injury than other tests (which may become positive in skeletal muscle injury) and remain elevated for a longer period of time.

The troponin test is used to help diagnose a heart attack, to detect and evaluate mild to severe heart injury, and to distinguish chest pain that may be due to other causes. In those who experience heart-related chest pain, discomfort, or other symptoms and do not seek medical attention for a day or more, the troponin test will still be positive if the symptoms are due to heart damage.

MYOGLOBIN

Myoglobin may be ordered as a cardiac biomarker, along with troponin, to help diagnose or rule out a heart attack. Levels of myoglobin start to rise within 2-3 hours of a heart attack or other muscle injury, reach their highest levels within 8-12 hours, and generally fall back to normal within one day. An increase in myoglobin is detectable sooner than troponin, but it is not as specific for heart damage and it will not stay elevated as long as troponin.