TESTS: BLOOD CHEMISTRY TESTS

A blood chemistry profile consists of a number of tests that measure the levels of certain chemical substances in blood serum (the liquid part of the blood). Abnormal blood chemistry test results may, but not always, indicate a health problem, and normal test results can occur in people who have a medical disorder. If you have an abnormal test result, your doctor will order another blood test to see if the results are consistent before recommending further medical tests. The ranges given for normal results can vary slightly from laboratory to laboratory.

Cholesterol and Lipids

A cholesterol and lipids test measures the levels of various fats in the blood, including triclycerides; HDL (high-density lipoprotein), the good cholesterol; and LDL (low-density lipoprotein), the bad cholesterol. Increased levels of triglycerides or LDL cholesterol and decreased levels of HDL cholesterol can indicate an increased risk of cardiovascular disease, including heart disease, atherosclerosis and stroke. Doctors use the cholesterol test to evaluate heart disease risk. Drugs such as corticosteroids, thiazide diuretics and oral contraceptives can affect cholesterol levels. Excess alcohol intake, kidney and liver diseases, obesity, menopause, diabetes, and hypothyroidism (underactive thyroid) can also affect cholesterol and lipid levels.

Measuring Cholesterol Levels
Beginning at age 20, you should have a cholesterol test at least every five years, and more frequently if you have a family history of heart disease. The numbers provided on your cholesterol profile can help your doctor evaluate your risk of developing heart disease. Your risk of heart disease is low if your total cholesterol level is less than 200 milligrams per deciliter (mg/dL), your LDL (bad) cholesterol level is below 100 mg/dL, your HDL (good) cholesterol level is higher than 40 mg/dL, and your triglyceride level is less than 150 mg/dL. The measurement is most reliable when performed after you have fasted for 12 hours.

Glucose

Glucose is a sugar that the body uses for energy. The hormone insulin, which is produced by the pancreas, regulates the level of glucose in the blood. Increased levels of glucose can be a sign of diabetes. Decreased levels of glucose can be a sign of adrenal insufficiency (underfunctioning of the adrenal glands). Conditions such as a stroke or heart attack can temporarily increase glucose levels. Medications such as corticosteroids, diuretics and tricyclic antidepressants can also increase glucose levels. In general, low blood sugar is a rare condition in people who are otherwise healthy. The normal glucose range is 65 to 109 milligrams per deciliter (mg/dL).

Albumin

The albumin test measures the amount in the blood of the protein albumin, which keeps water inside blood vessels and is the most plentiful protein in the body. The albumin level is a good indicator of a person's general nutritional status. Disorders such as hepatitis, cirrhosis, and malnutrition can cause a decrease in the level of albumin. The level of albumin is also decreased during pregnancy. The test can help diagnose liver disease, kidney disease, and intestinal disorders, such as Crohn's disease, that can reduce the absorption of nutrients. People who have cancer or chronic diseases such as autoimmune disorders or AIDS often have a low albumin level. The normal albumin range is 3.7 to 5.2 grams per deciliter (g/dL).

Alkaline Phosphatase

Alkaline phosphatase (ALP) is an enzyme that is present in all tissues of the body. High concentrations of ALP are normally found in the liver, in bile ducts, in bone, and, in pregnant women, in the placenta. Extremely high levels of ALP can be a sign of several abnormal conditions, including bone disease, leukemia and liver disease. The enzyme can also be elevated in normal conditions such as healthy bone growth or result from an abnormal response to a medication. The normal ALP range is 40 to 157 international units per liter (IU/L).

Alanine Aminotransferase

Alanine aminotransferase (ALT) is an enzyme found in many tissues, but is present in high levels in the liver. Doctors use the ALT test to detect liver damage, which can cause ALT to be released into the blood. Extremely high levels of ALT can be a sign of liver diseases such as hepatitis and cirrhosis. The normal ALT range is 5 to 35 international units per liter (IU/L).

Aspartate Aminotransferase

Aspartate aminotransferase (AST) is an enzyme found mostly in the heart muscle, skeletal muscle cells and liver cells. Conditions such as liver disease, infectious mononucleosis and muscle disease can increase the level of AST in the blood. Recent surgery, exercise and pregnancy can also raise levels of AST. Doctors use the AST test mainly to diagnose or monitor liver disease and, occasionally, to monitor people who have had a heart attack. The normal AST range is 10 to 34 international units per liter (IU/L).

Blood Urea Nitrogen

Blood urea nitrogen (BUN) is a by-product of the breakdown of proteins in the liver. An elevated BUN level can be a sign of kidney disease or, occasionally, severe gastrointestinal bleeding. Medications such as antibiotics and diuretics can also affect BUN levels. Doctors use the BUN test to evaluate kidney function and to diagnose conditions such as gastrointestinal bleeding. The normal BUN range is 8 to 23 milligrams per deciliter (mg/dL).

Calcium

The serum calcium test measures the amount of calcium in blood serum. Increased levels of calcium can be a sign of cancer that has spread to the bones from another part of the body, multiple myeloma, hyperthyroidism (an overactive thyroid gland), or hyperparathyroidism (overactive parathyroid glands). Medications such as lithium, thiazide diuretics and antacids can also increase the levels of calcium in the blood. Doctors use the serum calcium test to diagnose or monitor conditions such as bone disease, kidney disease, endocrine diseases and cancer. A low calcium level can result from severe, acute pancreatitis. The normal total calcium range is 8.4 to 10.3 milligrams per deciliter (mg/dL).

Carbon Dioxide

Carbon dioxide is a waste product of normal metabolism. The lungs eliminate carbon dioxide from the blood through breathing. Increased levels of carbon dioxide can indicate disorders that affect the lungs, such as emphysema or other obstructive lung diseases, or loss of stomach acid from vomiting. Drugs such as corticosteroids and excessive use of antacids can also increase the blood levels of carbon dioxide. Decreased levels of carbon dioxide can result from severe, uncontrolled diabetes, kidney failure or severe diarrhea. The normal carbon dioxide range is 21.3 to 30.3 milliequivalents per liter (mEq/L).

Creatinine

Creatinine is a muscle enzyme that is present in the blood in various levels based on a person's size and muscle mass and that is filtered out by the kidneys and excreted in urine. Doctors measure the levels of creatinine to diagnose kidney diseases. The normal creatinine range is 0.6 to 1.1 milligrams per deciliter (mg/dL).

Total Bilirubin

Bilirubin is an orange-yellow pigment in bile, a liquid secreted by the liver to remove waste products and break down fats during digestion. Doctors use the total bilirubin test to diagnose liver disease, jaundice (yellowing of the skin and the whites of the eyes), and obstruction of the bile duct (the tube that carries bile from the liver). The normal total bilirubin range is 0.2 to 1.1 milligrams per deciliter (mg/dL).

Direct Bilirubin

The direct bilirubin test measures the blood level of a form of bilirubin called conjugated bilirubin. The blood usually contains very small amounts of conjugated bilirubin. However, damage to the liver can increase the amount of bilirubin in the blood. The normal direct bilirubin range is 0.04 to 0.20 milligram per deciliter (mg/dL).

Indirect Bilirubin

An elevated level of indirect (unconjugated) bilirubin can be a sign of conditions such as hemolytic anemia, pernicious anemia, and neonatal jaundice. The normal indirect bilirubin range is 0.2 to 0.7 milligram per deciliter (mg/dL).

Gamma Glutamyltransferase

Gamma glutamyltransferase (GGT) is an enzyme that is usually found at high levels in the kidneys, liver, and bile ducts. Doctors use the GGT test to help diagnose disorders of the liver, bile ducts, and gallbladder, which can increase the levels of GGT. Use of some drugs such as phenobarbital and excessive intake of alcohol can increase GGT levels. The normal GGT range is 0 to 51 international units per liter (IU/L).

Lactate Dehydrogenase

Lactate dehydrogenase (LDH) is an enzyme found in many tissues, especially the brain, heart, liver, kidneys, lungs, blood cells and skeletal muscles. Doctors use the LDH test to detect tissue damage. Increased levels of LDH may be a sign of a heart attack, liver disease, lung problems or advanced cancer. Drugs such as aspirin and some anesthetics and narcotics can also increase LDH levels. The normal LDH range is 105 to 333 international units per liter (IU/L).

Phosphorus

Phosphorus is a substance that the body uses, along with calcium, for bone development and growth. Increased levels of phosphorus in the blood can be a sign of kidney failure and hypoparathyroidism (underactive parathyroid glands). The normal serum phosphorus range is 2.4 to 4.4 milligrams per deciliter (mg/dL).

Potassium

Potassium is a mineral that is essential for maintaining nerve impulses, water balance in the body, normal heart rhythm and muscle function. Increased levels of potassium in the blood can be a sign of kidney failure and can occur when a person is undergoing hemodialysis (a treatment for kidney failure in which a machine temporarily performs the functions of the kidneys). Decreased levels of potassium can result from fluid loss such as from excessive sweating, vomiting or diarrhea. Medications such as angiotensin-converting enzyme (ACE) inhibitors can increase the level of potassium in the blood. Medications such as laxatives, insulin or salicylates can decrease the amount of potassium in the blood. The normal potassium range is 3.5 to 5.3 milliequivalents per liter (mEq/L).

Sodium

Sodium is a chemical that plays an important part in maintaining the balance of water and salt in the body. Some hormones can cause a loss of sodium. Increased levels of sodium can indicate excessive loss of water (dehydration). Eating too many salty foods and not drinking enough water can also increase sodium levels. Decreased levels of sodium can be a sign of kidney disease, severe brain disease, or lung disease. Medications such as diuretics and some medications used for treating diabetes can also decrease sodium levels. The normal sodium range is 133 to 145 milliequivalents per liter (mEq/L).

Total Protein

Doctors measure the overall level of protein in the blood to detect a variety of diseases including liver diseases, kidney diseases and a blood cancer called multiple myeloma. Medications such as corticosteroids, insulin and growth hormone can increase protein levels in the blood. Medications such as the hormone estrogen can decrease protein levels. The normal total protein range is 6 to 8 grams per deciliter (g/dL).

Uric Acid

Uric acid is a by-product of metabolism that is normally excreted by the kidneys in urine. An increase in the amount of uric acid can be a sign of gout, kidney failure or lead poisoning. Drugs such as alcohol, diuretics and caffeine can increase the amount of uric acid in the blood. The normal uric acid range is 2.6 to 7.8 milligrams per decilter (mg/dL).

Excerpted from: Family Medical Guide, Fourth Edition, American Medical Association, 2004.