Clinical chemistry uses chemical processes to measure levels of chemical components in body fluids. The most common specimens tested in clinical chemistry are blood and urine. Many different tests exist to test for almost any type of chemical component in blood or urine. Components may include blood glucose, electrolytes, enzymes, hormones, lipids (fats), other metabolic substances, and proteins.
The following is a description of some of the most common clinical chemistry tests (used on blood and urine specimens), including some of the uses and indications:
Blood glucose, or blood sugar, levels indicate how the body handles glucose. Measuring glucose levels after fasting (when the patient has not eaten anything for 8 hours) can help diagnose diabetes or hypoglycemia (low blood sugar).
Electrolytes include sodium, potassium, chloride, bicarbonate, calcium, phosphorus, and magnesium. Measuring electrolytes can specifically indicate certain metabolic and kidney disorders.
Enzymes are released into the blood by organs that are damaged or diseased. The type of enzyme released can indicate which organ is affected:
Can signal damage to heart muscle or skeletal muscle
CK-MB, an isoenzyme of CK, is used to distinguish heart muscle damage
Alanine aminotransferase (ALT, SGPT), aspartate aminotransferase (AST, SGOT)
Can signal liver disorders
Amylase and lipase
Can signal inflammation or the possibility of cancer of the pancreas
Hormones are secreted by the various endocrine glands to regulate the processes of the body. Raised or lowered levels of certain hormones can indicate over- or under-activity of those glands:
Thyroxine (T4), TSH
FSH, ACTH, growth hormones
Lipids are fatty substances such as triglycerides (body fat), phospholipids (part of cell membranes), and sterols (such as cholesterol). Lipids can help signal coronary heart disease and liver disease:
High total cholesterol is a risk factor for cardiovascular disease (CVD)
High-density lipoprotein (HDL or "good" cholesterol)
Low-density lipoprotein (LDL or "bad" cholesterol)
High LDL cholesterol is also a risk factor for CVD
High HDL cholesterol is a protective factor against CVD
High triglycerides are another independent risk factor for CVD
Other metabolic substances can be measured to evaluate organ function:
BUN (blood urea nitrogen)
Can signal gout, kidney disease, and other tissue damage
Proteins can indicate metabolic and nutritional disorders, as well as certain cancers:
Total protein and albumin
Can signal liver or kidney disease, or malnutrition
Globulins and the A/G ratio (albumin to globulin)
Can signal infection, autoimmune disease, inflammation, and certain blood cancers
Often, abnormal blood and urine tests are repeated to make sure there is not a sample error or lab error. Abnormal tests are often followed up by other more specialized tests.