Blood test

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Blood tests are laboratory tests done on blood to gain an appreciation of disease states and the function of organs. Since blood flows throughout the body, acting as a medium for providing oxygen and other nutrients, and drawing waste products back to the excretory systems for disposal, the state of the bloodstream affects, or is affected by, many medical conditions. For these reasons, blood tests are the most commonly performed medical tests. Blood is obtained from one of the patient’s veins by venipuncture or fingerprick, except for tests such as Arterial blood gas.

Blood is useful as it is a relatively non-invasive way to obtain cells, and extracellular fluid (plasma), from the body to check on its health. Although the term blood test is used, most routine tests (except for most haematology) are done on plasma or serum.

The list below includes both specific tests, and general techniques.

Blood chemistry tests

A basic metabolic panel measures sodium, potassium, chloride, bicarbonate, blood urea nitrogen (BUN), magnesium, creatinine, and glucose. It also sometimes includes calcium.

While the regular glucose test is taken at a certain point in time, the glucose tolerance test involves repeated testing to determine the rate at which glucose is processed by the body.

While the above tests are all taken from venous blood, by contrast the arterial blood gas test is, as its name would suggest, taken from arterial blood, and is therefore more dangerous and uncomfortable.

Large organic molecules

Proteins

Protein electrophoresis (general technique — not a specific test)
Western blot (general technique — not a specific test)
Liver function tests

Antibody Proteins

Serology (general technique — not a specific test)
- Wassermann test (for syphilis)
ELISA test
Coombs test

Other

Polymerase chain reaction (DNA). DNA testing is today possible with even very small quantities of blood: this is commonly used in forensic science, but is now also part of the diagnostic process of many disorders.
Northern blot (RNA)

Cells

Full blood count (or “complete blood count”)
Hematocrit and MCV (“mean corpuscular volume”)
Erythrocyte sedimentation rate (ESR)
Cross-matching. Determination of blood type for blood transfusion or transplants
Blood cultures are commonly taken if infection is suspected. Positive cultures and resulting sensitivity results are often useful in guiding medical treatment.

External links

Cold autoantibody webpage on “health a to z”