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 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.
Specific biochemical blood tests include:
Hematological tests include:
Blood cultures are commonly taken if infection is suspected. Positive cultures and resulting sensitivity results are often useful in guiding medical treatment.
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.
Serology are blood tests that are often used to diagnose sexually transmitted diseases. Some jurisdictions insist on blood tests before marriage. Many states also require blood tests for all newborn babies.