blood tests
The definitions used in this glossary of terminology either have been provided by the authors of the articles, or have been extracted wholly or in part, or paraphrased from the following sources: The American Medical Association Encyclopedia of Medicine, Charles B. Clayman, MD, Medical Editor, Random House, New York, 1989; Biotechnology from A to Z, 2d Edition, William Bains, Oxford University Press, New York, New York, 2002; A Dictionary of Genetics, 6th Edition, Robert C. King and William D. Stansfield, Oxford University Press, New York, New York, 2002; Dorland's Illustrated Medical Dictionary, 29th and 30th Editions, W. B. Saunders Company, Philadelphia, 2000, 2003; Genes VII, Benjamin Lewin, Oxford University Press, New York, New York, 2000; The Gale Encyclopedia of Genetic Disorders, Volumes I and II, Stacey L. Blachford, Ed., Thomson Learning, New York, New York, 2002; The Merriam-Webster Dictionary, Merriam-Webster, Inc., Springfield, Massachusetts, 1997; Molecular Biology of the Cell, 3rd Edition, Bruce Alberts, et al., Garland Publishing, 1994; The Random House Dictionary of the English Language, Unabridged Edition, 1966; Webster's Ninth New Collegiate Dictionary, 1991.
DEFINITION:
- blood tests
-
Analysis of a sample of blood that gives information on its cells and proteins and any of the chemicals, antigens, antibodies, and gases that it carries. Since blood is the main transport system of the body, such tests can be used to check on the health of major organs, as well as on respiratory function, hormonal balance, the immune system, and metabolism.
Types
There are three types of blood tests.
Hematological Tests: These tests involve looking at the components of the blood itself, examining the numbers, shape, size, and appearance of cells, and testing the function of clotting factors. The most important hematological tests are blood count, blood smear, and blood clotting tests.
Biochemical Tests: These look at chemicals in the blood, such as sodium, potassium, uric acid, and urea, and at vitamins, gases, digested foods, and drugs.
Microbiological Tests: In these tests, the blood is examined for microorganisms, such as bacteria, viruses, and viral particles, fungi, and parasites, and for antibodies that form against them.
How They Are Done
The most convenient site for taking a blood sample is a vein at the bend in the elbow. A tourniquet is applied to the upper arm, and the blood is withdrawn through a needle into a syringe. The procedure causes only mild discomfort. Up to 20 ml of blood may be required, but, as the circulation contains 4 to 5 liters, loss of this small proportion has no harmful effect. If only a few drops are needed, they may be obtained by pricking a finger. Some tests require arterial blood, which is taken from the wrist or the groin. Obtaining such blood is a more difficult procedure that may cause some discomfort.
The sample may be allowed to clot, leaving its clear serum for examination, or an anticoagulant may be added to allow study of the cells and clotting factors. The sample is then sent to the laboratory, where one or more of the hundreds of available tests are performed. In some laboratories, modern computerized analyzers are used to perform many different tests simultaneously on one small sample of blood. The printed results compare each value with the accepted normal range of that test. Each laboratory produces its own normal ranges that depend on the method and the ingredients of the test, and sometimes on the age and sex of the patient.
Used in 3 Term definitions
Used in 3 Term definitions