blood test

blood test

blood test, examination of blood routinely or as an aid in diagnosing a suspected disease. Tests may be performed on whole blood or on the plasma portion only. Blood typing identifies the proteins at specific sites on red blood cells, a necessity in determining compatibility for blood transfusion. Human Lymphocyte Antigens (HLA) is a form of white blood cell typing prerequisite for organ and bone marrow transplants. The Coulter Cell Counter is widely used in electronic counts of red blood cells for the diagnosis of anemia and polycythemia. White cell counts are vital in detecting infections or in confirming leukemia. Serum or plasma may be collected, cultured, and inoculated with bacteria or other substances for the purpose of detecting the body's reaction to infections, cancer, or HIV, the virus that causes AIDS. Plasma may also be examined for evidence of functional disorders, e.g., for blood sugar in testing for diabetes mellitus. Blood tests for tumor markers, such as prostate-specific antigen, are effective in detecting cancer in high risk groups. Almost all blood tests are now performed by electronic equipment, and results are evaluated and printed out by computer.

Laboratory examination of the physical and chemical properties and components of a sample of blood. Analysis includes number of red and white blood cells (erythrocytes and leukocytes); red cell volume, sedimentation (settling) rate, and hemoglobin concentration; blood typing; cell shape and structure; hemoglobin and other protein structure; enzyme activity; and chemistry. Special tests detect substances characteristic of specific infections.

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A blood test is a laboratory analysis performed on a blood sample that is usually extracted from a vein in the arm using a needle, or via fingerprick.

Blood tests are used to determine physiological and biochemical states such as disease, mineral content, drug effectiveness, and organ function. Although the term blood test is used, most routine tests (except for most haematology) are done on plasma or serum instead of blood cells.

Extraction

Venipuncture is useful as it is a relatively non-invasive way to obtain cells, and extracellular fluid (plasma), from the body for analysis. Since blood flows throughout the body, acting as a medium for providing oxygen and 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. Phlebotomists, laboratory technicians and nurses are those charged with patient blood extraction. However, in special circumstances, and emergency situations, paramedics and physicians sometimes extract blood. Also, respiratory therapists are trained to extract arterial blood for arterial blood gasses.

Types of blood tests

Biochemical analysis

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

Some blood tests, such as measuring glucose, cholesterol, or for STD screening require fasting (or no food consumption) eight to twelve hours prior to the blood test.

For the majority of blood tests, blood is usually obtained from the patient's vein. However, other specialized blood tests, such as the Arterial blood gas, require blood extracted from an artery. Blood gas analysis of arterial blood is primarily used to monitor carbon dioxide and oxygen levels related to pulmonary function. But, it is also used to measure blood pH and bicarbonate levels for certain metabolic conditions.

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.

Normal ranges

Test Low High Unit Comments
Sodium (Na) 136 145 mmol/L
Potassium (K) 3.5 4.5 mmol/L
Urea 2.5 6.4 mmol/L BUN - blood urea nitrogen
Urea 7 18 mg/dL
Creatinine - male 62 115 μmol/L
Creatinine - female 53 97 μmol/L
Creatinine - male 0.7 1.3 mg/dL
Creatinine - female 0.6 1.1 mg/dL
Glucose (fasting) 3.9 5.8 mmol/L See also glycosylated hemoglobin
Glucose (fasting) 70 105 mg/dL

Molecular profiles

Cellular evaluation

Future alternatives

In 2008, scientists announced that the more cost effective saliva tests could eventually replace some blood tests, as saliva contains 20% of the proteins found in blood.

See also

References

External links

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