A venipuncture performed using a vacutainer

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. They are also used in drug tests.

  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.^[1]

If only a few drops of blood are needed, a fingerstick is performed instead of drawing blood from a vein.^[2]

Phlebotomists, laboratory practitioners 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 gases.^[3][4]

  Types of blood tests

  Samples of human blood collected for testing. The barcodes contain information that is used to identify the individual from whom the sample was taken and the blood test requested.

  Biochemical analysis

A basic metabolic panel measures sodium, potassium, chloride, bicarbonate, blood urea nitrogen (BUN), magnesium, creatinine, glucose, and sometimes includes calcium. Blood tests focusing on cholesterol levels can determine LDL and HDL cholesterol levels, as well as triglyceride levels.^[5]

Some blood tests, such as those that measure glucose, cholesterol, or for determining the existence or lack of STD, require fasting (or no food consumption) eight to twelve hours prior to the drawing of the blood sample.^[6]

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.^[7]

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.^[8]

  Normal ranges

  Molecular profiles

• Protein electrophoresis (general technique—not a specific test)
• Western blot (general technique—not a specific test)
• Liver function tests
• Polymerase chain reaction (DNA). DNA profiling 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)
• Sexually transmitted diseases

  Cellular evaluation

• 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.

  Future alternatives

  Saliva tests

In 2008, scientists announced that the more cost effective saliva testing could eventually replace some blood tests, as saliva contains 20% of the proteins found in blood.^[11]

  Microemulsion

February 2011: Canadian researchers have developed a microchip for blood tests. It is called microemulsion, a droplet of blood captured inside a layer of another substance. It can control the exact size and spacing of the droplets. The new test could improve the efficiency, accuracy and speed of laboratory tests while also doing it cheaply. The microchip costs $25, whereas the robotic dispensers currently in use cost around $10,000. ^[12]

  SIMBAS

March 2011: A team of researchers from UC Berkeley, DCU and University of Valparaíso have developed lab-on-a-chip that can diagnose diseases within 10 minutes without the use of external tubing and extra components. It is called Self-powered Integrated Microfluidic Blood Analysis System (SIMBAS). It uses tiny trenches to separate blood cells from plasma (99 percent of blood cells were captured during experiments). Researchers used plastic components, to reduce manufacturing costs.^[13][14]

  See also

• Biomarker (medicine), a protein or other biomolecule measured in a blood test
• Blood film, a way to look at blood cells under a microscope
• Hematology, the study of blood
• Lipid profile, estimation of lipid types in blood
• Reference ranges for blood tests (with a much longer list)
• Schumm test, a common test for blood mismatch
• Urinalysis, another common style of body fluid test

  References