Blood test

A blood test is a lab analysis of a blood sample, typically taken from a vein in the arm with a hypodermic needle or from a fingerprick. Several tests for specific blood components—like glucose or cholesterol—are often combined into a single panel, known as a blood panel or blood work.

In healthcare, these tests help assess physiological and biochemical conditions, such as disease, mineral levels, how well a drug is working, and organ function. Common clinical panels include a basic metabolic panel and a complete blood count. Blood tests are also used in drug testing to detect substance abuse.

Extraction

Blood is usually drawn from a vein because it is a minimally invasive way to collect cells and plasma for analysis. Since blood flows throughout the body, delivering oxygen and nutrients and carrying away waste, its condition both influences and reflects many medical issues. This makes blood tests the most common medical tests performed. When only a few drops are needed, a fingerstick is used instead.

Blood can also be taken from indwelling arterial, central venous, or peripheral venous lines. Phlebotomists, lab practitioners, and nurses typically draw blood in clinics, offices, or through home visits; in emergencies, paramedics and physicians may do it. Respiratory therapists are trained to draw arterial blood for arterial blood gas analysis.

Biochemical analysis

A basic metabolic panel measures sodium, potassium, chloride, bicarbonate, blood urea nitrogen (BUN), magnesium, creatinine, glucose, and sometimes calcium. Cholesterol-focused tests determine LDL and HDL cholesterol and triglyceride levels. Some tests, like glucose or lipid profiles, require fasting for eight to twelve hours beforehand.

Most blood is taken from a vein, but specialized tests like arterial blood gas require blood from an artery. Arterial blood gas analysis mainly monitors carbon dioxide and oxygen levels for lung function, and also measures pH and bicarbonate for certain metabolic conditions. A regular glucose test is a single measurement, while a glucose tolerance test involves repeated sampling to see how quickly the body processes glucose.

For a complete blood count (CBC), samples should ideally be analyzed soon after collection to avoid pre-analytical changes. If delays are unavoidable, EDTA-anticoagulated blood can be refrigerated at 2–8 °C, though stability varies by parameter.

Hemoglobin, red blood cell count, and white blood cell count are generally more stable under refrigeration than platelet-related measures and some red blood cell indices. Labs should follow validated storage guidelines and consider potential changes when interpreting delayed samples. Blood tests are also used to identify autoimmune diseases and Immunoglobulin E-mediated food allergies (see also Radioallergosorbent test).

Blood test results must be interpreted using the reference ranges provided by the lab that performed the test. Example ranges are commonly shown. After analysis, patients may receive a report with abbreviations, such as those listed below. Common test types include protein electrophoresis, Western blot, liver function tests, polymerase chain reaction (DNA), Northern blot (RNA), and tests for sexually transmitted diseases.

DNA profiling is now possible with very small blood samples and is used in forensic science and diagnosis. Cellular evaluations include full blood count, hematocrit, mean corpuscular volume (MCV), mean corpuscular hemoglobin concentration (MCHC), erythrocyte sedimentation rate (ESR), and cross-matching for blood type before transfusions. Blood cultures are taken if infection is suspected; positive results and sensitivity data help guide treatment.

Saliva tests

Future alternatives to blood tests include saliva tests, which were reported in 2008 as a potentially cheaper option, since saliva contains 20% of the proteins found in blood. However, saliva testing may not work for all markers—lipid levels, for example, cannot be measured this way.

Microemulsion

In February 2011, Canadian researchers at the University of Calgary announced a microchip for blood tests, called a microemulsion, which captures a blood droplet inside another substance to control droplet size and spacing. This could improve efficiency, accuracy, and speed while lowering costs. In March 2011, a team from UC Berkeley, DCU, and the University of Valparaíso developed SIMBAS, another microchip-based approach.