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Blood Tests

Blood tests help doctors check for certain diseases and conditions. They also help check the function of your organs and show how well treatments are working.

PubMed Health Glossary
(Source: NIH - National Heart, Lung, and Blood Institute)

Blood Tests

Blood tests help doctors check for certain diseases and conditions. They also help check the function of your organs and show how well treatments are working.

Specifically, blood tests can help doctors:

  • Evaluate how well organs - such as the kidneys, liver, thyroid, and heart - are working
  • Diagnose diseases and conditions such as cancer, HIV/AIDS, diabetes, anemia (uh-NEE-me-eh), and coronary heart disease
  • Find out whether you have risk factors for heart disease
  • Check whether medicines you're taking are working
  • Assess how well your blood is clotting


Blood tests are very common. When you have routine checkups, your doctor may recommend blood tests to see how your body is working.

Many blood tests don't require any special preparations. For some, you may need to fast (not eat any food) for 8 to 12 hours before the test. Your doctor will let you know how to prepare for blood tests.

During a... Read more about Blood Tests

What works? Research summarized

Evidence reviews

Immunochemical versus guaiac fecal occult blood tests

Bibliographic details: Piper M A.  Immunochemical versus guaiac fecal occult blood tests. Chicago, IL, USA: Blue Cross and Blue Shield Association, Technology Evaluation Center. TEC Assessment Program; 19(5). 2004

Diagnostic accuracy and cost-effectiveness of faecal occult blood tests (FOBT) used in screening for colorectal cancer: a systematic review

This review found that direct comparisons indicated better performance from immunochemical faecal occult blood tests, compared with guaiac faecal occult blood tests, but the evidence was low quality. Indirect comparisons found no difference. Poor reporting of the evidence limited the scope of the review.

Diagnostic value of laboratory tests in identifying serious infections in febrile children: systematic review

This review concluded that measuring inflammatory markers can be useful for diagnosing serious infections in febrile children in ambulatory settings. Measuring white blood cell count was less useful for ruling in serious infection and not useful for ruling out serious infection. This tentative conclusion is likely to be reliable, although possibility of publication bias should be borne in mind.

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Summaries for consumers

Thyroid function tests

The thyroid is a vitally important hormonal gland, which mainly works for the body’s metabolism. It is located in the front part of the neck below the voice box and is butterfly-shaped. The functions of the thyroid gland include the production of the thyroid hormones triiodothyronine (T3) and tetraiodothyronine, also called thyroxine (T4).

Bowel cancer: Testing for occult blood in the stool

Stool tests can find traces of blood that may be caused by tumors or polyps. A positive test should be followed up by a colonoscopy to find out whether a tumor or an early stage of a tumor really is the cause. It has been proven that the stool test can then lower the risk of dying of bowel cancer.Bowel cancer and advanced bowel polyps can cause bleeding in the bowel. Stool tests – also called stool blood test, or fecal occult blood tests (FOBT) – can detect these traces of blood. But they do not provide a definite answer because only few tumors and polyps leave traces of blood in the stool. There are also harmless causes of blood in the stool, so stool tests are more of a preliminary test. If the results are abnormal, you will be referred to have a colonoscopy to find out the cause. Both the stool test and the following colonoscopy are covered by statutory health insurance in Germany for people aged 50 and above.Stool tests only provide an opportunity to find polyps or bowel cancer early if a bowel endoscopy is performed after abnormal findings in the stool test. So it only makes sense to do a stool test if you are also prepared to have an endoscopy of the bowel if necessary.Chemical stool tests are the most commonly used. These tests use a chemical reaction to detect traces of hemoglobin, a protein in red blood cells. They are the only stool tests covered by statutory health insurance in Germany. That is why we will look at how these tests work in more detail. Three chemical stool tests are used for screening tests covered by statutory health insurance in Germany: Hämoccult, HemoFec and HemoCare.

Understanding tests used to detect bone problems

Just like other tissues and organs in our body, bones can be affected by medical conditions too. These include things like fractures, signs of wear and tear, inflammations and cancer. Injuries and fractures are common in younger people. As we grow older, diseases like osteoporosis and osteoarthritis are more likely to develop. Various tests and examinations can be used to find out what is causing problems like pain or difficulties moving.

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Terms to know

A tissue with red blood cells, white blood cells, platelets, and other substances suspended in fluid called plasma. Blood takes oxygen and nutrients to the tissues, and carries away wastes.
Blood Plasma
The clear, yellowish, fluid part of the blood that carries the blood cells. The proteins that form blood clots are in plasma.
Bone Marrow
The soft, sponge-like tissue in the center of most bones. It produces white blood cells, red blood cells, and platelets.
Protein made by the body that brings about a chemical reaction - for example, the enzymes produced by the gut to aid digestion.
Erythrocytes (Red Blood Cells)
A cell that carries oxygen to all parts of the body.
A measure that tells what portion of a blood sample consists of red blood cells. Low hematocrit suggests anemia or massive blood loss.
A protein inside red blood cells that carries oxygen from the lungs to tissues and organs in the body and carries carbon dioxide back to the lungs.
Leukocytes (White Blood Cells)
A type of immune cell. Most white blood cells are made in the bone marrow and are found in the blood and lymph tissue. White blood cells help the body fight infections and other diseases. Granulocytes, monocytes, and lymphocytes are white blood cells.
Platelets (Thrombocytes)
A tiny piece of cell that is made by breaking off of a large cell in the bone marrow. Platelets are found in the blood and spleen. They help form blood clots to slow or stop bleeding, and to help wounds heal. Also called thrombocyte.
One of the major forms of fat that is produced in the liver and found in the blood.

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Other terms to know: See all 10
Blood, Blood Plasma, Bone Marrow

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