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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:

Overview

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

Does employing general practitioners to provide care for patients with non‐urgent problems in emergency departments decrease resource use and costs?

An important portion of patients who attend hospital emergency departments (EDs) present with health problems that are classified as non‐urgent. With many EDs experiencing long‐waits and overcrowding, it has been suggested that providing primary care services in EDs for patients with non‐urgent problems may be an efficient and cost‐effective alternative to emergency care.

Screening for colorectal cancer using the faecal occult blood test, Hemoccult

Regular screening of faeces for blood can detect colorectal cancer earlier and hence may reduce mortality in populations at risk, such as older patients. The screening test used in these trials to detect colorectal (bowel) cancer was the faecal occult blood test (FOBT). If the FOBT is positive, the bowels are examined closely with further diagnostic test (coloscopy, flexible sigmoidoscopy, double‐contrast barium enema), but these tests often cause discomfort and can cause serious adverse consequences. As blood identified in faeces may be due to several reason (unrelated to cancer), it may cause people unnecessary stress and expose them to possible harm. This review found that FOBT screening is likely to avoid approximately 1 in 6 colorectal cancer deaths.

Use of thromboelastography (TEG) or thromboelastometry (ROTEM) analysers versus usual care to monitor transfusion of blood products in surgical patients

There is a lack of knowledge from previous research to support the use of TEG or ROTEM to guide the transfusion strategy in patients with massive bleeding. Massive transfusion is defined as the total replacement of a patient's blood volume in a period of 24 hours, a transfusion of at least four red blood cell concentrates within one hour, or the replacement of 50% of the total blood volume within three hours. In the present systematic review we set out to assess the benefits and harms of TEG or ROTEM in patients at risk of major transfusion requirement. We identified nine randomized trials comparing TEG or ROTEM (776 participants) to transfusion guided by clinical judgement and standard laboratory tests, or both, in the adult cardiac surgery and liver transplantation settings. Additionally, we found two ongoing trials but we were unable to retrieve any data from them. We could not identify any beneficial effect of TEG or ROTEM on patient survival. However, we did identify positive results in our predefined outcomes such as reduced bleeding and reduced proportion of patients requiring transfusion of both platelets and fresh frozen plasma. We could not identify any harms or adverse events in patients caused by the application of TEG or ROTEM.

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Summaries for consumers

Does employing general practitioners to provide care for patients with non‐urgent problems in emergency departments decrease resource use and costs?

An important portion of patients who attend hospital emergency departments (EDs) present with health problems that are classified as non‐urgent. With many EDs experiencing long‐waits and overcrowding, it has been suggested that providing primary care services in EDs for patients with non‐urgent problems may be an efficient and cost‐effective alternative to emergency care.

Screening for colorectal cancer using the faecal occult blood test, Hemoccult

Regular screening of faeces for blood can detect colorectal cancer earlier and hence may reduce mortality in populations at risk, such as older patients. The screening test used in these trials to detect colorectal (bowel) cancer was the faecal occult blood test (FOBT). If the FOBT is positive, the bowels are examined closely with further diagnostic test (coloscopy, flexible sigmoidoscopy, double‐contrast barium enema), but these tests often cause discomfort and can cause serious adverse consequences. As blood identified in faeces may be due to several reason (unrelated to cancer), it may cause people unnecessary stress and expose them to possible harm. This review found that FOBT screening is likely to avoid approximately 1 in 6 colorectal cancer deaths.

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).

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Terms to know

Blood
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.
Enzymes
Protein made by the body that brings about a chemical reaction - for example, the enzymes produced by the gut to aid digestion.
Hematocrit
A measure that tells what portion of a blood sample consists of red blood cells. Low hematocrit suggests anemia or massive blood loss.
Hemoglobin
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.
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.
Red Blood Cells (Erythrocytes)
A cell that carries oxygen to all parts of the body.
Triglycerides
One of the major forms of fat that is produced in the liver and found in the blood.
White Blood Cells (Leukocytes)
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.

More about Blood Tests

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

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