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Hemoglobin Testing: Purpose & Types

Instructor: Julie Eiler
This lesson briefly describes the function of hemoglobin in the blood. Various types of commonly tested hemoglobin levels are defined as well as indications for abnormal levels.

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Blood is the vital fluid that carries essential elements to the different parts of the body - things like healing white blood cells, energy providing nutrients, and of course oxygen. These elements are whisked downstream in cells and molecules like ships on a river. One of the most important molecules, oxygen, is carried on red blood cell ''boats'' in special cargo containers called hemoglobin.

Hemoglobin is a protein found in erythrocytes, or red blood cells, circulating the body. Hemoglobin is the compound in blood that carries oxygen, therefore hemoglobin concentration is indicative of blood's oxygen-carrying capacity. Patients with inadequate or abnormal hemoglobin production may have symptoms of deoxygenation such as pale skin, fatigue, and lethargy.

Hemoglobin in Laboratory Medicine

Testing

Hemoglobin levels are tested to determine abnormal conditions like anemia, a broad term to describe low or abnormal levels of red blood cells or hemoglobin. Most hemoglobin tests are done through venous blood samples, except for fetal hemoglobin, which is done by performing a heel stick. Blood is taken from the patient using a needle and put into a standard 7mL blood tube with an anticoagulant additive. The tube should be gently inverted (to mix the additive), but not agitated.

Factors that can affect accuracy of the test are delayed testing without sample refrigeration and certain medications a patient may be taking that decrease levels, such as antibiotics, sulfonamides, aspirin, and antineoplastics (drugs to prevent cancer growth).

To measure the various types of hemoglobin in a blood sample, electrophoresis is done. This test uses an electrical current to separate the hemoglobin types.

Hemoglobin Types and Indications

There are various types of hemoglobin that may be tested to identify possible complications. The normal hemoglobin is referred to as Hemoglobin A1, or HbA1, and makes up 90% of the hemoglobin in blood. Low levels of normal hemoglobin may indicate blood loss or anemia. There are actually a few hundred abnormal types of hemoglobin; some commonly tested types are discussed below.

Hemoglobin A2, or HbA2, is normal hemoglobin present in low levels in normal adults. When this type of hemoglobin is seen in high levels, it is usually a sign of a type of anemia called thalassemia. In thalassemia, normal hemoglobin levels are low, causing HbA2 levels to be disproportionately higher. Thalassemia is a genetic disorder where not enough hemoglobin is produced. Thalassemia is rare in the United States, but common in the Mediterranean and Southeast Asia.

Fetal hemoglobin, or HbF, is a type of hemoglobin produced in utero. It gradually decreases at birth and is usually depleted within the first month as adult hemoglobin is produced. Persistent levels of HbF after infancy could indicate a thalassemia. As mentioned, testing of fetal hemoglobin in neonates is performed on capillary blood through a heel stick. The concentrations are higher than normal values, and depend on the amount of blood received from the umbilical cord.

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