HIV and Your Complete Blood Count (CBC)

If you have HIV, your doctor will routinely perform blood tests to evaluate the status of your immune system (as measured by the CD4 count) and the level of viral activity in your body (as measured by the HIV viral load).

In addition to these tests, others will be performed to monitor for side effects or medical issues arising from the infection itself. Central to this is a panel of tests called the complete blood count (CBC). The test measures the composition of cells in a sample of blood to flag for changes that fall outside of the "normal" range of values.

By doing so, a CBC can reveal if an infection is developing or if an antiretroviral drug like AZT (zidovudine) is causing anemia.

A CBC measures constituent cells in your blood, including white blood cells (leukocytes), red blood cells (erythrocytes), and platelets (thrombocytes). The test is typically ordered every three to six months but may be ordered more frequently if there is an active infection or illness.

White Blood Cell Count

White blood cells are a subset of cells produced in bone marrow whose primary role is to fight infection. A white blood cell count (WBC) is one of the panel of tests included in the CBC that measures not only the total number of leukocytes but also the different types of white blood cells in a blood sample, namely:

• Basophils
• Eosinophils
• Lymphocytes
• Monocytes
• Neutrophils

Within the context of HIV, an elevated WBC typically means that your body is fighting an infection. Other tests can then be performed to pinpoint the cause.

An elevation of certain white blood cells may indicate a specific type of infection or an allergic inflammatory response. For example, higher than normal eosinophils may suggest a parasitic infection like toxoplasmosis, while elevated basophils can develop in people with a hypersensitive drug reaction.

By contrast, a low WBC suggests that some condition, either HIV- or non-HIV-related, is affecting the bone marrow's ability to produce white blood cells. When this occurs, the body is less able to fight infection.

A decrease in white blood cells may be the result of HIV medications (like AZT or ganciclovir), a minor viral infection, or a major opportunistic infection like tuberculosis.

Red Blood Cell Count

Red blood cells are responsible for transporting oxygen from the lungs to cells and tissues of the body. A red blood cell count (RBC) is performed as part of the CBC to measure the total number of erythrocytes in a sample of blood along with other key values, such as:

• Hematocrit: The percentage of blood volume taken up by red blood cells
• Hemoglobin: The amount of protein in red blood cells responsible for carrying oxygen molecules

A low RBC is often indicative of anemia, a condition in which you lack enough healthy red blood cells to carry adequate oxygen to your body's tissues.

Within the context of HIV, anemia is known to be a common side effect of AZT. Anemia can also be due to an active infection or other causes, both HIV- and non-HIV-related.

By contrast, an abnormally high RBC, referred to as polycythemia, is less commonly associated with HIV infection. What that said, people with HIV on testosterone replacement therapy (sometimes used to treat HIV wasting or HIV-associated hypogonadism) will often experience a higher-than-normal RBC.

Platelet Count

Platelets are colorless blood cells involved in blood clotting. Platelet counts are rarely so high as to cause health problems.

By contrast, low platelet counts (thrombocytopenia) can lead to easy bleeding or bruising. Severe cases can even result in potentially life-threatening internal bleeding.

Thrombocytopenia is associated with chronic HIV infection, primarily in people with advanced disease who are not yet on treatment. With that said, in anywhere from 5% to 15% of cases, thrombocytopenia is the first sign of the disease.

The initiation of antiretroviral therapy can generally resolve the condition by suppressing the inflammatory agents that contribute to low platelet counts.

Certain HIV drugs like Fuzeon (enfuvirtide) can also cause low platelet counts, as well as opportunistic infections like cytomegalovirus (CMV) and mycobacterium avium complex (MAC).

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