CONFIRMING DIAGNOSIS Signs and symptoms may occur at any time after infection with HIV, but AIDS isn’t officially diagnosed until the patient’s CD4+ T-cell count falls below 200 cells/µl.
The most commonly performed tests, antibody tests, indicate HIV infection indirectly by revealing HIV antibodies. The recommended protocol requires initial screening of individuals and blood products with an enzyme-linked immunosorbent assay (ELISA). A positive ELISA should be repeated and then confirmed by an alternate method, usually the Western blot or an immunofluorescence assay. The radioimmunoprecipitation assay is considered more sensitive and specific than the Western blot, but because it requires radioactive materials, it’s a poor choice for routine screening. In addition, antibody testing isn’t reliable. Because people produce detectable levels of antibodies at different rates — a “window” varying from a few weeks to as long as 35 months in one documented case — an HIV-infected person can test negative for HIV antibodies. Antibody tests are also unreliable in neonates because transferred maternal antibodies persist for 6 to 10 months. To overcome these problems, direct tests are used, including antigen tests (p24 antigen), HIV cultures, nucleic acid probes of peripheral blood lymphocytes, and the polymerase chain reaction. (See Laboratory tests for diagnosing and tracking HIV and assessing immune status, page 396.)
Additional tests to support the diagnosis and help evaluate the severity of immunosuppression include CD4+ and CD8+ T-lymphocyte subset counts, erythrocyte sedimentation rate, complete blood cell count, serum beta2-microglobulin, p24 antigen, neopterin levels, and anergy testing. Because many opportunistic infections in AIDS patients are reactivations of previous infections, patients are also tested for associated neoplasms, infections, and STDs.
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Source: Professional Guide to Diseases (Eighth Edition), 2005
Severe combined immunodeficiency disease:
Diagnosis
(Handbook of Diseases)
Clinical indications point to the diagnosis. Most infants with SCID suffer recurrent overwhelming infections within 1 year of birth. Some are diagnosed after a severe reaction to vaccination.
Defective humoral immunity is difficult to detect before an infant is 5 months old. Before age 5 months, even normal infants have very small amounts of the serum immunoglobulins (Ig) IgM and IgA, and normal IgG levels merely reflect maternal IgG. However, severely diminished or absent T-cell number and function and lymph node biopsy showing absence of lymphocytes can confirm the diagnosis of SCID.
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Source: Handbook of Diseases, 2003
Common variable immunodeficiency:
Diagnosis
(Handbook of Diseases)
Characteristic diagnostic markers in this disorder include decreased serum immunoglobulin (Ig) M, IgA, and IgG detected by immunoelectrophoresis, along with a normal circulating B-cell count. Antigenic stimulation confirms an inability to produce specific antibodies; cell-mediated immunity may be intact or delayed. X-rays usually show signs of chronic lung disease or sinusitis.
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Source: Handbook of Diseases, 2003
Human immunodeficiency virus infection:
Diagnosis
(Handbook of Diseases)
The CDC defines AIDS as an illness characterized by one or more “indicator” diseases coexisting with laboratory evidence of HIV infection and other possible causes of immunosuppression. The CDC’s current AIDS surveillance case definition requires laboratory confirmation of HIV infection in people who have a CD4+ T-cell count of 200 cells/µl or who have an associated clinical condition or disease.
Antibody tests
The most commonly performed tests, antibody tests indicate HIV infection indirectly by revealing HIV antibodies. The recommended protocol requires initial screening of individuals and blood products with an enzyme-linked immunosorbent assay (ELISA). A positive ELISA should be repeated and then confirmed by an alternate method, usually the Western blot or an immunofluorescence assay. However, antibody testing isn’t always reliable. Because the body takes a variable amount of time to produce a detectable level of antibodies, a “window” varying from a few weeks to as long as 35 months in one documented case allows an HIV-infected person to test negative for HIV antibodies.
Antibody tests are also unreliable in neonates because transferred maternal antibodies persist for 6 to 10 months. To overcome these problems, direct testing is performed to detect HIV. Direct tests include antigen tests (p24 antigen), HIV cultures, nucleic acid probes of peripheral blood lymphocytes with determination of HIV-1 ribonucleic acid levels, and the polymerase chain reaction.
Other tests
Additional tests to support the diagnosis and help evaluate the severity of immunosuppression include CD4+ and CD8+ T-lymphocyte subset counts, erythrocyte sedimentation rate, complete blood count, serum beta2-microglobulin, p24 antigen, neopterin levels, and anergy testing. Because many opportunistic infections in patients are reactivations of previous infections, patients are also tested for syphilis, hepatitis B, tuberculosis, toxoplasmosis and, in some areas, histoplasmosis.
» READ BOOK EXCERPT ONLINE »
Source: Handbook of Diseases, 2003
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