The avidity of specific IgG antibodies against cytomegalovirus is used to distinguish between recent and past virus infections in transplanted patients and pregnant women, where IgM antibodies are not helpful in determining the infection.
Cytomegalovirus (CMV) belongs to the family of herpesviruses and is also known as human herpesvirus type 5 (HHV-5). It is a widespread virus and it is estimated that, depending on the area, 40 to 100% of the population may be infected. In most people, the virus remains latent and causes no symptoms. In rare cases, it can cause hepatitis or pneumonia in adult patients. In immunosuppressed patients, however, CMV infection can have devastating effects. In AIDS patients, CMV infection can cause pneumonitis, esophagitis, colitis, encephalitis, hepatitis, and retinitis leading to blindness. In transplanted patients, CMV infection is considered to be a very important complication that can often lead to death. CMV infection during pregnancy can cause mental retardation and microcephaly in the newborn. CMV is found in all secretions of the body.
The best evidence for the determination of active cytomegalovirus infection is the significant change in antibody titer in two specimens spaced apart (approximately 2 weeks), where both tests are performed in the same laboratory at the same time.
Determination of avidity is a diagnostic method used to differentiate recent (acute) from past cytomegalovirus infections in a patient's serum. Avidity (or affinity) is defined as the binding strength of the antibody (in serum sample) to the corresponding antigen. The low affinity of IgG antibodies in the early stage of infection may be differentiated from the high affinity of antibodies associated with past infection. Determination of the affinity of IgG antibodies is an additional analysis in classical serological tests in relation to the status of infection with cytomegalovirus.
The distinction between recent (acute) and past cytomegalovirus infections may be of major importance in the clinical management of transplanted and pregnant women. Although almost all people with recent CMV infections have positive IgM antibodies against cytomegalovirus, some patients with past infections may also develop specific IgM after the virus is reactivated. Therefore, the detection of specific IgM is not a reliable indicator of recent cytomegalovirus infection. Measurement of the affinity of specific IgG antibodies against cytomegalovirus may help distinguish recent from past infections. Although a low-avidity index is a reliable indicator of CMV infection over the past 6 months, a high-avidity index is more clinically relevant. A high avidity index essentially excludes the chance of infection in the past 4 months.
Avidity index values should be taken into account in the context of other laboratory findings and clinical symptoms.
Laboratory test results are the most important parameter for the diagnosis and monitoring of all pathological conditions. 70%-80% of diagnostic decisions are based on laboratory tests. The correct interpretation of laboratory results allows a doctor to distinguish "healthy" from "diseased".
Laboratory test results should not be interpreted from the numerical result of a single analysis. Test results should be interpreted in relation to each individual case and family history, clinical findings, and the results of other laboratory tests and information. Your personal physician should explain the importance of your test results.
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