The affinity of specific IgG antibodies against cytomegalovirus is used to distinguish between recent and older virus infections in transplanted patients and pregnant women, where IgM antibodies are not auxiliary to determining of infection.
Cytomegalovirus or megacytovirus (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 retinal 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 an active cytomegalovirus infection is the significant change in antibody titre 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 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 different from the high affinity of antibodies associated with earlier infection. Determination of the affinity of IgG antibodies is an additional analysis in classical serological control in relation to the status of infection with cytomegalovirus.
The distinction between recent (acute) and older cytomegalovirus infections may be of major importance in the clinical management of transplanted and pregnant women. Although almost all people with recent CMV infection have positive IgM antibodies against cytomegalovirus, some patients with older infections may also develop specific IgM after the virus is reactivated. Therefore, the detection of specific IgM is not a reliable indicator of a recent cytomegalovirus infection. Measurement of the affinity of specific IgG antibodies against cytomegalovirus may help distinguish recent from older infections. Although a low affinity index is a reliable indicator of CMV infection over the past 6 months, a high affinity index is more clinically relevant. A high viability index essentially excludes the chance of infection in the past 4 months.
Affinity 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. 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.
At Diagnostiki Athinon we answer any questions you may have about the test you perform in our laboratory and we contact your doctor to get the best possible medical care.