Tests commonly used for diagnosis of HIV infection are:
- HIV antibody test (ELISA)
- HIV viral culture
- HIV immune complex dissociated (ICD) p24 antigen test
- HIV DNA PCR
In children the 2 commonly used tests are HIV ELISA and HIV DNA PCR.
Diagnosis of HIV in children less than 18 months of age
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HIV ICD p24 antigen has low sensitivity for diagnosis of HIV infection in infants. In children less than 18 months of age, HIV ELISA is not reliable due to presence of maternally transmitted HIV antibodies which may lead to an erroneously positive report. Hence in infants, HIV DNA PCR is the gold standard. In India, PCR techniques still have to be standardized. Though sensitivity of these PCR tests is very high, the specificity ranges from 50% to 60%. Thus chance of a false positive test with PCR is very high. Contamination of PCR technique is the commonest problem for these erroneous results. HIV viral culture can also be used of diagnosis of HIV infection in infants but it is time consuming and costly and not readily available.
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Diagnosis of HIV in Children above 18 Months of Age
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With the advent of 4th generation ELISA kits (Rapid ELISA), the sensitivity and specificity of HIV ELISA is 100% and 99% respectively and chances of false positive and false negative ELISA test are negligible. ELISA test can be used for detection of HIV infection in children above 18 months of age.
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Confirmation of HIV infection:
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For diagnosis of HIV infection, confirmation of a positive result should be done by a repeat test. At least 2 tests should be positive for identifying HIV infection. Confirmation of a positive ELISA test in a child more than 18 months of age by a Western Blot Test is ideal. It detects antibodies against specific HIV antigens and is done by plasma electrophoresis, thus eliminating the false positive ELISA test. However, Western Blot Test is quite expensive and in a clinically suspected case in a resource limited setting, confirmation of positive HIV status by 2 or 3 ELISA tests using different kits on the same sample (one of which is a Rapid ELISA), the infection can be confirmed.
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