The technique is able to detect one molecule of nucleic acid within 100,000 cells. PCR tests fall within the realm of rapid virus diagnostic tests being considerably more rapid than most virus culture techniques and equal in speed to most serological tests. Specificity False positive results due to contamination are the major pitfall of this test. Because of the enormous magnifying ability of the test, any contamination of the test system e.g. from the operator or from residual material in testing utensils or even by air contamination, can result in false positive reactions. As a result, meticulous attention to very stringent standards of cleanliness and laboratory isolation are required to set up the test system.
Reagents used in the test are still very expensive.
Thus, even strains with sufficiently different sequences from the primers will be missed. Virus culture, on the other hand, will diagnose any cultivable virus which is responsible for the infection. Quantitative PCR Standard PCR tests provide a qualitative result of the presence or absence of virus. PCR is also useful in cases where serology would not be helpful, for example, suspected HIV infection in an infant up to 18 months of age where maternal antibodies cannot be distinguished from those of the infant. Quantitative PCR is of great benefit in prognosis and therapeutic monitoring of patients on antiviral drug therapy.