DIFFICULTIES WITH THE SEROLOGIC DIAGNOSIS OF INFECTIOUS-MONONUCLEOSIS- A REVIEW OF THE RCPA QUALITY ASSURANCE PROGRAMS

The Royal College of Pathologists of Australasia's Quality Assurance P rograms (QAP) on serologic assays for Infectious Mononucleosis (IM) ha ve identified a number of important problems in laboratory diagnosis o f this condition. A wide range of assays for the diagnosis of acute Ep stein-Ban virus (EBV) infection are available, although heterophile an tibody tests are still the most frequently performed procedures for th e diagnosis of IM. In 1993, eighty-six (54%) of the 159 participating laboratories performed only a heterophile test; of these, 71% did not provide an interpretation of their results and none mentioned the need for confirmatory EBV-specific antibody testing. This revealed a lack of appreciation that heterophile tests should only be used for screeni ng, due to their inferior sensitivity of less than 50% in children and 80-90% in adults and specificity of 95% compared to EBV-specific assa ys. For these reasons the use of heterophile tests is discouraged. Alt hough EBV-specific serology has traditionally been done by immunofluor escence (IF), the use of reliable ELISA methods using purified EBV-ant igens is increasing. False negative EBV VCA IgM ELISA test results wer e obtained by laboratories using unpurified or unspecified VCA antigen s. As only five laboratories used these tests in the 1992 QAP, the tes ts' true performances could not be properly assessed, suggesting the n eed for independent studies. Variable results were obtained by laborat ories using commercial EBNA IgG assays (in addition to EBV IgM) sugges ting that an assessment of these kits would also be worthwhile. The QA P reaffirm that reliable EBV IgM detection is the most useful test for the diagnosis of IM, even where other EBV markers are also used. In t he 1992 and 1993 QAP, laboratory performance of both heterophile and E BV-specific tests was better with non-reactive serum specimens (99% co rrect) than with reactive serum specimens (90% correct).