Comparison of the classical immunofluorescent antibody tests for Epstein-Barr virus with commercially available test kits

Clinical performance of a prefabricated immunofluorescence assay for nasopharyngeal cancer screening

BACKGROUND

Epstein-Barr virus (EBV) IgA serology for viral capsid antigen (VCA) and early antigen (EA) aids early detection of nasopharyngeal cancer (NPC), resulting in improved survival. We evaluated the diagnostic performance of a prefabricated immunofluorescent assay (IFA) for NPC screening in high-risk individuals.

METHODS

Sera from 96 biopsy-proven patients with NPC diagnosed at the outpatient clinic and 96 healthy family members were tested for EBV-VCA IgA and EBV-EA IgA using the prefabricated IFA from EUROIMMUN (EI) and the traditional immunofluorescence method.

RESULTS

The AUC of EI EBV-VCA IgA and EBV-EA IgA was 0.907 (95% confidence interval [CI]: 0.894-0.965) and 0.898 (95% CI: 0.848-0.947), respectively. Combined testing with the prefabricated assay at a threshold of VCA ≥1:320 or EA ≥1:10 showed 92.7% sensitivity and 81.2% specificity. Overall, the traditional EBV-EA IgA assay demonstrated the best accuracy (sensitivity 91.7% and specificity 96.9%) at a threshold of ≥1:5.

CONCLUSION

While the traditional IFA method was more accurate, the prefabricated IFA test kit can be a useful tool for NPC screening in high-risk populations.

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 Programs (QAP) on serologic assays for infectious Mononucleosis (IM) have identified a number of important problems in laboratory diagnosis of this condition. A wide range of assays for the diagnosis of acute Epstein-Barr virus (EBV) infection are available, although heterophile antibody tests are still the most frequently performed procedures for the 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 screening, due to their inferior sensitivity of less than 50% in children and 80-90% in adults and specificity of 95% compared to EBV-specific assays. For these reasons the use of heterophile tests is discouraged. Although EBV-specific serology has traditionally been done by immunofluorescence (IF), the use of reliable ELISA methods using purified EBV-antigens is increasing. False negative EBV VCA IgM ELISA test results were obtained by laboratories using unpurified or unspecified VCA antigens. As only five laboratories used these tests in the 1992 QAP, the tests' true performances could not be properly assessed, suggesting the need for independent studies. Variable results were obtained by laboratories using commercial EBNA IgG assays (in addition to EBV IgM) suggesting that an assessment of these kits would also be worthwhile. The QAP 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 the 1992 and 1993 QAP, laboratory performance of both heterophile and EBV-specific tests was better with non-reactive serum specimens (99% (correct) than with reactive serum specimens (90% correct).