# Resolving Heterophile Antibody Interference in Viral Serology Using Blocking Tubes

## TL;DR

This study shows that using blocking tubes can reduce false-positive results in viral antibody tests caused by heterophile antibodies, improving the accuracy of clinical diagnoses.

## Contribution

The study demonstrates the effectiveness of heterophile blocking tubes in resolving interference in routine viral IgM serology tests.

## Key findings

- Heterophile blocking tubes significantly reduced reactivity levels and positivity rates for EBV and HSV IgM tests.
- Pretreatment with blocking tubes reclassified many patients with apparent primary EBV infection.
- The study highlights the high prevalence of heterophile antibody interference in common viral serology tests.

## Abstract

Despite their clinical utility, immunoassays are susceptible to various types of interference. In this study, we aimed to assess the extent of interference from heterophile antibodies in routine clinical tests and evaluate the effectiveness of heterophile blocking tubes (HBT) in mitigating such interference. We collected 185 residual serum samples that tested positive or equivocal in at least one IgM assay for Epstein–Barr virus (EBV), viral capsid antigen (VCA), herpes simplex virus (HSV), varicella‐zoster virus, cytomegalovirus (CMV), rubella virus, or Toxoplasma gondii. These samples were obtained from the clinical laboratory of a tertiary teaching hospital in Korea and tested between May and July 2024. For each sample, complete IgM and IgG results for all six pathogens were obtained by performing any missing assays. Each sample was then pretreated with HBT and reanalyzed, and the assay results were compared with those of untreated samples. HBT pretreatment significantly reduced both reactivity levels (e.g., EBV VCA: 32.2 ± 35.8 U/mL to 12.8 ± 15.6 U/mL; HSV: 1.4 ± 1.0 index to 0.6 ± 0.4 index) and positivity rates (EBV VCA: 38/185 [20.5%] to 5/185 [2.7%]; HSV: 92/185 [49.7%] to 5/185 [2.7%]). These changes notably altered the clinical interpretation of the EBV status, reclassifying the 46 patients previously identified as having primary EBV infection. Our findings indicate a high prevalence of heterophile antibody interference in routine IgM testing for common viruses. HBT pretreatment effectively eliminated this interference and may be valuable for resolving discrepancies in clinical laboratory results.

In this study, we examined heterophile antibody interference in viral serology and evaluated the effectiveness of blocking tubes. Heterophile antibodies markedly increased false‐positive EBV VCA IgM results, leading to apparent active infection; pretreatment with blocking tubes resolved much of this interference. It also converted numerous HSV IgM cases from positive to negative, highlighting the broad applicability of heterophile blocking tube.