Heterophile antibody interference in qualitative urine/serum hCG devices: Case report

Objectives: This case report investigates the origin of a false positive result on a serum qualitative human chorionic gonadotropin (hCG) device. Patient and methods: A 46-year-old woman diagnosed with chronic myeloid leukemia presented with nausea and vomiting. A qualitative serum hCG test was interpreted as positive; however, a quantitative serum hCG test was negative (<. 5 IU/L). To further investigate this discrepancy, the sample was pretreated with heterophilic blocking reagent (HBR). Additionally, the sample was tested on other qualitative hCG devices composed of antibodies from different animal sources. Blocking reagent from an automated quantitative immunoassay was also tested for its ability to inhibit the heterophile antibody interference. Results: The qualitative test result was negative after pretreatment with heterophilic blocking reagent. Other devices composed of antibodies from different animal sources also demonstrated mixed results with the patient's sample. Blocking reagent obtained from the automated quantitative assay inhibited the heterophile antibody interference in the patient's sample. Conclusion: This case demonstrates that positive serum point-of-care hCG results should be interpreted with caution and confirmed with a quantitative serum hCG immunoassay when clinical suspicion is raised.