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Heterophile antibody interference in qualitative urine/serum hCG devices: Case report
Khushbu K Patel1, Ann M Gronowski1
1Department of Pathology and Immunology, Washington University School of Medicine, St. Louis, MO, USA.
Insights
A false positive serum human chorionic gonadotropin (hCG) test in a leukemia patient was caused by heterophile antibodies. Confirmation with quantitative hCG testing is crucial when clinical suspicion arises.
Area of Science:
- Clinical Chemistry
- Immunodiagnostics
- Point-of-Care Testing
Background:
- Heterophile antibodies can interfere with immunoassays, leading to inaccurate results.
- A case of false positive serum human chorionic gonadotropin (hCG) was observed in a patient with chronic myeloid leukemia.
Observation:
- A qualitative hCG test yielded a positive result, but a quantitative test was negative.
- Pretreatment with heterophilic blocking reagent (HBR) and testing on different qualitative hCG devices revealed interference.
- Blocking reagent from an automated quantitative immunoassay successfully inhibited heterophile antibody interference.
Findings:
- Heterophile antibody interference was identified as the cause of the false positive qualitative hCG result.
- Different qualitative hCG devices showed varied responses due to differing antibody sources.
- The blocking reagent from a quantitative assay effectively neutralized the interfering antibodies.
Implications:
- Qualitative point-of-care hCG tests require cautious interpretation.
- Quantitative hCG assays are essential for confirmation when clinical suspicion is present.
- Understanding immunoassay interference is vital for accurate diagnostic testing.
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 (<5IU/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.
