Easy fix for clinical laboratories for the false-positive defect with the Abbott AxSym total β-hCG test

Abstract

Background: False-positive hCG results can lead to erroneous diagnoses and needless chemotherapy and surgery. In the last 2 years, eight publications described cases involving false-positive hCG tests; all eight involved the AxSym test. We investigated the source of this abundance of cases and a simple fix that may be used by clinical laboratories. Methods: False-positive hCG was primarily identified by absence of hCG in urine and varying or negative hCG results in alternative tests. Seventeen false-positive serum samples in the AxSym test were evaluated undiluted and at twofold dilution with diluent containing excess goat serum or immunoglobulin. Results: We identified 58 patients with false-positive hCG, 47 of 58 due to the Abbott AxSym total hCGβ test (81%). Sixteen of 17 of these “false-positive” results (mean 100 mIU/ml) became undetectable when tested again after twofold dilution. Conclusions: A simple twofold dilution with this diluent containing excess goat serum or immunoglobulin completely protected 16 of 17 samples from patients having false-positive results. It is recommended that laboratories using this test use twofold dilution as a minimum to prevent false-positive results.