Falsely decreased human chorionic gonadotropin (hCG) results due to increased concentrations of the free beta subunit and the beta core fragment in quantitative hCG assays.

BACKGROUND: Earlier studies have shown that increased concentrations of certain human chorionic gonadotropin (hCG) variants can cause false-negative results in some qualitative hCG devices. The objective of this study was to determine if increased concentrations of hCGß and hCGß core fragment (hCGßcf) cause falsely decreased results on 9 commercially available quantitative hCG assays. METHODS: Several concentrations of purified hCGß and hCGßcf were added to 2 sets of 6 serum samples with and without a fixed concentration of intact hCG. We examined 9 widely used immunoassays to measure immunoreactive hCG. Falsely decreased results were defined as those in which the measured hCG concentration was ≤50% of expected. RESULTS: High concentrations of hCGß (≥240 000 pmol/L) produced falsely decreased hCG measurements in 2 assays known to detect this variant. Similarly, high concentrations of hCGßcf (≥63 000 pmol/L) produced falsely decreased hCG measurements in 3 assays that do not detect purified hCGßcf. Two assays were identified that detected both hCGß and hCGßcf, and neither produced falsely decreased results in the presence of high concentrations of these variants. CONCLUSIONS: Extremely high concentrations of hCG variants can cause falsely decreased results in certain quantitative hCG assays. Of the 9 assays examined, none exhibited falsely decreased results in the presence of hCGß concentrations typically associated with hCGß-producing malignancies. Two assays exhibited decreased (>50%) hCG results in the presence of hCGßcf concentrations found during normal pregnancy.