Comparison of 2 commercially available human chorionic gonadotropin immunoassays used in the management of gestational trophoblastic neoplasia.

OBJECTIVE To compare serum human chorionic gonadotropin (hCG) titers using 2 commercially available hCG immunoassays in patients with gestational trophoblastic neoplasia (GTN). STUDY DESIGN A total of 213 serum samples from 39 patients with uneventful moles and 697 serum samples from 17 patients with low-risk and high-risk GTN were obtained and subsequently measured with both the hCG C-terminal (hCG-CTP) and DPC Immulite 2000 tests. RESULTS In patients with uneventful moles and GTN, serum hCG levels recorded using the hCG-CTP and DPC Immulite 2000 tests correlated well (r2 = 0.936 and r2 = 0.958). However, the serum hCG titers measured using the DPC Immulite 2000 assay were approximately 2.5- and 2.7-fold higher than those measured with the hCG-CTP test (p < 0.0001) when lower titers of hCG (< 40 mIU/mL) were tested. In addition, 3 and 1 patient, respectivelyl, with uneventful mole and GTN obtained positive results with the DPC Immulite 2000 test (3.0-4.2 mIU/mL) after demonstrating undetectable hCG levels with the hCG-CTP test (< 1.0 mIU/mL). CONCLUSION At the lower levels of hCG, a few discrepancies between hCG titers measured using the 2 commercial immunoassays arose and may be attributed to the existence of hCG-related molecules. However, these hCG metabolites disappeared rapidly, the clinical importance of which remains unclear.