RAPID, AUTOMATED QUANTIFICATION OF TOTAL HUMAN CHORIONIC-GONADOTROPININ SERUM BY A CHEMILUMINESCENT ENZYME IMMUNOMETRIC ASSAY

Total human chorionic gonadotropin (hCG-hCG beta) in serum was assayed with the Immulite system, a fully automated random-access immunoassay analyzer that has a unique centrifugal procedure for solid-phase wash ing and a chemiluminescent detection system. The broad range of the hC G calibration curve (up to 5000 IU/L) is achieved by using a small ser um sample size (5 mu L), which provides sufficient volume for low-end sensitivity and prevents the possible high-dose hook effect in the wor king range of the assay. Within-run imprecision (CV) ranged from 3.9% to 5.9% for hCG between 10.5 and 2908 IU/L. Between-run imprecision ra nged from 8.8% to 12.7% for hCG mean concentrations from 11.4 to 88.4 IU/L. The antibodies used in the Immulite hCG assay system gave little or no interferences when high amounts of follitropin, lutropin, and t hyrotropin were added. A complete recognition of the free beta-subunit of hCG was obtained (+/- 180%). In sera from women with molar pregnan cies, we observed no high-dose hook effect at hCG concentrations up to 3000 klU/L. The broad range of hCG concentrations encountered through out normal pregnancy (up to 200 klU/L) requires an extended working ra nge to avoid high dilutions. In early pregnancy, accuracy in the range of 1000-5000 IU/L is enhanced by avoiding dilutions.