SELECTING HUMAN CHORIONIC-GONADOTROPIN IMMUNOASSAYS - CONSIDERATION OF CROSS-REACTING MOLECULES IN 1ST-TRIMESTER PREGNANCY SERUM AND URINE

OBJECTIVE: We investigated the variation in human chorionic gonadotrop in results found with different commercial kits. Levels of human chori onic gonadotropin and related molecules were determined in pregnancy s erum and urine and compared with the specificities of different labora tory, office, and home test kits. STUDY DESIGN: Total human chorionic gonadotropin (nicked + nonnicked), nonnicked human chorionic gonadotro pin, free beta subunit, and beta core fragment were measured in 242 se rum samples and 125 urine samples from early pregnancies. RESULTS: In serum, in the 2 weeks after the missed period when most pregnancy test s are performed, median levels of total, nonnicked, and beta human cho rionic gonadotropin (total + free beta + beta core) were similar (less -than-or-equal-to 12% difference). Individual values, however, varied significantly. For nonnicked human chorionic gonadotropin, values rang ed from 41% to 145% and for beta from 101% to 145% of the total human chorionic gonadotropin level. In urine individual nonnicked values var ied from < 1% to 148% and beta values from 102% to 547% of the total h uman chorionic gonadotropin level. A survey of 29 kits revealed that 1 0 were types detecting total human chorionic gonadotropin, five detect ing nonnicked only, and 14 were beta assays. CONCLUSIONS: Results from total, nonnicked, and beta human chorionic gonadotropin kits are not necessarily interconvertible. Individual variations in levels of nicke d human chorionic gonadotropin, free and beta core, and differences in their recognition by immunoassays causes discordant results.