Race-ethnicity-specific variation in multiple-marker biochemical screening: alpha-fetoprotein, hCG, and estriol

To identify any race-ethnicity-specific differences in serum alpha-fetoprotein (AFP), hCG, and unconjugated estriol (E3) levels in women between 14 and 21 weeks' gestation.

Data from the 3-year period 1992-1994 were analyzed from 208,257 women who had AFP screening, of whom 155,142 also had hCG and 62,121 also had E3 screened, between 14 and 21 weeks' gestation. Subjects were categorized into four groups: white, black, Asian, and Hispanic.

There was a consistent pattern of analyte differences across gestational ages. Levels for AFP were generally higher in Asian and black women than in Hispanic and white women (median AFP at 16 weeks-31.2, 30.9, 27.4, 27.3, respectively), and levels of hCG and E3 were highest in Asians (hCG at 16 weeks-34.7, 30.3, 28.2, 26.8, respectively). Weight correction for AFP, hCG, and E3 levels did not compensate for the ethnic differences.

Because hCG and E3 demonstrate the same general pattern of differences as AFP among ethnic groups, averaging values for all ethnic groups tends inappropriately to lower calculated Down syndrome risks for black and Asian women. Additionally, the slopes of the curves are not parallel, such that separate data bases are preferable to multiplicative correction factors. Separate data bases should be used in laboratories with volume sufficient to permit the establishment of race-ethnicity-specific regressions. Use of separate data bases should result in more accurate screening.