Standardization of methods reduces variability: explanation for historical discrepancies in biochemical screening.

Over the past decade, many studies have argued the relative merits of different chromosome abnormality biochemical screening protocols in different labs. Results and interpretations have varied markedly (e.g., double vs. triple screening). In this study we sought to compare coefficients of variation (CV) among 12 laboratories in one system, using identical and different methodologies for the three parameters. Ten identical specimens were processed as part of the 1999 College of American Pathologists (CAP) (FP-A, FP-B) proficiency tests. Results were compared among 12 laboratories using the Abbott ELISA for alpha-fetoprotein (AFP) and human chorionic gonadotropin (hCG), and two methods for estriol [Diagnostic Services Laboratory (DSL) and an "in house" assay]. The range on the 10 specimens of means for AFP varied from 12.56 to 117.87; hCG 14.05-68.08; and estriol 0.61-2.73. CV for AFP specimens averaged 10%, hCG 8%, and estriol 35% (F = 22.4). However, when only DSL was used for estriol, the CV was reduced to 8.7%. Standardization of AFP and hCG across 12 labs has reduced CV to <10%, which is similar to accepted between run results. Wide variation of uE3 among different methods may explain the widely divergent results in the literature. With national standardization of all parameters, the widely divergent results seen in the literature should narrow, and regional medians will no longer be necessary.