Measurement of inaccuracy and imprecision of HCG methods using dilutions of the WHO 4th IS-HCG standard and a pregnant patientʹs serum

Introduction: Differences in human chorionic gonadotropin (hCG) results obtained by seven different methods were documented by analyzing dilutions of the WHO 4th International Standard (IS) and a pregnant patientʹs serum. Materials and methods: Biases of +30.9 to −37.5% and +36.8 to −36.1% from the target concentration were found for the WHO 4th IS and patient sample dilutions, respectively. Results: Imprecision was calculated from replicate measurements of hCG on the different sample dilutions. Imprecision ranged from 1.0% to 18.9% and 1.1% to 5.3% for the WHO 4th IS and patient sample dilutions, respectively. Using a maximum allowable error of 12.5% for hCG measurements, we found that two instruments were so biased that their hCG measurements could not be interchanged with hCG values produced by any of the other systems. Discussion: It is ideal to use only one hCG methodology for the serial monitoring of hCG; otherwise, hCG methods should be carefully chosen to minimize inter-method bias.