STEROID RADIOIMMUNOASSAYS: THE PROBLEMS OF BLANKS

Abstract

An estrogen radioimmunoassay was used to study the problem of blanks in steroid assays. Negligible binding (1.5%) in the non-antibody tubes prevailed throughout the study. The assay was validated using accepted procedures. Both water and solvent blanks had estrogen concentrations of 7–9 pg/tube. However, neither water nor solvent blanks showed a dose-related response, indicating that they were "real" blanks. Exogenous estradiol, when added to water and solvent in quantities less than the estimated blank, was not quantitatively recovered. However, exogenous estradiol added to the water solvent in quantities greater than the blank estimate was quantitatively recovered. The sensitivity of the reference standard curve was 6–10 pg/tube, approximately the same as the blank estimate. These results indicated that the estimates of water and solvent blanks were measures of the assay sensitivity. In such circumstances, it is suggested that blank estimates should not be subtracted from sample values. If the blank estimates are high, attention should be directed towards improving the sensitivity of the assay.