A NEW ASSAY FOR BETA-THROMBOGLOBULIN IN URINE

Measurements of beta-thromboglobulin (beta-TG) excretion in urine may be of value for "field" studies and due to problems with sampling artifacts for beta-TG in plasma. Previous studies have used a radioimmunoassay designed for plasma without characterizing the "beta-TG" immunoreactivity in urine. We describe modifications of the assay which increase its sensitivity and a sample work-up procedure using Sephadex G-25M columns separating high molecular weight (HMW) components (presumably intact beta-TG) from low molecular weight (LMW) immunoreactivity (i.e. beta-TG fragments and/or non-specific interferences). The sensitivity of the assay (with 2.5 ml sample) is < 12 pg/ml HMW beta-TG. Inter- and intraassay coefficients of variation were 7-10%. Only 33 (range 5-75)% of beta-TG immunoreactivity in urine represented HMW beta-TG. LMW immunoreactivity may be related to salt and other non-specific influences in the sample. Recoveries of beta-TG were quite variable (9-100%) in unextracted urines, but high and reproducible (80 +/- 2%) in the HMW fraction. Thus, nonspecific interferences with beta-TG measurements in certain urines are overcome by the separation step. Using Sephadex fractionation beta-TG immunoreactivities in night urines (n = 15) were: 20 +/- 3 pg/ml in the HMW fraction, 70 +/- 8 pg/ml in the LMW fraction, and 85 +/- 10 pg/ml by direct assay. HMW beta-TG increased in daytime samples (to 30 +/- 5 pg/ml; p < 0.01), but no diurnal variation was seen in the LMW fraction or with the direct assay. Thus, selective analysis of HMW beta-TG in urine circumvents problems with nonspecific immunoreactivity and apparent interferences with measurements of intact beta-TG. The present more selective assay for HMW immunoreactivity increases the possibility of detecting physiological changes in beta-TG release in vivo by urinary measurements.