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 less than 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 less than 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.