Urine Beta-Thromboglobulin Concentration or Beta-Thromboglobulin/Creatinine Ratio in Single Voided Urine Samples Cannot Be Reliably Used to Estimate Quantitative Beta-Thromboglobulin Excretion

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.

Effect of acetyl salicylic acid on increased production of thromboxane after aortic graft surgery

Contact between blood and foreign surfaces, e.g. vascular grafts, causes activation and release of platelets. One consequence of platelet activation is production of thromboxane A2 (TxA2). The physiological effects of TxA2, i.e. platelet aggregation and vaso-constriction are counteracted by another prostanoid, prostacyclin (PGI2). Acetylsalicylic acid (ASA) causes a longlasting inhibition of platelet TxA2 production and a more shortlasting inhibition of PGI2 production. The present study examines TxA2 and PGI2 synthesis in patients receiving synthetic arterial grafts, some of which were treated with ASA. The prostanoid synthesis was evaluated by measurement of their main urinary metabolites with gas chromatography-mass spectrometry. Platelet release was evaluated by measurements of beta-thromboglobulin (beta-TG) and the plasma coagulation by measurements of fibrinopeptide A (FPA). These compounds were also measured in urine in order to avoid artifacts caused by activation of platelets and plasma coagulation during blood sampling. Following replacement of the abdominal aorta with a synthetic vascular graft there was a marked increase in the synthesis of TxA2 and PGI2. Increased levels of beta-TG and FPA were also demonstrated. Administration of ASA on the first and second postoperative days significantly reduced the synthesis of TxA2 but caused no significant effects on the other parameters measured. It is concluded that ASA may be beneficial in the postoperative period since it counteracts TxA2 with vasoconstricting and platelet aggregating properties but leaves PGI2 with vasodilating and antiaggregating properties relatively uneffected.

Interaction between platelets and lupus anticoagulant

10 consecutive patients fulfilled the diagnostic criteria for lupus anticoagulant. 4 had concomitant systemic lupus erythematosus, 1 Waldenstrom's disease and 5 had no apparent underlying disease. Only the case with Waldenstrom's disease presented a bleeding tendency, with bleeding time greater than 20 min; the others had a history of thrombotic complications. A defect of platelet aggregation induced by ADP, epinephrine, collagen and arachidonic acid was documented in the Waldenstrom's disease case whose lupus anticoagulant was an IgM. In the others, lupus anticoagulant, identified as IgG immunoglobulins, produced no aggregation abnormalities. However, beta-thromboglobulin levels in platelets, plasma and urine were consistent with a pattern of platelet activation in all cases. IgG immunoglobulins separated from sera of 6 patients showed lupus anticoagulant activity, with no effects on platelet aggregation of normal platelet-rich plasma, but they induced secretion of beta-thromboglobulin from normal platelets.