Rapid Radioimmunoassay For Fibrinopeptide A In Human Plasma

Abstract

The originally-described method for assay of fibrino- peptide A (FPA) in human plasma includes alcohol precipitation and dialysis steps which are complex, time consuming, and limit the applicability of the assay. The purpose of this work was to devise an assay for FPA which could be more easily applied to clinical studies, and to use this assay to study some of the factors which might cause artefactual results on blood samples obtained from patients. A rapid method for FPA assay has been developed which is simple, robust and sensitive and allows results to be obtained within 2.5 hrs. of blood collection. The assay depends on the use of bentonite to absorb fibrinogen from plasma, and gives a normal range for plasma FPA (0.3 - 1.5 pmol/ml) which is similar to that measured using the originally-described method. There is an equally good correlation between results obtained by the two methods on samples obtained from patients with various levels of circulating FPA and/or fibrinogen/fibrin degradation products (FDPs). Following venepuncture, FPA levels in sequential samples of blood drawn through 19-gauge ‘Butterfly’ needles became progressively lower in successive samples, indicating that a larger than usual discard of blood is necessary if basal levels are to be accurately assessed. Different antisera showed differences in affinity for FPA and cross reaction with des amino tyrosyl FPA, but such differences are unlikely to cause problems when assaying clinical samples. Generation of FPA from whole blood in vitro is completely suppressed by heparin/Trasylol anticoagulant in conventionally-used concentration, and we therefore find no evidence in favour of the suggestion that this anticoagulant mixture is unsuitable for sample collection for FPA assay.