A New, Rapid And Sensitive Determination Of Fibrinopeptide- A (FPA) By A High Affinity Antibody To FPA Antiserum

The clinical relevance of the determination of FPA is not yet fully recognized because of the still time consuming radioimmunological techniques. Shortening of the incubation times allways lead to a critical loss of the sensitivity of the assay. We present now a modification which provides highly sensitive and reproducable results within 2hrs.The ethanolic extraction of FPA from plasma was shortened to 20 min including centrifugation. Samples were analysed in triplicates and evaporated at 50°C on microtiter plates. The addition of 0.2μl normal rabbit serum (NRS) lead to a 20% increase of the reaction rate of the FPA antiserum to FPA. A second antibody with high affinity to rabbit immunglobulin i.e. the FPA antiserum improved the maximal binding to 35% after an incubation period of only 10 min. 35-40000 cpm tracer FPA were added to each sample. FPA antiserum, second antibody and NRS were preincubated for 1-24 hrs and then added together with the tracer to the samples. Thus a sensitive standard curve was obtained between 0.16 and 160 ng/ml (12000-600 cpm). The correlation coefficient of this modification to our previously described method was r=0.96 (n=60) The variation coefficient could be improved substantially to 3.1 for low, 4.0 for medium and 4.5% for high FPA. Normal FPA were measured between 0.16 and 2.5 ng/ml (mean 1.4 ng/ml, n=32).The presented modification of the radioimmunological determination of FPA overcomes the difficulties of previously described methods and provides acurate results within 2 hrs.