In vitro stability of human fibrinopeptide B

In anticipation of a future clinical application of plasma fibrinopeptide B (FPB) measurement, we studied the stability of FPB in an ultrafiltrate of normal plasma, normal urine and alkaline buffer by measuring the immunoreactivity of the peptide by FPB radioimmunoassay using anti FPB serum (R-29). FPB was unstable in an ultrafiltrate of plasma and urine and demonstrated a temperature dependent loss of activity. In plasma ultrafiltrate the loss of immunoreactivity was not significant during the first 24 hours, however, 92% of the peptide activity was lost at the end of seven days at 25 degrees C and 37 degrees C. The rate of FPB degradation in urine was comparable. The peptide was stable in an alkaline buffer (pH 8.5) at temperatures ranging from -10 degrees C to 37 degrees C or in plasma ultrafiltrate or urine when incubated at -10 degrees C. Treatment with carboxypeptidase B or leucine aminopeptidase for two hours at 37 degrees C (enzyme/substrate molar ratio of up to 1:100) did not cause a loss of FPB immunoreactivity. EDTA (1.0 mM) and Trasylol (500 units/ml) completely stabilized the peptide in a plasma ultrafiltrate.