An assay for rapid factor XIII activity measurement has been developed based on the
determination of the ammonium released during fibrin stabilization. Factor XIII was
activated by thrombin and calcium. Ammonium was measured by an ammonium-sensitive
electrode. It was demonstrated that the assay procedure yields accurate and precise
results and that factor XIII-catalyzed fibrin stabilization can be measured kinetically.
The amount of ammonium released during the first 90 min of fibrin stabilization was
found to be 7.8 ± 0.5 moles per mole fibrinogen, which is in agreement with the findings
of other authors. In 15 normal subjects and in 15 patients suffering from diseases
with suspected factor XIII deficiency there was a satisfactory correlation between
the results obtained by the “ammonium-release-method”, Bohn’s method, and the immunological
assay (r1 = 0.65; r2= 0.70; p<0.01). In 3 of 5 patients with paraproteinemias the values of factor XIII
activity determined by the ammonium-release method were markedly lower than those
estimated by the other methods. It could be shown that inhibitor mechanisms were responsible
for these discrepancies.
Keywords
Factor XIII activity - Inhibitors of fibrin stabilization - Ammonium release - Ammonium-sensitive
electrode
