the effect of recombinant tissue plasminogen activator (r-tpa) on quantitation of neutralising anti-streptokinase antibodies

the measurement of anti-streptokinase antibodies can distinguish the patients who may benefit from streptokinase and those who should be treated with some other thrombolytic regimen. neutralising titration test is a commonly used classical assay for measuring anti-streptokinase antibodies and in this assay the ability of anti-streptokinase antibodies in patients' sera in preventing the lytic effect of streptokinase is assessd. as we showed previously the presence of r-tpa in the serum may interefere with the neutralising titration test, we investigated this interference in vitro. the level of neutralising anti-streptokinase antibodies in a serum sample with known levels of the antibodies were measured in absence and presence of increasing amount of r-tpa including therapeutic values. increasing amount of r-tpa in vitro induced a sudden reduction in the measurable titre of anti-streptokinase antibody levels in a serum with elevated levels of anti-streptokinase antibodies. this effect of r-tpa, which is through activation of plasminogen has not been reported previously. we suggest this assay is unsuitable for clinical diagnosis of anti-streptokinase antibodies.