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.