Long-term stability studies on the WHO IRP for thromboplastin (human plain BCT/253).

Long-term stability studies on the WHO second primary International Reference Preparation (IRP) for thromboplastin (human plain BCT/253) stored at -20 degrees C have been conducted for ten years. Three centres took part in the exercise using frozen normal and coumarinised plasma samples which were tested throughout. There has been no measurable change in the prothrombin time performance of the human plain IRP over the ten-year period. It can therefore be concluded that new IRP may continue to be calibrated against this preparation in accord with WHO recommendations.