ARE DISCARD TUBES NECESSARY IN COAGULATION STUDIES

We evaluated the necessity of drawing a discard tube on prothrombin ti me (PT) and activated partial thromboplastin time (APTT) results in ou tpatients taking oral anticoagulant therapy. We drew two blue-stoppere d tubes on 380 patients rather than the traditional practice of fillin g a red-top tube before filling the coagulation tube. We ran PTs and A PTTs on both samples and compared results. We evaluated two sodium cit rate concentrations and two prothrombin reagents, one sensitive and th e other less sensitive. When PT results are reported as international normalized ratio values, no statistically significant difference exist s in values between the first and second tubes filled regardless of re agent sensitivity or citrate concentration. We measured APTTs using tw o citrate concentrations and a factor-sensitive APTT reagent. Similarl y, APTT results showed no significant difference between tubes.