Is there a reason one might perform a partial thromboplastin time (PTT) mixing study on a patient whose initial PTT result is short (slightly below the reference range)? Since a short PTT time would appear to indicate there isn’t a factor deficiency or a circulating anticoagulant, might there be another reason? I couldn’t find anything in the literature.
Hello, and thank you for your question. No, nothing can be gained by performing a standard mixing study on a shortened PTT. Mixing studies are designed to detect inhibitors or factor deficiencies that prolong the PTT, and are unlikely to provide any information for a shortened PTT.
We’ve always assumed that short prothrombin times (PTs) and PTTs were the consequence of a specimen management error, however I draw your attention to a 2010 article, Lippi G, Salvagno GL, Ippolito L, Franchini M, Favaloro EJ. Shortened activated partial thromboplastin time: causes and management. Blood Coagul Fibrinolysis 2010;21:459-63. that speculates on the possible clinical and physiological causes. While a mixing study doesn’t help, there may be an argument for factor assays that detect, for instance, elevated factor VIII, which could be associated with thrombophilia. Geo.