A Prolonged aPTT Ahead of an Otherwise Normal Screen

An adult citrate-plasma specimen is collected at 09:10 for preprocedure screening. The tube is filled to the manufacturer line, mixed gently, and received in the laboratory at 09:24. It is not hemolyzed, icteric, lipemic, or clotted. Testing begins at 09:38 on an optical clot detector, using local clot-based PT, activated partial thromboplastin time (aPTT), thrombin time (TT), and Clauss fibrinogen methods.

The results come back as PT 12.1 seconds against the local interval of 10.5 to 13.5 seconds, with an INR of 1.0. TT is 16.8 seconds against 14.0 to 21.0 seconds, and Clauss fibrinogen is 318 mg/dL against 200 to 400 mg/dL. Every one of those sits inside its interval. The aPTT alone is flagged high at 68.4 seconds against 24.0 to 36.0 seconds, timestamped 09:39. A heparin-calibrated anti-Xa drawn from the same specimen returns 0.58 IU/mL, with no local therapeutic interval supplied.

Before you reach for a diagnosis, stop and look at the pattern itself. One result is out of range and the rest are unremarkable. That single fact does not tell you whether this is a missing factor, an inhibitor, a drug effect, or something about how the tube was drawn. Reading that pattern honestly means applying the same cell-based model and reagent logic every time a screen comes back this way.

An isolated prolonged aPTT is a starting question, not an answer.