Your Turn: Plan the Next Step and the Message

You are handed a new case built on the same shift. The pattern is an isolated prolonged aPTT, a mixing study with partial immediate correction and worse correction after incubation, and a one-stage FVIII activity that comes back low. No chromogenic FVIII or inhibitor titer has been run yet, and medication reconciliation has not been completed. You need to decide what to order next and what you can and cannot say yet.

The decision has three parts. First, decide which additional test or check would most directly tell you whether the low one-stage FVIII reflects a real deficiency, an interference artifact, or an inhibitor. Second, recognize when a result pattern is not analytically valid, such as a nonparallel dilution series, and what that should trigger instead of a reported number. Third, decide what you can communicate now and to whom, given that an unexplained prolonged aPTT before an invasive procedure or in a new bleeding presentation calls for prompt specialist communication, while the laboratory does not choose the treatment.

Work through the ordering exercise below to put the confirmatory steps in a defensible sequence, then answer the checks that follow. Your first answer is recorded before any retry, so read the case pattern carefully before choosing.

An unexplained isolated prolonged aPTT with a low factor activity is a communication event as much as a testing event; order the workup and notify the right person without waiting for a final diagnosis you are not positioned to make.