A short-filled tube and a flagged coagulation panel

A butterfly draw comes back from an outpatient visit with a prothrombin time (PT) of 16.8 seconds and an activated partial thromboplastin time (aPTT) of 43.6 seconds, both above the laboratory's teaching reference interval of 10.0 to 13.0 s and 25.0 to 35.0 s. Before you call this a bleeding risk, look at the collection record. The citrate tube was the first tube connected to the butterfly tubing, the local discard step was skipped, and the tube filled to only 1.8 mL against a 2.7 mL fill line. The collection time is documented as 09:12.

Nothing about the analyzer, the reagent, or the patient tells you this result is wrong. The clue is upstream, in how the specimen was built. A short-filled citrate tube changes the ratio of blood to citrate anticoagulant that the coagulation assay assumes, and a prolonged clot-based result from that tube cannot be read as evidence of the patient's coagulation state.

The decisions that happen before a tube ever reaches an analyzer determine whether the result can be trusted: which additive goes first, which specimens need a discard tube or a timed clock, which need to be kept cold, warm, or dark, and what to say and document when a collection does not go as ordered.

When a chemistry or coagulation result looks wrong, check the collection record before you second-guess the analyzer.