What pre-analytical factors can cause spurious prolongation of PT and aPTT?

• A. Improper citrate ratio (bleed-to-citrate 9:1), delayed processing, incorrect sample handling, hemolysis, lipemia, and temperature effects
• B. Hemoglobin measurement errors
• C. Recent electrolyte abnormalities
• D. Using ideal citrate ratio and immediate processing

Answer: (A)

The main idea is that PT and aPTT are highly susceptible to pre-analytical conditions because these tests measure how long clotting takes under carefully controlled conditions, starting with proper anticoagulation and intact plasma. If the blood-to-citrate ratio in the collection tube is off, the amount of anticoagulant available to the sample is not what the test expects, which can skew the calcium balance and the inhibitor environment used during analysis, leading to artificially lengthened clotting times. Delayed processing gives time for clotting factors to degrade, for activation events to occur in the sample, or for the plasma to become unsuitable for accurate measurement, all of which can prolong the observed times. Improper sample handling—such as inadequate mixing or partial clots forming before the test—can introduce artifacts that make clotting appear slower. Hemolysis releases substances that interfere with the assay reagents or the optical detection used to measure clotting, while lipemia causes turbidity that disrupts the measurement and can falsely extend clotting times. Temperature deviations during collection, transport, or storage can slow enzymatic reactions or destabilize factors, both of which can yield protracted results.

In short, these pre-analytical factors directly alter the conditions under which PT and aPTT are measured, producing spurious prolongation. Choice describing only measurement errors in something like hemoglobin, or proposing electrolyte abnormalities as a preanalytical cause, does not capture these common pre-analytical pitfalls. And aiming for an ideal citrate ratio with immediate processing would minimize, not cause, such prolongation.