Key result
Underfilling citrate tubes below 90% capacity yields falsely elevated PT and APTT results.
Why the study?
Underfilling of specimen tubes containing 129 mmol/L (3.8%) buffered citrate prolongs PT and APTT values, but the effect with 109 mmol/L (3.2%) buffered citrate was unclear.
Does underfilling specimen tubes with 3.2% citrate anticoagulant affect the accuracy of PT and APTT values in healthy subjects and patients on warfarin?
Population
12 healthy subjects and 30 patients on long-term warfarin therapy
Comparison
Underfilled specimen tubes (52% to 100% capacity) vs fully filled tubes
Design
Experimental study with blood samples from subjects and patients
Authors
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Caution against underfilled 3.2% citrate tubes for PT/APTT; extends 3.8% data but leaves optimal fill thresholds open.
Does underfilling specimen tubes with 3.2% citrate anticoagulant affect the accuracy of PT and APTT values in healthy subjects and patients on warfarin?
Specimen tubes containing 3.2% citrate must be filled to at least 90% of capacity to avoid falsely elevated PT or APTT results, particularly for patients on warfarin therapy.
Reneke et al. (1998) studied Healthy subjects and patients on warfarin therapy (n=42). Underfilling of specimen tubes with 109 mmol/L (3.2%) citrate vs. Adequately filled tubes was evaluated on Accuracy of prothrombin time (PT) and activated partial thromboplastin time (APTT). Specimen tubes with 3.2% citrate must be filled to at least 90% of capacity to avoid falsely elevated PT or APTT results, though normal specimens may yield accurate PTs at 65% capacity.
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