Monitoring treatments with unfractionated heparin: CTAD must be used instead of citrate as the anticoagulant solution when using partial-draw collection tubes. Results of a multicenter evaluation

Background: Sampling small volumes of blood may be necessary, particularly in pediatric patients, or in case of difficult or recurrent venipunctures.

Methods: Routine hemostasis test results evaluated in partial- and full-draw evacuated polymer tubes obtained in 4 centers were compared.

Results: No relevant discrepancy (Bland-Altman) was found between test results measured in partial- and full-draw tubes obtained from untreated patients and from patients on vitamin K-antagonist or low molecular weight heparin. In patients on unfractionated heparin (UFH), significantly lower anti-FXa activity [median=0.29IU/mL (range:0.04-1.15) vs. 0.39 (0.05-1.25), n=89, p<0.0001] and shorter aPTT were measured in partial-draw tubes. This discrepancy was likely to be related to the release of higher amounts of PF4 after increased platelet activation in partial-draw tubes. As CTAD is known to counteract platelet activation, we then collected blood into partial-draw CTAD tube and full-draw citrate tube. Both in patients on UFH and in untreated patients, no relevant difference could be demonstrated for all studied parameters (Bland-Altman), including aPTT and anti-FXa activity, even if analytical comparison showed significantly higher anti-FXa activity in partial-draw CTAD than in full-draw citrated tubes with a mean bias of 0.02 IU/mL, identical throughout the measuring range.

Conclusions: These results suggest that samples collected into partial-draw citrate tubes allow accurate routine coagulation testingin all patients but those requiring UFH assessment,in which their use led to a significant underestimation ofanticoagulation. In such cases, partial-draw tubes containing CTAD could be validly used to monitor heparin therapy as well as to perform routine coagulation testing.