• Activated partial thromboplastin time (aPTT);
  • Anticoagulant;
  • Canine;
  • One-stage prothrombin time (OSPT);
  • PFA-100

Background:Blood collection tubes containing 3.2% (0.109 M) sodium citrate, instead of 3.8% (0.129 M) sodium citrate, have recently become available in the United States. These tubes are visually indistinguishable from the traditional 3.8% sodium citrate tubes, except for wording on the label. Consequently, samples for hemostatic evaluation are frequently collected in tubes containing the lower concentration of sodium citrate.

Hypothesis:Results of hemostasis assays are different in samples collected in 3.2% versus 3.8% sodium citrate.

Animals:Twenty healthy dogs.

Methods:This study aimed at determining whether results of standard coagulation tests, von Willebrand factor concentration (vWF:Ag), and platelet function with the platelet function analyzer PFA-100a were affected by the different concentrations of sodium citrate. Blood samples were collected in tubes containing either 3.2% or 3.8% sodium citrate concentrations and processed routinely for coagulation assays (one-stage prothrombin time [OSPT], activated partial thromboplastin time [aPTT], fibrinogen concentration, and platelet count), vWF:Ag, and platelet function assays with a PFA-100.

Results:There was no significant difference between samples collected in 3.2% versus those collected in 3.8% sodium citrate for OSPT, aPTT, fibrinogen concentration, platelet count, or vWF:Ag. The closure times with collagen/adenosine diphosphate were significantly shorter (66 ± 8.1 versus 74.8 ± 9.7 seconds; P < .0001) with the 3.2% than with 3.8% sodium citrate concentration, and the hematocrit was significantly higher (47.9 ± 5.6 versus 46.0 ± 4.7 seconds; P= .03) in samples collected in 3.2% than in those collected in 3.8% sodium citrate.

Conclusions and Clinical Importance: There is no clinically relevant effect of collection of blood into 3.2% or 3.8% sodium citrate.