Evaluation of a citrate-based anticoagulant with platelet inhibitory activity for feline blood cell Counts.

Aggregation of feline platelets in vitro results in difficulty assessing platelet number. A citrate-based anticoagulant containing the platelet inhibitors theophylline, adenosine, and dipyridamole (CTAD; Diatube-H, Becton Dickinson, Oxford, UK) has been developed for use in human platelet studies and heparin assays. To evaluate the efficacy of CTAD in reducing platelet aggregation in feline blood samples, aliquots of blood from 51 cats were anticoagulated with EDTA, CTAD, and for 12 samples, citrate solution. Samples preserved in CTAD had significantly higher (P</=.001) platelet counts, as determined by an impedance counter, hemacytometer, and smear estimation, than samples preserved in EDTA. In addition, subjective assessment of blood smears showed significantly fewer platelet aggregates (P<.001) in CTAD-treated samples compared with EDTA samples. Although values were similar, automated platelet counts and smear estimates of platelet number were significantly higher (P<.05) and platelet aggregation was significantly less (P<.05) in CTAD samples than in citrate samples. These results suggest that the platelet inhibitory activity of CTAD reduced feline platelet aggregation. Automated total WBC counts in CTAD samples were significantly lower (P<.001) than automated counts in EDTAsamples but were similar to manual WBC counts in EDTAsamples. Differences in both platelet and WBC counts between CTAD and EDTA or citrate samples were clinically relevant. Mean platelet volume and MCV were significantly lower (P<.05) in CTAD samples than in EDTA samples. No effect was seen on cell morphology or staining characteristics. The anticoagulant CTAD offers an advantage over both EDTA and cit-rate for feline hematologic analysis, by decreasing pseudothrombocytopenia and pseudoleukocytosis.