Effects of sodium citrate. low molecular weight heparin, and prostaglandinE-1 on aggregation, fibrinogen binding, and enumeration of equine platelets

Objective-To investigate the effects of sodium citrate, low molecular weigh t heparin (LMWH), and prostaglandin E-1 (PGE(1)) on aggregation, fibrinogen binding, and enumeration of equine platelets. Sample Population-Blood samples obtained from 4 Thoroughbreds. Procedure-Blood was collected into syringes in the ratio of 9 parts biood:1 part anticoagulant. Anticoagulants used were sodium citrate, LMWH, sodium citrate and LMWH, or 300 nM PGE(1)/ml of anticoagulant. Platelet aggregatio n in response to ADP, collagen, and PGE1 was assessed, using optical aggreg ometry. Platelet activation was evaluated, using flow cytometry, to detect binding of fluorescein-conjugated anti-human fibrinogen antibody. Plasma co ncentration of ionized calcium was measured, using an ion-selective electro de. Results-Number of platelets (mean +/- SEM) in samples containing LMWH (109. 5 +/- 11.3 x 10(3) cells/mul) was significantly less than the number in sam ples containing sodium citrate (187.3 +/- 30.3 x 10(3) cells/mul). increasi ng concentrations of sodium citrate resulted in reductions in platelet aggr egation and plasma concentration of ionized calcium. Addition of PGE, prior to addition of an agonist inhibited platelet aggregation in a concentratio n-dependent manner, whereas addition of PGE, 4 minutes after addition of AD P resulted in partial reversal of aggregation and fibrinogen binding. Conclusions and Clinical Relevance-A high concentration of sodium citrate i n blood samples decreases plasma concentration of ionized calcium, resultin g in reduced platelet aggregation and fibrinogen binding. Platelets tend to clump in samples collected into LMWH, precluding its use as an anticoagula nt. Platelet aggregation and fibrinogen binding can be reversed by PGE(1), which may result in underestimation of platelet activation.