Functional Platelet Counting in Patients with Renal, Haematological and Cardiological Disease Using Blood Collecting Bottles Coated with Collagen, Ristocetin and Arachidonic Acid.

Platelet function is a vital factor in preventing bleeding irrespective of circulating platelet number. As a result, patients often have their surgery cancelled due to taking Aspirin or related medications. Similarly, patients bleed in the ITU setting when their counts and humoral coagulation are normal. This raises the concept of exhausted platelets which is often difficult to prove. The availability of a bedside technique which enumerates patients’ "functional" platelets, which is reliable and reproducible, represents a major step forward in determining whether these patients require platelet transfusion. Helena Laboratories, Beaumont, Texas, US have produced blood collection bottles which are coated with platelet agonists equine collagen (C), risocetin (R) or arachidonic acid (AA) in addition to 3.2mg sodium citrate. Our group is the first in Europe to use these bottles in association with point of care testing instrumentation (Horiba ABX Pentra, Chicksands, Beds, England). Samples were taken from normal, renal dialysis, cardiac catheterisation, haematological and ITU patients into K2EDTA and the above bottles and treated identically prior to counting. Samples taken into K2EDTA served as baseline controls whilst free platelets in the synchronously taken agonist samples represented non functional platelets (the normal functional ones having aggregated onto the inside wall of the tube). Data on 54 normal subjects showed that, when using C, only 6.2+/−3.1% of platelets were non functional (NF). Similar figures were found for R and AA. In dialysis patients with eGFR 4–25mls/min (n=32), the R NF% was 58.07+/−17.59%. In a similar group of renal patients on dialysis and Aspirin (n=12), the R NF% was 60.55+/−21.86% which was not statistically different from the non Aspirin group (p=0.955). In cardiac patients, all of whom were on Aspirin, C NF% was 35.23+/−23.12%, AA NF% 51.94+/−23.5% and R NF% 51.53+/−19.04%. C vs AA showed a significant p-value of 0.003and C vs R p=0.002. AA vs R was not significant at p=0.94. These data show that ristocetin is a surprisingly sensitive method of detecting non functional platelets in renal and Aspirin users. Classically, ristocetin is not thought of being a detector of Aspirin effect although data from Sloand et al. JASN (1997) 8(5),799 shows that ristocetin may detect renal effect on platelet GpIb-IX (CD42b). These data demonstrate the potential value of ristocetin aggregation ex vivo in determining the need for platelet transfusion and may provide clinicians with an improved and more logical rationale for such an expensive therapy.