Platelet aggregation and ATP release in whole blood for diagnosis of bleeding disorders

Abstract number: P1809

Miller^* C. H., Nix† B., Benson‡ E., Abshire† T. C.

^*Centers for Disease Control & Prevention, USA; ‡Emory Medical Laboratories, Emory Hospital, USA †Emory University School of Medicine, USA;

Platelet aggregation studies performed in whole blood (WB) have technical advantages over those done in platelet-rich plasma (PRP), including a smaller blood volume requirement and minimal sample manipulation. Few direct comparisons of the methods have been done. Split sample analysis was performed on samples from 12 patients undergoing clinical testing for a possible bleeding disorder (cases) and 12 laboratory controls using an optical aggregation in PRP and an impedance method for WB. Comparisons were made using collagen at 2 µg mL^-1, arachidonic acid at 0.5 mM, ADP at 10 nM (PRP) and 20 nM (WB), ristocetin at 1.5 mg mL^-1 (PRP) and 0.75 mg mL^-1 (WB), epinephrine at 10 µM (PRP), and thrombin at 1 U mL^-1 (WB). Established reference ranges for each method were used to classify each result as normal or abnormal. For the 12 controls, using five agonists, 1/57 tests (1.8%) were discrepant between the methods. Among 12 cases, 6/57 tests (10.5%) were discrepant. Abnormal results with multiple agonists were seen in two cases (16.7%) and 1 control (8.3%) by both methods. ADP gave the sole abnormality in two cases in PRP and one in WB. ATP release (ATPR) was measured concurrently in WB by luminescence. Six cases (50%) and two controls (17%) had abnormal ATPR with one or more agonists. ATPR with thrombin was normal in all cases and 11/12 controls. Data were also available on WB aggregation (AGG) and ATPR performed in patients with known platelet function defects. Three patients with Glanzmann's thrombasthenia (GT) showed the expected AGG defect and variable ATPR. Two patients with Hermansky–Pudlak syndrome (HPS) had normal AGG and deficient ATPR. A patient with TAR syndrome was deficient in AGG and ATPR. Patients with various von Willebrand disease subtypes showed the expected defects in ristocetin AGG. In addition, ristocetin AGG was qualitatively abnormal in GT and HPS, showing a pattern of disaggregation. In summary, parallel aggregation tests in WB and PRP gave similar outcomes. ATPR was abnormal in a much larger proportion of cases than was aggregation. In those with known disorders, WB aggregation findings were as expected from PRP, and ATPR gave additional information that would be useful for making the diagnosis in those rare cases.