In Vitro Characterization of Platelet Dysfunction In Common Hematological Disorders Using the Verify Now^® Assay

Myelodysplastic syndrome (MDS), immune thrombocytopenia purpura (ITP) and myeloproliferative disorders (MPD) are frequent diagnoses in a community hematology practice. Qualitative platelet defects are common features of these disorders but are difficult to characterize in daily practice as specialized technology is not readily available. The Verify Now® (VN) is a rapid, point-of service assay to measure platelet aggregation. VN assesses the degree of inhibition of GPIIb/IIIa mediated aggregation and uses minimal sample preparation. Its main application currently, is to determine the adequacy of anti-platelet therapy with aspirin (ASA), thienopyridines, such as clopidogrel (CPL), and GPIIb/IIIa inhibitors in patients with cardiovascular disease. (Verify Now for IIb/IIIa, aspirin, and P2Y12, Instructions for Use, Accumetrics) We used VN to detect platelet aggregation defects in patients with ITP, MDS and MPD and compared the to a platelet function analyzer PFA -100. (Francis JL; In Michelson AD, ed. Platelets, 2^nded. San Diego: Elsevier/Academic Press, 2007:535-544)

Subjects with MDS, ITP, and MPD were identified from our Hematology practice. Informed consent was obtained from all patients. Patients taking aspirin and /or clopidogrel were not excluded. Platelet function was determined concurrently using VN and PFA-100 using standard reference ranges. (Verify Now for IIb/IIIa, aspirin, and P2Y12, Instructions for Use, Accumetrics), (Mammen EF et al; Semin Throm Hemost. 1998; 24 (2):195-205).

Thirty three patients are enrolled in the study, 21 with ITP, 6 with MDS and 6 with MPD. Assay results are available for 30 patients. Platelet counts for all patients ranged from 2 to 1206 ×10³/cmm, mean platelet count being 184 ×10³/cmm (SD ± 215) and median count was 120 ×10³/cmm.

In 15 patients with ITP and platelet count ≥ 100 ×10³/cmm, 11 were not on ASA/CPL. PFA-100 and VN each detected abnormalities in 4 patients but results were non-concordant in 2 patients. In 4 patients on ASA, VN detected ASA effect in all 4 whereas the PFA-100 detected 2.

In 2 patients with platelet count < 100 ×10³/cmm not on ASA/CPL, VN detected abnormalities in both, whereas PFA detected only 1. (Table 1)

Two patients had counts ≥ 100 ×10³/cmm. One was on ASA and both assays detected ASA effect. Neither assay detected an abnormality in the patient not on ASA.

In 4 patients with counts <100 ×10³/cmm, 3 were not on ASA/ CPL. Both assays detected abnormalities in all 3 and ASA effect in 1 patient on ASA. (Table 2)

In 4 patients with counts < 400 ×10³/cmm, not on ASA/CPL, both assays detected non-concordant abnormalities in 1 patient. Both assays detected CPL and ASA effect in 1 patient taking both drugs.

2 patients had count ≥400,000. In 1 patient taking CPL, VN detected CPL effect but PFA did not. In 1 patient on ASA, PFA detected abnormality but VN did not. (Table 3)

In patients with MDS, ITP, and MPD, abnormal platelet function is common. These results show that VN may be as sensitive for detecting platelet dysfunction as PFA-100. Results were especially concordant in MDS patients. We plan to include 150 patients to confirm these results. We hope to define qualitative platelet defects in this population so that appropriate intervention can be recommended prior to invasive procedures.

No relevant conflicts of interest to declare.