RAPID DETECTION OF HEREDITARY AND ACQUIRED PLATELET STORAGE POOL DEFICIENCY BY FLOW-CYTOMETRY

Platelet aggregation is commonly used to investigate patients with pos sible dense granule storage pool deficiency (delta SPD), but recent st udies have shown that this investigation is not specific or sensitive for this disorder. We describe a simple one-step technique to detect m epacrine loaded platelets by flow cytometry and found a good correlati on (r = 0.83) between this method and the enumeration of platelet dens e granules by conventional fluorescent microscopy. Seven patients with congenital delta SPD had significantly (P < 0.001) reduced mepacrine labelling detected by flow cytometry (mean 15%; range 5-23%) compared to normal controls (mean 48%; normal range 32-64%). Six patients with other hereditary platelet disorders had normal mepacrine labelling (me an 49%; range 34-66%) and were clearly distinguished from patients wit h delta SPD despite similar platelet aggregation patterns. Acquired de lta SPD is frequently associated with the platelet function defect des cribed in the myeloproliferative and myelodysplastic disorders (MPD/MD S) and we compared platelet aggregation and mepacrine labelling in 15 of these patients. The results confirm that delta SPD occurs commonly in MPD/MDS with 7/15 patients having reduced mepacrine staining but, l ike the findings in hereditary delta SPD, 3/7 patients with normal pla telet aggregation had delta SPD. Similarly abnormal platelet aggregati on was not diagnostic of delta SPD as 4/8 of these patients had normal mepacrine levels. These results may contribute to the known lack of c orrelation between the limited assessment of platelet function and ble eding events in MPD/MDS. We found mepacrine labelling of platelets det ected by flow cytometry to be a useful, simple and inexpensive method to detect hereditary and acquired delta SPD which will improve the def inition of the platelet defect in these disorders in the clinical labo ratory.