Platelet Aggregation Assays Do Not Reliably Diagnose Platelet Delta Granule Storage Pool Deficiency

Abstract

Background Patients with platelet dysfunction disorders present with a variety of mucocutaneous bleeding symptoms including easy bruising, frequent epistaxis, bleeding gums upon tooth brushing and for women, heavy menstrual bleeding. Available laboratory assays to evaluate platelet function include the platelet function analyzer (PFA) and in larger centers with coagulation laboratories, light transmission platelet aggregometry (LTA) analyses. Both assays are known to have a number of limitations, especially in the diagnosis of platelet delta granule storage pool deficiency (δ-SPD). δ-SPD is an underdiagnosed condition caused by decreased numbers of platelet dense granules (DGs) and is best diagnosed by electron microscopy (EM). Patients with platelet δ-SPD have a decreased response to low levels of the agonist adenosine diphosphate (ADP) in the second wave of light transmittance with LTA or decreased ADP secretion by fluorescence lumiaggregometry. There are few reports that have evaluated patients with δ-SPD and their respective LTA results. One report published in 1987 described normal LTA assays in 23% of patients with δ-SPD; a more recent report described LTA as having the sensitivity to detect only about 52% of patients with δ-SPD. The purpose of our study was intended to review the LTA and EM results of patients suspected of having a platelet function disorder at our institution for comparison with previously published studies. Methods Our study included 344 patients who had been evaluated by both LTA and whole mount EM. Aggregometry utilized five agonists: ADP, epinephrine, collagen, arachidonic acid, and ristocetin. DGs were enumerated in 100 whole-mounted platelets to determine a mean number of dense granules per platelet (DGs/PL). Results Seventy-seven percent of our patients were found to have δ-SPD (264/344); 68% (179/264) of these subjects had an abnormal platelet LTA. Thirty-two percent (85/264) of our patients had normal LTA results but were found to have δ-SPD with a mean of 2.54 ± 0.15 DG/PL (normal = 4 - 6 DG/PL). Conclusion These data confirm previous reports suggesting the utilization of LTA alone in patients with histories of unexplained bleeding may miss the diagnosis of platelet δ-SPD. It is, therefore, prudent to assess platelet DG number by EM, especially if platelet LTA assessment is normal.

Frequency, clinical, and laboratory findings of platelet secretion disorders in patients referred to the specialized coagulation laboratory of the Iranian Blood Transfusion Organization

“…with d-granule platelet storage pool deficiency by EM study had abnormal responses in LTA. Consistent with these findings, other studies also showed that 10 to 23% of patients with mild platelet disorders have normal LTA patterns [14,20]. The present study detected two patients with normal LTA pattern and abnormal ATP-releasing assay.…”

Platelet Delta (δ)-Storage Pool Deficiency: A Case Series and Review of the Literature

“…Eventually, platelets were evaluated with transmission electron microscopy (TEM) and demonstrated fewer dense granules, leading to the diagnosis of platelet δ-storage pool deficiency. In support, as LTA can show a false negative, it is reasonable to evaluate with TEM in patients with a BS > 6, given the exclusion of von Willebrand disease (vWD) [ 13 , 14 ]. Interestingly, Gresele et al demonstrated that a BS > 6 increased the likelihood of bleeding events in inherited platelet disorders and that a higher baseline BS was associated with more bleeding events, which can help determine the need for treatment [ 15 ].…”

Serotonin secretion by blood platelets: accuracy of high-performance liquid chromatography-electrochemical technique compared with the isotopic test and use in a clinical laboratory

“…PSDs are usually associated with abnormalities in light transmission aggregometry (LTA) but are also present in patients with normal platelet aggregation [ 2 , [4] , [5] , [6] ]. In this regard, a recent study found that LTA was normal in 32% of 264 patients with decreased number of δ-granules [ 7 ]. These observations support a recent guidance from the International Society on Thrombosis and Haemostasis Scientific Subcommittee (ISTH-SSC) SSC on Platelet Physiology to incorporate a δ-body secretion assay (PSA) in the first diagnostic stage of IPFD [ 8 ].…”