Flow cytometric mepacrine fluorescence can be used for the exclusion of platelet dense granule deficiency

Background: δ-storage pool disease (δ-SPD) is a bleeding disorder characterized by a reduced number of platelet-dense granules. The diagnosis of δ-SPD depends on the measurement of platelet ADP content, but this test is time consuming and requires a relatively large blood volume. Flow cytometric analysis of platelet mepacrine uptake is a potential alternative, but this approach lacks validation, which precludes its use in a diagnostic setting. Objectives: To evaluate the performance of platelet mepacrine uptake as a diagnostic test for δ-SPD. Patients/Methods: Mepacrine fluorescence was determined with flow cytometry before and after platelet activation in 156 patients with a suspected platelet function disorder and compared with platelet ADP content as a reference test. Performance was analyzed with a receiver operating characteristic (ROC) curve. Results: Eleven of 156 patients had δ-SPD based on platelet ADP content. Mepacrine fluorescence was inferior to platelet ADP content in identifying patients with δ-SPD, but both mepacrine uptake (area under the ROC curve [AUC] 0.87) and mepacrine release after platelet activation (AUC 0.80) had good discriminative ability. In our tertiary reference center, mepacrine uptake showed high negative predicitive value (97%) with low positive predictive value (35%). Combined with a negative likelihood ratio of 0.1, these data indicate that mepacrine uptake can be used to exclude δ-SPD in patients with a bleeding tendency. Conclusion: Mepacrine fluorescence can be used as a screening tool to exclude δ-SPD in a large number of patients with a suspected platelet function disorder.