Diagnostic laboratory standardization and validation of platelet transmission electron microscopy.

Platelet transmission electron microscopy (PTEM) is considered the gold standard test for assessing distinct ultrastructural abnormalities in inherited platelet disorders (IPDs). Nevertheless, PTEM remains mainly a research tool due to the lack of standardized procedures, a validated dense granule (DG) count reference range, and standardized image interpretation criteria. The aim of this study was to standardize and validate PTEM as a clinical laboratory test. Based on previously established methods, we optimized and standardized preanalytical, analytical, and postanalytical procedures for both whole mount (WM) and thin section (TS) PTEM. Mean number of DG/platelet (plt), percentage of plts without DG, platelet count (PC), mean platelet volume (MPV), immature platelet fraction (IPF), and plt light transmission aggregometry analyses were measured on blood samples from 113 healthy donors. Quantile regression was used to estimate the reference range for DG/plt, and linear regression was used to assess the association of DG/plt with other plt measurements. All PTEM procedures were standardized using commercially available materials and reagents. DG interpretation criteria were established based on previous publications and expert consensus, and resulted in improved operator agreement. Mean DG/plt was stable for 2 days after blood sample collection. The median within patient coefficient of variation for mean DG/plt was 22.2%; the mean DG/plt reference range (mid-95th %) was 1.2-4.0. Mean DG/plt was associated with IPF (p = .01, R2 = 0.06) but not age, sex, PC, MPV, or plt maximum aggregation or primary slope of aggregation (p > .17, R2 < 0.02). Baseline ultrastructural features were established for TS-PTEM. PTEM was validated using samples from patients with previously established diagnoses of IPDs. Standardization and validation of PTEM procedures and interpretation, and establishment of the normal mean DG/plt reference range and PTEM baseline ultrastructural features, will facilitate implementation of PTEM as a valid clinical laboratory test for evaluating ultrastructural abnormalities in IPDs.

Comprehensive Platelet Phenotypic Laboratory Testing and Bleeding History Scoring for Diagnosis of Suspected Hereditary Platelet Disorders: A Single-Institution Experience.

OBJECTIVES: Patients with hereditary/congenital platelet disorders (HPDs) have a broad range of clinical manifestations and laboratory phenotypes. We assessed the performance characteristics of the International Society on Thrombosis and Haemostasis bleeding assessment tool (ISTH-BAT) and clinically validated platelet laboratory tests for diagnosis of HPDs. METHODS: The records of 61 patients with suspected HPDs were reviewed and ISTH-BAT scores calculated. RESULTS: Nineteen (31%) patients had thrombocytopenia, and 46 (75%) had positive ISTH-BAT scores. Thirteen and 17 patients had prolonged PFA-100 (Dade Behring, Miami, FL) adenosine diphosphate and epinephrine closure times, respectively. Twenty-two had abnormal platelet light transmission aggregation. Twenty-four had platelet transmission electron microscopy (PTEM) abnormalities (10 dense granule deficiency, 14 other ultrastructural abnormalities). Positive ISTH-BAT scores were associated with thrombocytopenia (P < .0001) and abnormal PTEM (P = .002). Twenty-three patients had normal results. CONCLUSIONS: ISTH-BAT identified patients with suspected HPDs but lacked a robust association with laboratory abnormalities. Despite comprehensive laboratory testing, some patients may have normal results.