Background: Inherited platelet disorders (IPDs) are rare diseases featured by thrombocytopenia and/or impaired platelet function. IPD diagnosis is challenging. The immune-morphological analysis of blood smears (by light- and immunofluorescence microscopy) is an effective and time-efficient tool to guide IPD diagnostic work-up. It requires low blood volume (< 100 µL) and is applicable to shipped samples.

Aims: To report the one-year experience in diagnosing IPDs on blood smear at the reference laboratory of University Medicine Greifswald, Germany.

Methods: We systematically assessed outcomes of blood smear analyses referred for suspected IPD under clinical routine conditions from January to December 2019 (all study patients were excluded). For immunofluorescence assessment, a panel of 13 antibodies against specific platelet structures has been applied. The study complies with the Declaration of Helsinki.

Results: Out of 345 referred patients (female 62%, mean age of 27; 32% children), in 125 (36%) the blood smear assessment showed normal findings. 124 (36%) had low platelet counts and 76 (22%) overt alteration of platelet morphology (mainly platelet macrocytosis). Immune-morphological analysis of blood smears provided a definitive diagnosis in 139 (40%): alpha- and/or delta storage-pool deficiencies (n=70, 50%); TUBB1-related thrombocytopenia (n=16); biallelic-and monoallelic Bernard-Soulier syndrome (n=7 and 8); MYH9-related thrombocytopenia (n=12); classic- and dominant Glanzmann thrombasthenia (n=1 and 10); FLNA-related thrombocytopenia (n=6); GFI1B-related thrombocytopenia (n=4); Wiskott-Aldrich syndrome (n=4); GATA1-related thrombocytopenia (n=1). In 81 (24%) patients no specific diagnosis was possible, despite alteration of one or more platelet structures, among them alterations of cytoskeletal markers were found in 52 patients (64%) (e.g. alpha-, beta-1 tubulin or filamin A). The possible pathogenic role of such cytoskeletal defects currently represents a major research question.

Conclusions: Immune-morphological analysis of blood smears is a valid diagnostic tool for IPDs. The method is able to identify a subset of patients probably worth of further investigations both for clinical and research purposes.

[Outcomes of one-year experience in diagnosing IPDs on a blood smear at our Institute]

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ISTH Congress Abstracts - https://abstracts.isth.org/abstract/diagnosis-of-inherited-platelet-disorders-on-a-of-blood-smear-the-one-year-experience-a-reference-laboratory/