Diagnosing Inherited Platelet Disorders: Immunofluorescence on the Blood Smear in Comparison With Genetic Testing

Carlo Zaninetti, M.D., Ph.D.
University Medicine Greifswald
Greifswald, Germany

On Sunday, July 19, 2021, Carlo Zaninetti of the Institut für Immunologie und Transfusionsmedizin, Universitätsmedizin Greifswald in Germany, presented results on the comparison between immunofluorescence and genetic testing for diagnosing inherited platelet disorders (IPDs). IPDs are rare diseases featured by low platelet count and/or defective platelet function. Patients have variable bleeding diathesis and sometimes additional clinical features that can be congenital or acquired. Identification of an IPD is challenging but desirable to avoid the misdiagnosis of immune thrombocytopenia and the use of improper treatments. Zaninetti commented that via immunofluorescence microscopy, they had established a screening tool for IPD on the blood smear. The aim of the presented study was to see how the outcomes of immunofluorescence in a cohort of patients with suspected IPDs would compare with the molecular ones. Of the 94 enrolled subjects, microscopic analysis identified alterations suggestive of a specific IPD in 50 cases. In 39, abnormalities not typical for known IPDs were reported, and in five, no alterations were found. Genetic testing diagnosed a specific IPD in 42 pedigrees. In total, 20 different IPDs were identified. Among these, 11 were identified by immunofluorescence based on known specific phenotypic changes. In two forms, previously unreported phenotypes were described, while in the other forms immunofluorescence found unclear or unspecific patterns. Zaninetti concluded that (i) immunofluorescence on the blood smear is an effective diagnostic tool for a substantial group of IPDs, (ii) it can help variant of uncertain significance (VUS) interpretation, and (iii) it provides clinicians with relevant information about changes in platelet structures that may account for the bleeding phenotype of the patients.

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