Diagnosis of inherited platelet disorders: comparison between immunofluorescence analysis on the blood smear and genetic testing

Objective Inherited platelet disorders (IPD) are rare diseases featured by reduced platelet count and/or impaired platelet function. Diagnostic tools include clinical evaluation, platelet function tests and genetic analysis. We have established a method to assess platelet phenotype on the blood smear by immunofluorescence microscopy as a diagnostic tool for IPDs. The aim of the study was to compare the outcomes of the immune-morphological analysis with those of genetic testing in a cohort of consecutive patients suspected for IPD.

Material and Methods Three reference Institutes for the diagnosis of IPD from Greifswald, Germany, Murcia, Spain, and Copenhagen, Denmark, participated in the study. The subjects were enrolled from January 2019 to September 2020 by Centers of Copenhagen and Murcia, to whom they had been referred for genetic investigation. The blood smears were centralized in the Greifswald Center, where the immune-morphological assessment was blindly performed. The morphologic changes were reported and the potential diagnoses were formulated. Subsequently, the genetic results were unblinded and the comparison performed. Patients signed written informed consent.

Results 75 consecutive subjects belonging to 56 unrelated pedigrees were enrolled. The microscopic analysis identified alterations suggestive for a form of IPD in 38 cases (51 %). In 33 (44 %), abnormalities not typical for known IPD were reported. In 4 (5 %), no morphologic alterations were found. The genetic testing diagnosed a specific IPD in 54 cases (72 %). In 15 (20 %) and 6 (8 %) variants of uncertain significance (VUS) and no variants were found, respectively. Among 19 forms of IPD with a confirmed genetic mutation, in 11 immunofluorescence correctly predicted the affected gene by the typical morphologic pattern. In further 3 disorders, unreported characteristic morphologic patterns were identified, while in 5 disorders, immunofluorescence showed unclear findings. Among 21 patients without genetic diagnosis, in 20 immunofluorescence found morphologic alterations in platelet structures, which could explain platelet dysfunction.

Conclusion Immunofluorescence analysis on the blood smear is an effective diagnostic tool for a substantial group of IPD. It can guide geneticist to interpret VUS and provide clinicians with relevant information about changes in platelet structure, which can explain the bleeding phenotype of patients.

Publication History

Article published online:
18 June 2021