Comparison of EBER flow FISH results from two facilities

Epstein-Barr virus (EBV) primarily infects B cells but can occasionally target T and/or NK cells, leading to chronic active EBV disease or EBV-associated hemophagocytic lymphohistiocytosis, which are often difficult to treat. EBV-associated diseases exhibit a wide range of phenotypes. EBV-infected cells play a major role in pathogenesis, making their identification essential for diagnosis. EBV-encoded small RNA (EBER) flow fluorescence in situ hybridization (FISH), combined with multicolor flow cytometry, allows highly sensitive detection of EBV-infected cells, even from limited samples. However, EBER flow FISH is labor-intensive and requires technical expertise, limiting its use in standard facilities. We investigated whether the technique used in our department could be successfully implemented in other facilities. We performed EBER flow FISH at our department (Facility A) on cryopreserved peripheral blood mononuclear cell samples from seven patients diagnosed with EBV-associated diseases. The same assay was then conducted at Facility B, and results were compared for cell populations and the frequency of EBER-positive cells within each population. Significant correlations were observed between facilities for both cell fraction proportions and the proportion of EBER-positive cells. Among data points where both facilities detected ≥5% EBER-positive cells, 6 of 8 data points (75%) were within the acceptance interval of ±20%. Although one patient with very low proportions of EBER-positive cells showed inconsistent findings, overall results did not differ significantly between facilities. Although further validation in larger multicenter studies is required, these findings suggest preliminary interlaboratory comparability and support the potential transferability of EBER flow FISH across institutions.