Diagnostic accuracy of flow cytometric perforin screening. (A) Diagnostic accuracy of perforin flow cytometric screening to detect patients with biallelic pathological PRF1 mutations compared with patients with normal sequencing results, using the laboratory-determined normal range for perforin mean channel fluorescence (MCF) in NK cells. (B) Violin plot representation of NK-cell perforin MCF in relation to genetic classification including affected (biallelic disease-causing mutations), carrier (monoallelic mutation with or without additional variants of uncertain clinical significance), variant(s) of unknown clinical significance (VUCS), A91V variant(s), and normal. The laboratory normal control range threshold (perforin MCF, 98) is shown with a dashed line, and the optimum diagnostic threshold obtained by an analysis of receiver operating characteristics (perforin MCF <49) is shown with a dashed line. (C) Receiver operating characteristic curve analysis of perforin MCF showing optimal threshold test characteristic as determined by the Youden index (*). Area under the curve is 0.974. (D) Diagnostic accuracy of perforin flow cytometric screening to detect patients with biallelic pathological PRF1 mutations compared with patients with normal sequencing results, monoallelic mutation with or without additional variants of uncertain clinical significance, and VUCS using the optimal diagnostic threshold established by receiver operating characteristic curve analysis.