A reliable digital photomicroscopic method of nailfold plexus visibility assessment in schizophrenia

High nailfold plexus visibility (NPV) is a trait identifying a putative endophenotype for schizophrenia. We describe a new method of NPV assessment using computer storage of digital photomicrographs. We performed a reliability study of this method using 40 subjects. The intraclass correlation between two blinded raters was 0.83. The kappa coefficient for a 3 level division of NPV was 0.72, while the kappa for reliability at the cutting score for designating high NPV was 0.94. This method provides immediate image quality feedback, ease of reliability assessment, the option of blinded ratings, and a method for continuous enhancement of rating consensus.