High diagnostic accuracy of the Sysmex XT-2000iV delta total nucleated cells on effusions for feline infectious peritonitis

Background: The \u394WBC (the ratio between DIFF and BASO counts of the Sysmex XT-2000iV), hereafter defined as \u394TNC (total nucleated cells), is high in effusions due to feline infectious peritonitis (FIP), as cells are entrapped in fibrin clots formed in the BASO reagent. Similar clots form in the Rivalta's test, a method with high diagnostic accuracy for FIP. Objectives: The objective of this study was to determine the diagnostic accuracy for FIP and the optimal cutoff of \u394TNC. Methods: After a retrospective search of our database, DIFF and BASO counts, and the \u394TNC from cats with and without FIP were compared to each other. Sensitivity, specificity, and positive and negative likelihood ratios (LR+, LR-) were calculated. A ROC curve was designed to determine the cutoff for best sensitivity and specificity. Results: Effusions from 20 FIP and 31 non-FIP cats were analyzed. The \u394TNC was higher (P 2.5 had 100% specificity. Conclusions: The \u394TNC has a high diagnostic accuracy for FIP-related effusions by providing an estimate of precipitable proteins, as the Rivalta's test, in addition to the cell count. As fibrin clots result in false lower BASO counts, the \u394TNC is preferable to the WBC count generated by the BASO channel alone in suspected FIP effusions