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High diagnostic accuracy of the sysmex XT 2000iv delta WBC on effusions for feline infectious peritonitis
Journal article   Peer reviewed

High diagnostic accuracy of the sysmex XT 2000iv delta WBC on effusions for feline infectious peritonitis

A. Giordano, G. Rossi and S. Paltrinieri
Veterinary Clinical Pathology, Vol.42(4), E27
2013
DOI: https://doi.org/10.1111/vcp.12091
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Abstract

Delta WBC (DWBC, ratio between the cell counts in the DIFF and BASO channel of the laser counter Sysmex XT2000iV) has been reported to be high in cats with feline infectious peritonitis (FIP). The aim of this study was to assess the diagnostic accuracy of the DWBC for FIP and to define the best cutoff value to diagnose FIP. From 56 effusions, 25 were from cats with FIP, and 31 from cats with other diseases (19 tumors; 8 inflammation; 4 cardiogen), diagnosed by cytology, necropsy or serum protein electrophoresis and a1-acid glycoprotein, analyzed within 12 hours from collection. WBC differential (DIFF) and basophil (BASO) counts and DWBC were recorded. Results of the 2 groups were statistically compared and sensitivity, specificity and positive likelihood ratio (LR+) were calculated. A ROC curve was designed and the ideal cut-off value determined. The DWBC was significantly higher (P < .001) in FIP (mean _ SD: 12.5 _ 11.2; median: 8.16; min-max: 0.5-36.4) than in non-FIP cats (1.1 _ 0.4; 1.0; 0.5-2.5). The BASO and DIFF counts (cells x 103/lL) were significantly lower (P < .001 and P < .05) in FIP cats (BASO = 0.5 _ 1.1; 0.2; 0.0-5.3; DIFF = 4.5 _ 7.4; 1.3; 0.1-26.3) than in non-FIP cats (BASO = 43.5 _ 127.0; 10.1; 0.0-707.9 DIFF = 52.6 _ 164.6; 9.1; 0.1-34.6). All FIP cats had a DWBC > 3.0, except 2 cats, which had “atypical” FIP (one with a severe hepatic failure and one with a pericardial effusion). All non-FIP cats had a DWBC < 3.0. The area under the ROC curve was 0.95 (P < .001). The best cut-off was 1.7 (Sens: 92%; Spec: 93.5%; LR+: 14.3). The specificity increased to 100% using a cut-off of 2.5. This study confirms the high diagnostic accuracy of the DWBC for FIP. This is due to clot formation in the BASO reagent, resulting in cell entrapment, similar to the Rivalta test reaction that has a high diagnostic accuracy for FIP.

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