Sysmex XN-V scattergrams in feline mastocythemia and basophilia: Two similar but different cases

Scattergram evaluation is an important part of nonstatistical quality control in Veterinary Hematology. In this case report, we present two feline hematological cases with abnormal Sysmex XN-V scattergrams. Case 1 involved a 16-year-old neutered female domestic shorthair cat referred for the investigation of a suspected abdominal mass, which revealed marked mastocythemia on blood smear evaluation. Case 2 involved a 9-year-old castrated male domestic shorthair cat that was presented for follow-up after cystostomy and perineal urethrostomy, which revealed marked basophilia on blood smear evaluation. In both cases, an abnormal population was observed on the white cell differential channel by fluorescence (WDF) scattergram using a Sysmex XN-V hematology analyzer. The abnormal population appeared as an oval cloud of dots between monocytes and eosinophils. Manual re-gating of these unusual populations on the WDF channel correlates with manually determined counts. Mast cells appeared as a lysis-resistant population on the white count and nucleated red blood cell (WNR) scattergram, whereas basophils did not show this feature. Therefore, the appearance of an unexpected population between the eosinophil and monocyte area on the WDF scattergram may indicate mastocythemia or basophilia in cats. Further assessment of the WNR scattergram, focusing on identifying lysis-resistant populations, can help differentiate between basophilia and mastocythemia. However, blood smear evaluation remains mandatory for the accurate enumeration of basophils and/or determination of mastocythemia. Manufacturer software adjustments within the WDF and WNR channels may improve the accuracy of basophil counts in veterinary hematology.