A new index for distinguishing hypereosinophilic syndrome and antineutrophil cytoplasmic antibody-negative eosinophilic granulomatosis with polyangiitis

Background: It is difficult to differentiate between hypereosinophilic syndrome (HES) and antineutrophil cytoplasmic antibody (ANCA)-negative eosinophilic granulomatosis with polyangiitis (EGPA).Objective: We compared laboratory data at diagnosis between Korean patients with HES and ANCA-negative EGPA and investigated independent laboratory predictors suggesting HES.Methods: We reviewed the medical records of 41 HES patients and 16 ANCA-negative EGPA patients. The cut-offs were extrapolated by the receiver operator characteristic (ROC) curve. The odds ratio (OR) and relative risk (RR) were assessed using the multivariable logistic regression analysis and the chi-square test, respectively. We developed a new equation by assigning a weight to each variable according to the slopes (B) and expressed a decimal as the nearest integer.Results: HES patients had a higher median WBC and eosinophil counts than ANCA-negative EGPA patients. The cutoffs of WBC and eosinophil counts for HES were set at 9,900.0/mm(3) and 2,400.0/mm(3). In the multivariable analysis, WBC count >= 9,900.0/mm(3) (B 1.763) and eosinophil count >= 2,400.0/mm(3) (B 1.515) were significantly associated with HES. An equation was as follows: HES-suggesting laboratory index (HSLI) = 2 x (WBC count >= 9,900.0/mm(3) (1 = No or 2 = Yes)) + 1.5 x (eosinophil count >= 2,400.0/mm(3) (1 = No or 2 = Yes)). The cut-off of HSLI for HES was 4.25. Patients with HSLI >= 4.25 exhibited a significantly high RR (51.429) for HES, compared to those without.Conclusions: In conclusion, the cut-off of HSLI derived from WBC and eosinophil counts could be an independent predictor of HES in patients suspected of both HES and ANCA-negative EGPA.