Nucleated red blood cells for characterization of systemic inflammatory response syndrome in dogs

Background: Nucleated red blood cells (nRBCs) are increased by disease processes and hematopoietic stress. Objectives: To evaluate the utility of nRBCs as a marker of disease severity and prognosis in dogs with systemic inflammatory response syndrome (SIRS). Animals: Sixty-two client-owned dogs met the criteria of SIRS without anemia. Methods: nRBC-positive (nRBCs: ≥5/500, n = 32) and nRBC-negative (nRBCs: <5/500, n = 30) dogs were classified, and clinicopathological data, Acute Patient Physiologic and Laboratory Evaluation (APPLE_fast) scores, cytokines, 2- and 4-weeks survival were compared. Results: The median WBC (17.63, interquartile range [IQR]: 11.72-20.24 × 10⁹/L), neutrophils (12.28, IQR: 7.17-16.88 × 10⁹/L), band neutrophils (1288.5, IQR: 252.5-2575 cells/μL), serum IL-6 (731.80, IQR: 299.79-5522.05 pg/mL), and plasma C-reactive protein (4.10, IQR: 1.00-8.58 mg/L) were significantly higher in nRBC-positive dogs than negative dogs (11.27, IQR: 7.63-15.13 × 10⁹/L; 7.57, IQR: 4.96-11.71 × 10⁹/L; 62.5, IQR: 0-350.25 cells/μL; 232.30, IQR: 99.33-447.01 pg/mL; 0.40, IQR: 0.10-3.00 mg/L, respectively; P <.05). The median reticulocyte count (87.95, IQR: 52.45-130.55 × 10³/μL) and serum IL-3 (40.94, IQR: 29.85-53.52 ng/L) were also significantly greater in nRBC-positive dogs than nRBC-negative dogs (46.00, IQR: 26.43-68.15 × 10³/μL; 25.24, IQR: 21.65-37.40 ng/L, respectively; P <.01). The presence of circulating nRBCs, but not the reticulocyte count, at admission was predictive of death in dogs with SIRS at 2 weeks (P =.01, AUC: 0.729) and 4 weeks (P =.002, AUC: 0.731). The overall survival time was shorter in nRBC-positive dogs (95% CI, 47.35-113.90) than nRBC-negative dogs (95% CI, 90.92-135.55; P =.03). Conclusions and Clinical Importance: Measuring peripheral nRBCs in dogs with SIRS is rapid and clinically applicable, reflecting disease severity and associated prognosis.