IONIZED HYPOCALCEMIA AND URINARY CALCIUM DURING SIRS IN DOGS: INCIDENCE AND PROGNOSTIC SIGNIFICANCE

Introduction/Objectives: Ionized Hypocalcemia (iHCa) is a common electrolyte disturbance in critically ill patients of potentially prognostic significance. The pathogenesis of iHCa is likely multifactorial, including an increase in urinary fractional excretion of calcium (FECa). The aim of this preliminary study was to determine the incidence and the prognostic significance of iHCa during the Systemic Inflammatory Response Syndrome (SIRS) in dogs. Furthermore a potential correlation between low Ionized Calcium (iCa) concentration and FECa was investigated in this population. Methods: Dogs admitted to the University of Bologna Veterinary Teaching Hospital between December 2010 and July 2011 with clinical signs of SIRS (T< 38°C or > 39°C; HR > 120/min; RR > 20/min, WBC count > 16000 or < 6000 cells/μL) were selected. Cases were excluded if younger than 1 year of age, diagnosed with Chronic Kidney Disease or parathyroid glands diseases, or recently treated with drugs known to alter iCa concentration. Venous blood gas analysis, including iCa measurement, and urinalysis with FECa calculation were performed upon admission. Additional laboratory analysis included measurement of C-Reactive Protein (CRP), lactate, Antithrombin Activity (AT), proteinuria and albuminuria. Illness severity was calculated by the Acute Patient Physiologic and Laboratory Evaluation (APPLE) Fast Score. A group of healthy dogs (n=32) was included as negative control. Non parametric statistics (Mann Whitney U-Test and Spearman's Correlation Coefficient) and regression analysis were performed. Statistical significance was set at p<0,05. Results: 22 dogs with SIRS were enrolled. The incidence of iHCa (iCa < 1,21 mmol/L) was 31,8% (median=1,22; 1,07-1,36). iHCa was not associated with outcome or duration of hospital stay. FECa (%) was significantly higher in SIRS (median=0,23; 0,06-1,61) compared to healthy dogs (median=0,10; 0,03-0,68), but mostly within the reference interval. No correlation between FECa and iHCa was found. Lactate, BE, Urine Protein/Creatinine Ratio (UPC), Urine Albumin/ Creatinine Ratio (UAC) and the APPLE Fast Score were all significantly increased in non-survivors compared to survivors. After multivariate analysis was performed, AT and APPLE Fast Score were the only variable significantly associated with outcome (p <0,004 and 0,003 respectively) Discussion: The incidence of iHCa in this population is higher than previously reported in critically ill dogs, and no association with prognosis was identified. Renal loss of calcium does not seem to be the major cause of iHCa in dogs with SIRS. However, other pathogenetic mechanisms of iHCa during critical illness have not been inestigated. AT and APPLE Fast Score show a significant prognostic value in this population. Conclusion: Ionized Hypocalcemia is confirmed in dogs with SIRS; its potential prognostic significance during the course of this syndrome needs to be clarified in a larger population. Increased urine calcium does not seem to be associated with iHCa in critically ill dogs. Further prospective studies investigating other potential causes of iHCa, including a disruption in the parathyroid- vitamin D axis and increment in circulating inflammatory cytokines and calcitonin precursors, are needed.