Association between vitamin D metabolites, vitamin D binding protein, and proteinuria in dogs

BACKGROUND: Proteinuria has been associated with progression of renal disease and increased morbidity and mortality in dogs and people. In people, proteinuria also has been associated with hypovitaminosis D. Little is known about the relationship between vitamin D metabolism and proteinuria in dogs. OBJECTIVES: To further elucidate vitamin D status in dogs with protein-losing nephropathy (PLN) and minimal to no azotemia. We hypothesized that vitamin D metabolites would be lower in dogs with PLN compared to healthy dogs. ANIMALS: Twenty-three client-owned adult dogs with PLN and 10 healthy control dogs. METHODS: Serum 25-hydroxyvitamin D (25[OH]D), 1,25-dihydroxyvitamin D (1,25[OH]₂ D), 24,25-dihydroxyvitamin D (24,25[OH]₂ D), serum vitamin D binding protein (VDBP), and urine 25(OH)D concentrations were measured. RESULTS: Compared to healthy dogs, dogs with PLN had lower concentrations of all vitamin D metabolites (P < .01). Correlations (rho; 95% confidence interval [CI]) in dogs with PLN are reported. Serum 25(OH)D and 24,25(OH)₂ D concentrations were positively correlated with albumin (r = 0.47; 0.07-0.74), and 24,25(OH)₂ D was negatively correlated with urine protein-to-creatinine ratio (UPC; r = -0.54; -0.78 to -0.16). Urine 25(OH)D-to-creatinine ratio was negatively correlated with serum albumin concentration (r = -0.77; -0.91 to -0.50) and positively correlated with UPC (r = 0.79; 0.53-0.91). Serum VDBP concentration was positively correlated with serum albumin concentration (r = 0.53; 0.05-0.81). CONCLUSIONS AND CLINICAL IMPORTANCE: Dogs with PLN have decreased serum concentrations of vitamin D metabolites. Urine 25(OH)D-to-creatinine ratio and UPC are correlated in PLN dogs. Future studies are needed to assess additional management strategies for dogs with PLN.