Age-dependent changes in plasma concentrations of 25-hydroxyvitamin D may complicate vitamin D status assessment of immature cats

Vitamin D deficiency and excess in clinically presented cats conventionally is diagnosed by comparison of patient plasma 25-hydroxyvitamin D (25 (OH)D) concentration with plasma reference intervals determined in healthy adult cats. For immature cats, validity of this vitamin D status assessment method is uncertain. The overall objective was determination of whether plasma concentration of 25 (OH) D and other vitamin D metabolites in immature cats markedly change with developmental age as has been reported in other species. Four male and 4 female domestic short-hair kittens from weaning were continuously presented a single nutritionally adequate growth-diet. Concentrations of 25 (OH) D and 24,25-dihydroxyvitamin D (24,25 (OH) D), and calcitriol were quantified in plasma of jugular venous blood collected at 12, 15, 18, and 21 weeks and 1 year of age. Plasma was liquid and solid-phase extracted and fractionation by normal-phase HPLC, and 25 (OH) D and 24,25 OH) D quantified by reverse-phase HPLC-UV and calcitriol by RIA. Plasma 3-epi-25 (OH) D and 25 (OH) D concentrations increased (