Dysregulated mineral metabolism in patients with acute kidney injury and risk of adverse outcomes

OBJECTIVE: Numerous studies have evaluated the prevalence and importance of vitamin D deficiency among patients with chronic kidney disease and end-stage renal disease; however, little is known about vitamin D levels in acute kidney injury (AKI). We evaluated the association between vitamin D metabolites and clinical outcomes among patients with AKI. DESIGN: Prospective cohort study. PATIENTS: A total of 30 participants with AKI and 30 controls from general hospital wards and intensive care units at a tertiary care hospital were recruited for the study. MEASUREMENTS: Plasma levels of 25-hydroxyvitamin D 25(OH)D, 1,25-dihydroxyvitamin D 1,25(OH)2 D, 24R,25-dihydroxyvitamin D3 , vitamin D binding protein (VDBP) and fibroblast growth factor 23 (FGF23) were measured within 24 hours of AKI onset and 5 days later. Bioavailable 25(OH)D and 1,25(OH)2 D levels, defined as the sum of free- and albumin-bound 25(OH)D and 1,25(OH)2 D, were estimated using equations. RESULTS: Compared to controls, participants with AKI had lower levels of 1,25(OH)2 D 17 (10-22) vs 25 (15-35) pg/ml, P = 0·01, lower levels of VDBP 23 (15-31) vs 29 (25-36) mg/dl, P = 0·003 and similar levels of bioavailable 25(OH)D and 1,25(OH)2 D at enrolment. Levels of bioavailable 25(OH)D were inversely associated with severity of sepsis in the overall sample (P < 0·001). Among participants with AKI, bioavailable 25(OH)D, but not other vitamin D metabolites, was significantly associated with mortality after adjusting for age and serum creatinine (adjusted odds ratio per 1 SD ln bioavailable 25(OH)D = 0·16, 95% confidence interval = 0·03-0·85). CONCLUSIONS: Bioavailable 25(OH)D could have a role as a biomarker or mediator of adverse outcomes among patients with established AKI.