Significant perturbation of vitamin D–parathyroid–calcium axis and adverse clinical outcomes in critically ill patients

A prospective multicentre cohort study was conducted to determine the prevalence of hypovitaminosis D in adult critically ill patients, to characterize alterations in the parathyroid hormone (PTH)–vitamin D–calcium axis and to explore associations between hypovitaminosis D and adverse clinical outcomes.

Demographic, disease severity scores and clinical outcome data were collected in 100 consecutive patients with expected intensive care unit (ICU) admission of at least 2 days. Levels of 25-hydroxyvitamin D (25-OH-D), 1,25-dihydroxyvitamin D (1,25-(OH)₂-D), PTH and ionized calcium were measured on days 1, 3 and on day 7 or ICU discharge.

The prevalence of vitamin D insufficiency (25 nmol/L ≤ 25-OH-D ≤ 50 nmol/L) and deficiency (25-OH-D < 25 nmol/L) were 54 and 24 %, respectively, and levels did not recover during ICU stay. Admission 25-OH-D levels correlated with 1,25-(OH)₂-D (R = 0.61, p = 0.001), Simplified Acute Physiology Score (SAPS-II) (R = −0.3, p = 0.01), Acute Physiology and Chronic Health Evaluation (APACHE-II) scores (R = −0.2, p = 0.05), but not calcium (R = 0.16, p = 0.11) or PTH (R = −0.11, p = 0.31) levels. Vitamin D deficiency was associated with fewer hospital-free days, OR 3.15 (1.18–8.43) in univariate analysis. Secondary hyperparathyroidism (PTH > 7 pmol/L) was observed in 37.5 % of hypocalcaemic and 32.5 % of vitamin D insufficient/deficient patients, and was associated with higher SAPS-II [43 (31.3–60) vs. 36 (30–43), p = 0.03].

Hypovitaminosis D and secondary hyperparathyroidism are highly prevalent in critically ill patients. Low vitamin D status persists during ICU stay and is associated with worse disease severity and fewer hospital-free days.