Classes of vitamin D status and functional outcome after hip fracture: a prospective, short-term study of 1350 inpatients.

BACKGROUND: Vitamin D depletion is associated with unfavourable outcomes after hip fracture. However, the classes of vitamin D status currently in use, which are defined according to serum calcifediol levels, have not been validated for their predictive capability of the functional recovery.

AIM: To investigate the association between serum calcifediol categorized into 4 classes and the functional recovery after hip fracture.

DESIGN: Prospective, short-term observational study.

SETTING: Rehabilitation hospital in Italy.

POPULATION: We evaluated 1350 of 1412 inpatients with hip fracture.

METHODS: Serum calcifediol was measured by an immunoenzymatic assay 14.7±4.4 (mean ± SD) days after surgery and categorized into 4 classes: I class <12ng/ml; II class 12-20ng/ml; III class 21-29ng/ml; IV class ≥30ng/ml. The functional outcome was assessed by using the Barthel index.

RESULTS: We found a significant difference in Barthel index scores at the end of inpatient rehabilitation across the 4 classes of vitamin D status: 2 (3, n=1350) 27.2; p<0.001. The difference persisted after adjustment for 8 covariates (p=0.004). By comparing pairs of classes, we found that Barthel index scores were lower in the 829 patients of the I class than in the 275 of the II (p=0.005) who had in turn Barthel index scores lower than the 132 patients of the III class (p=0.038). Conversely, no significant differences emerged between the patients of the III class and the 114 patients of the IV class (p=0.421). The results did not materially change when Barthel Index effectiveness was substituted for Barthel Index scores as the outcome measure.

CONCLUSIONS: Calcifediol levels below 12ng/ml were associated with a worse recovery than those between 12 and 20ng/ml that were in turn associated with a worse recovery than those between 21 and 29ng/ml. Conversely, no significant differences were found between the patients with calcifediol between 21 and 29ng/ml and those with calcifediol ≥30ng/ml.

CLINICAL REHABILITATION IMPACT: Despite caution due to the observational design, our study suggests that vitamin D depletion should be treated after hip fracture to optimize the functional outcome, with a target level for serum calcifediol of 21-29ng/ml and no further advantages associated with calcifediol levels of 30ng/ml or higher.