ObjectiveTo investigate the clinical value of peripheral blood vitamin D level in predicting the outcome of weaning from mechanical ventilation in critically ill patients.MethodsA total of 130 critically ill patients who undergoing mechanical ventilation for more than 48 hours in our hospital were recruited from June 2014 to June 2017. Serum 25(OH)D3 was detected on admission and before spontaneous breathing test (SBT) meanwhile general clinical data and laboratory examination indexes were recorded. The cases were divided into a successful weaning group and a failure weaning group according to the outcome of weaning from mechanical ventilation. Logistic regression equation was used to analyze the relationship between vitamin D level and failure weaning, and a receiver operating characteristic (ROC) curve was used to analyze the predictive value for failure weaning.ResultsThere were 46 patients with failure weaning among 130 patients (35.38%). Compared with the successful weaning group, the failure weaning group had significantly higher Acute Physiology and Chronic Health EvaluationⅡ score, longer duration in intensive care unit, higher respiratory rate, higher rapid shallow breathing index, higher C-reactive protein, higher N-terminal prohormone of brain natriuretic peptide, higher serum creatinine, and significantly lower albumin (all P<0.05). 25(OH)D3 level classifications on admission and before SBT in the failure weaning group were worse than those in the successful weaning group (P<0.05). 25(OH)D3 levels of the failure weaning group were lower than those of the successful weaning group [on admission: (18.16±4.33) ng/ml vs. (21.60±5.25) ng/ml, P<0.05; before SBT: (13.50±3.52) ng/mlvs. (18.61±4.30) ng/ml, P<0.05]. Multivariate logistic regression analysis showed that 25(OH)D3 levels on admission and before SBT were independent risk factors for failure weaning (OR values were 2.257 and 2.613, respectively, both P<0.05). ROC curve analysis showed that areas under ROC curve were 0.772 and 0.836, respectively, with sensitivities of 80.3% and 85.2%, specificities of 69.0% and 71.0%, respectively.Conclusions25(OH)D3 deficiency or insufficiency is common in critically ill patients. The lower the level of vitamin D, the higher the risk of failure weaning. So it may be an independent predictor of failure weaning.