Development of a Clinical Risk Score for the Identification of Hypovitaminosis D

Background/Objectives: Hypovitaminosis-D is a highly prevalent condition worldwide, associated with adverse skeletal and extra-skeletal outcomes. Increasing demand for serum 25-hydroxyvitamin D (25(OH)D) testing points toward the need for simple tools to identify individuals at risk and optimize laboratory use. We aimed to develop and validate a clinical risk score for predicting hypovitaminosis-D based on easily assessable risk factors. Methods: This cross-sectional study included 1,408 adults across Italy. Demographic, clinical, lifestyle, and dietary data were collected through a standardized questionnaire. Univariable and multivariable logistic regression analyses identified predictors of 25(OH)D <20 ng/mL and <30 ng/mL. Risk scores were derived from models. Discriminative ability was assessed using ROC curves, and calibration by comparing predicted and observed probabilities. Results: Median age was 67 years, and 91.3% were female. Median 25(OH)D was 33.2 ng/mL; 9.8% had levels <20 ng/mL. Independent predictors of hypovitaminosis-D (25(OH)D <20 ng/mL) included higher body mass index, residence in Northern Italy, reduced summer sun exposure, sunscreen use, cardiovascular disease, glucocorticoid use, absence of cholecalciferol supplementation, and no prior vitamin D use. The score (range 9-18) showed good discrimination (Area under the curve; AUC: 79.1%, 95% CI 75.3-82.9) and excellent calibration (r=0.98, p<0.001). A screening cut-off (10.3-10.7) ensured high sensitivity (87.0-92.7%), while 11.9-12.0 balanced sensitivity (~62%) and specificity (~80%). A second score for 25(OH)D <30 ng/mL showed moderate discrimination (AUC: 69.6%). Performance remained stable across seasons and in untreated subjects (AUC: 72.7%). Conclusions: A simple, data-driven clinical risk score identifies individuals at risk of hypovitaminosis-D and may support targeted screening, reduce unnecessary testing, and improve cost-effectiveness in clinical practice.