Prevalence of subclinical contributors to low bone mineral density and/or fragility fracture.

OBJECTIVE The prevalence of subclinical contributors to low bone mineral density (BMD) and/or fragility fracture is debated. We evaluated the prevalence of subclinical contributors to low BMD and/or fragility fracture in the presence of normal 25-hydroxyvitamin D (25OHVitD) levels. DESIGN Prospective observational study. METHODS Among 1095 consecutive outpatients evaluated for low BMD and/or fragility fractures, 602 (563 females, age 65.4±10.0 years) with apparent primary osteoporosis were enrolled. A general chemistry profile, phosphate, 25OHVitD, cortisol after 1-mg overnight dexamethasone suppression test, antitissue transglutaminase and endomysial antibodies and testosterone (in males) were performed. Serum and urinary calcium and parathyroid hormone levels were also evaluated after 25OHVitD levels normalization. Vertebral deformities were assessed by radiograph. RESULTS In total, 70.8% of patients had low 25OHVitD levels. Additional subclinical contributors to low BMD and/or fragility fracture were diagnosed in 45% of patients, with idiopathic hypercalciuria (IH, 34.1%) and primary hyperparathyroidism (PHPT, 4.5%) being the most frequent contributors, apart from hypovitaminosis D. Furthermore, 33.2% of IH and 18.5% of PHPT patients were diagnosed only after 25OHVitD levels normalization. The subclinical contributors to low BMD and/or fragility fracture besides hypovitaminosis D were associated inversely with age (odds ratio (OR) 1.02, 95% CI 1-1.04, P=0.04) and BMI (OR 1.1, 95% CI 1.05-1.17, P=0.0001) and directly with fragility fractures (OR 1.89, 95% CI 1.31-2.73, P=0.001), regardless of BMD. CONCLUSIONS Subclinical contributors to low BMD and/or fragility fracture besides hypovitaminosis D are present in more than 40% of the subjects with apparent primary osteoporosis. Hypovitaminosis D masks a substantial proportion of IH and PHPT patients.