Postmenopausal women, men > age 50 years, or other patients with well-established causes of secondary osteoporosis (incl. glucocorticoid-induced osteoporosis, transplantation-related osteoporosis, disuse osteoporosis, etc.) N=20 treated with antiresorptive drugs N=10 treated with osteoanabolic drugs (e.g. teriparatide, Forsteo)

N=10 Patients with clinically obvious potential causes of calcium malabsorption (incl. severe vitamin D-deficiency, Scopinaro or other bariatric surgery, exocrine pancreatic insufficiency/steatorrhea, cystic fibrosis, inflammatory bowel disease, celiac disease, anorexia nervosa/eating disorders, malnutrition, etc.), with or without bone pains, muscle weakness and other typical osteomalacia symptoms. Confirmed by 24h urine collection showing calciuria <100 mg/24h.

Exploratory, heterogeneous group of calcium-related disorders (incl.hypercalcemia, hypocalcemia, primary/secondary/tertiary hyperparathyroidism, hypoparathyroidism, vitamin D deficiency, X-linked/autosomal dominant hypophosphatemic rickets, familial hypocalciuric hypocalcemia,etc.) N=20

N=40 Men and women ≤ 40 years recruited from the population

The sensitivity, specificity, positive and negative predictive value of the new test will be compared to expert clinical diagnosis as the gold standard. This diagnosis is established during follow-up and based on clinical observations, bone mineral density results/changes, bone turnover markers and response to treatments.

The sensitivity, specificity, positive and negative predictive value of the new test will be compared to expert clinical diagnosis as the gold standard. This diagnosis is established during follow-up and based on clinical observations, BMD results, bone turnover markers and response to treatments.