Secondary causes of osteoporosis tests

Secondary Causes of Osteoporosis: Tests to Order and When to Refer recommends a staged diagnostic pathway: evaluate any patient with osteoporosis (defined by WHO as a DXA T-score ≤ −2.5 or any low-trauma fragility fracture) for secondary causes using targeted first-line tests and reserve specialist referral for specific red flags such as unexplained hypogonadism, refractory vitamin D deficiency, persistent hypercalcemia, or renal impairment. The immediate first-line evaluation typically includes a DXA scan for bone mineral density, serum calcium, creatinine with eGFR, 25-hydroxyvitamin D, thyroid-stimulating hormone and basic metabolic panel to identify common reversible contributors. Initial assessment prioritizes reversible causes before initiating long-term antiresorptive therapy.

Mechanistically, this approach works because objective measures (DXA and FRAX) quantify fracture risk while labs identify reversible metabolic, endocrine, gastrointestinal, hematologic and medication-related drivers. First-line tests for osteoporosis causes include CBC, CMP (with creatinine and corrected calcium), TSH, 25-hydroxyvitamin D, PTH when calcium abnormal, and celiac serology; second-line testing may add 24-hour urine calcium, serum and urine protein electrophoresis, morning cortisol, and sex hormone levels guided by clinical context. Using WHO T-scores, FRAX probability, and a staged testing framework reduces unnecessary broad panels and aligns evaluation of bone density secondary causes with targeted management, and medication history.

A common clinical error is conflating postmenopausal bone loss with secondary osteoporosis causes and ordering indiscriminate large lab panels; instead, test selection should be driven by patient age and phenotype. For example, premenopausal women with a T-score ≤ −2.5 or unexplained fragility fracture merit earlier evaluation for endocrine causes of osteoporosis such as hypogonadism or hyperthyroidism, malabsorption (celiac disease), eating disorders, and glucocorticoid exposure. Refer to endocrinology for unexplained hypogonadism or persistent hypercalcemia (serum calcium >11 mg/dL), to nephrology when eGFR falls below 30 mL/min/1.73 m2, and to hematology if electrophoresis suggests monoclonal gammopathy. Persistent 25-hydroxyvitamin D levels below 12 ng/mL despite adherence or incident fracture while on antiresorptive therapy also warrant specialist evaluation; medication review (long-term glucocorticoids, aromatase inhibitors, anticonvulsants) often explains secondary causes and guides testing choice.

In practice, initiate an evidence-based sequence: confirm low BMD with DXA, calculate FRAX where appropriate, order first-line labs, and proceed to targeted second-line tests when abnormalities or clinical red flags appear. Medication review for bisphosphonates, aromatase inhibitors, anticonvulsants and glucocorticoids should occur early because drugs are a common secondary cause. Refer to endocrinology for hypogonadism or primary hyperparathyroidism, gastroenterology for malabsorption including celiac disease, hematology for suspected myeloma, and nephrology for eGFR <30 mL/min/1.73 m2. These thresholds help standardize referral decisions. The page that follows provides a structured, step-by-step framework pairing specific tests with numeric referral thresholds across life stages.