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Am Fam Physician. 2003;67(4):873

Osteoporosis, or low bone density, most commonly results from estrogen-deficiency bone loss and age-related bone and mineral metabolism changes. Identification of contributing asymptomatic mineral and metabolic conditions results in more effective treatment of low bone density. Routine laboratory testing of women with osteoporosis can identify some of these disorders, but no evidence-based guidelines indicate which tests should be done. Tannenbaum and associates used a cross-sectional chart review to determine the prevalence of undetected disorders that could affect bone and mineral metabolism, which were identified by laboratory testing in healthy post-menopausal women recently diagnosed with osteoporosis.

The study participants were self-referred or referred by a primary care physician for management of decreased bone density. Women with known disorders that could affect bone or mineral metabolism and those taking drugs that impair bone health were excluded. Previously undiagnosed disorders were identified by laboratory testing using standard criteria.

Complete laboratory data were available for 173 women with a mean age of 65.5 years. Fifty-five women were determined to have a total of 56 previously undetected disorders that could have an impact on bone or mineral metabolism. The most common disorder noted was hyper-calciuria, followed by malabsorption, hyperparathyroidism, vitamin D deficiency, exogenous hyperthyroidism, Cushing's disease, and hypocalciuric hypercalcemia. The only significant predictors of the presence of an undiagnosed disorder of bone or mineral metabolism were a history of localized breast cancer and a history of smoking. By analyzing the yield of the different combinations of diagnostic tests, various strategies could be evaluated.

The authors conclude that because undiagnosed disorders of bone or mineral metabolism are present in up to one third of healthy women with osteoporosis, further laboratory screening may be appropriate. A basic screen consisting of determination of serum calcium levels, serum parathyroid hormone levels, and 24-hour urinary calcium excretion (with the addition of serum thyroid-stimulating hormone level in women receiving thyroid replacement therapy) offers a high diagnostic yield at an acceptable cost for women with osteoporosis who are otherwise healthy and actively receiving primary care. Further prospective studies are needed to confirm these results and determine appropriate laboratory screening in women with low bone density who are not being treated by a primary care physician or who have major risk factors for bone disease based on a pre-existing condition.

In an editorial in the same journal, Wagman and Marcus support the need for a testing algorithm for women with osteoporosis, but they note the difficulty in obtaining and standardizing 24-hour urine calcium excretion. They agree that further studies will clarify the appropriate testing strategy.

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