Checking this patient's serum thyroid-stimulating hormone (TSH) level would be the most appropriate test to obtain prior to initiation of pharmacologic therapy. Although osteoporosis in postmenopausal women is most commonly associated with nonmodifiable risk factors such as age, sex, menopausal status, height, and build, it is always important to assess for possible secondary causes of bone loss that might be amenable to treatment, particularly if there is clinical suspicion in a specific patient. Appropriate laboratory testing for most patients with newly diagnosed osteoporosis includes complete blood count (for malignancy), complete metabolic profile (for calcium levels and kidney function), TSH, 25-hydroxyvitamin D, and urine calcium (screening for hypercalciuria), most of which were normal in this patient. However, this patient's history of unintentional weight loss over the past year may be her only symptom of hyperthyroidism, which could be contributing to her osteoporosis and would be important to treat in addition to therapy directed toward her osteoporosis. Therefore, measuring this patient's TSH level would be appropriate prior to starting therapy for osteoporosis.

Both serum and urine markers of bone turnover measure collagen breakdown products and other chemicals released from osteoclasts and osteoblasts as part of bone metabolism. However, they are not commonly used in most patients with osteoporosis primarily because there is significant variability in the different measures in an individual patient or between different patients, making standardization of results difficult. Therefore, their use is typically limited to research settings or in management of specific patients who have failed to respond to usual therapy for osteoporosis.

There is evidence that estrogen is effective for prevention and possibly treatment for osteoporosis, although the significant nonskeletal risks associated with this therapy have led to its not being used in favor of bisphosphonates. As this patient is postmenopausal and has no clinical suggestion of excess estradiol secretion, and bisphosphonate therapy would be considered preferable to estrogen despite serum levels, testing for estradiol would not be indicated in this patient.

Hyperparathyroidism should always be considered as a possible secondary cause of bone loss. However, since this patient had normal calcium and 25-hydroxyvitamin D levels, hyperparathyroidism would be highly unlikely, and checking a parathyroid hormone level would not be indicated.