Clinical utility of laboratory testing in women with osteoporosis.

Clinicians regularly order laboratory tests in women with osteoporosis to assess if an underlying medical condition is contributing to bone loss. To determine which laboratory tests are associated with osteoporosis we conducted a secondary analyses of data collected as part of the Fracture Intervention Trial (FIT), which included 15,316 postmenopausal women. Women had tests of liver and kidney function, mineral metabolism, electrolytes and complete blood count, femoral neck and total body BMD and spinal radiographs. The prevalence of abnormal tests in women with osteoporosis compared to women without was not different, except for low TSH (<0.5 IU/ml). Among women with and without osteoporosis at the femoral neck the prevalence of low TSH was 4.9% (95% CI: 4.4-5.5) and 3.7% (95% CI: 3.3-4.1), respectively, yielding a positive likelihood ratio of 1.2 (95% CI: 1.1-1.3). We observed similar results for women with vertebral fractures compared to women without vertebral fractures; positive likelihood ratio of 1.4 (95% CI: 1.3-1.6). Our data suggests that when assessing healthy women with osteoporosis ordering a routine panel of laboratory tests is not useful but measuring TSH may be informative.