FDA Seeks to End T-Score Disparities.

VAIL, COLO. -- Big changes are afoot in how bone mineral density is used to diagnose osteoporosis.

The Food and Drug Administration has decided that the present situation must go; it's unacceptable to have 26 bone mineral density measurement devices on the market worldwide that provide different T scores when used to measure the same patient at the same anatomic site.

The practical clinical problem created by this "T-score discrepancy," as it's known within the field, is that it's not uncommon for a patient to be diagnosed as having osteoporosis based upon bone mineral density (BMD) measurement with one device while an essentially identical patient tested using another device is found not to have osteoporosis, Dr. Paul D. Miller explained at a conference on obstetrics and gynecology sponsored by the University of Colorado.

The reason for the T-score discrepancy is that every manufacturer bases its machine's T-score cutoff on its own reference database of young normal women, and these databases aren't consistent.

The FDA has opted for a two-pronged solution. On a short-term basis, the answer is to establish T-score equivalence between all marketed devices. This has tentatively been accomplished using data from the Study of Osteoporotic Fractures (SOF), the largest U.S. prospective fracture database. These T-score equivalence recommendations are now in peer review, according to Dr. Miller of the university.

The key recommendation of the T-score equivalence project is that it's time to do away with the current notion that the diagnosis of osteoporosis based upon BMD requires a T score of at least -2.5 standard deviations (SD) at whatever site is measured.

For example, using SOF data, the T-score equivalence working group chaired by Dr. Dennis Black of the University of California, San Francisco, determined that 70-year-olds having a T score of -2.5 SD at the femoral neck by dual energy x-ray absorptiometry have a 6% risk of hip fracture over the next 5 years, which fulfills the World Health Organization definition of osteoporosis.