T-Scores for Diagnosing Osteoporosis: 3 Are Better Than 1

This post comes from Fred Nelson, MD, an orthopaedic surgeon in the Department of Orthopedics at Henry Ford Hospital and a clinical associate professor at Wayne State Medical School. Some of Dr. Nelson’s tips go out weekly to more than 3,000 members of the Orthopaedic Research Society (ORS), and all are distributed to more than 30 orthopaedic residency programs. Those not sent to the ORS are periodically reposted in OrthoBuzz with the permission of Dr. Nelson.

The World Health Organization (WHO) and the International Society for Clinical Densitometry (ISCD) define osteoporosis based on (DXA) measures of bone mineral density that are translated into T-scores. A T-score ≤ -2.5 at any 1 of the 3 commonly measured sites (lumbar vertebrae, femoral neck, and total hip) is considered diagnostic for osteoporosis, and a T-score between -2.5 and -1 is indicative of osteopenia. University of Pennsylvania investigators1 proposed that combining all 3 T-scores in a multivariate analysis would be “potentially more informative” than the common practice of using the single lowest T-score.

The investigators applied multivariate statistical theory to T-scores from a sample of 1,000 65-year-old white women. When both real data and simulation models were analyzed, the researchers found that more patients were diagnosed with osteoporosis using the multivariate version of the WHO/ISCD guidelines than with the current WHO/ISCD guidelines. The diagnoses of osteoporosis using this method were also associated with higher Fracture Risk Assessment Tool (FRAX) probabilities of major osteoporotic fractures (P=0.001) and hip fractures (P=2.2×10−6). The FRAX tool combines a patient’s history of fracture with age, sex, race, height, weight, and social habits such as smoking and drinking to determine the risk of a major facture in the next 10 years.

This study shows that statistically considering all 3 T-scores may reveal more cases of osteoporosis than using the single lowest T-score. The trick will be getting this insight into the hands—and minds—of those making radiologic interpretations of DXA findings.

Reference 

  1. Sebro R, Ashok S. A Statistical Approach regarding the Diagnosis of Osteoporosis and Osteopenia from DXA: Are we underdiagnosing osteoporosis? J. Bone Mineral Res Plus. In press

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