Concerning the Article: Should Q-CT Be the Gold Standard for Detecting Spinal Osteoporosis?

TO THE EDITOR: Concerning the Article: Should Q-CT Be the Gold Standard for Detecting Spinal Osteoporosis? Arvind compared the T-scores of the bone densities measured by two different methods: spinal quantitative computed tomography (QCT) and dual-x ray absorptiometry (DXA). The diagnostic criteria recommended by the WHO in 1994 was used to establish the diagnosis of osteoporosis (normal, −1.0 or above; osteopenia, between −1.0 and −2.5; osteoporosis, −2.5 or below). The author concluded that QCT provides more precise estimation of cancellous bone mineral density (BMD) than DXA. We would like to comment on the most relevant shortcomings. The T=−2.5 criterion introduced by WHO is primarily based on the relationship between forearm BMD (tested by DXA) and prevalent hip fracture. It is inappropriate to use a −2.5 T-score for different measurement techniques.1 Instead, the following diagnostic cut points may be used for assigning a spine QCT (normal, BMD >120 mg/cm3; osteopenia, 80 mg/cm3 ≤BMD ≤120 mg/cm3; osteoporosis, BMD <80 mg/cm3).2 A DXA T-score of −2.5 would correspond to an equivalent QCT T-score of −3.4 using reference data published for the scanner manufacturer (Siemens) and analysis mode.3 For these reasons, Arvind assigning a T=−2.5 diagnostic category based on a QCT spine T-score will likely result in overestimating osteoporosis patients.