Some Abdominal CT Scans May Help ID Osteoporosis

CT scans of the abdomen ordered for other purposes, but that include the lumbar spine, can help screen patients for osteoporosis, according to a study published in the Annals of Internal Medicine.

Although dual-energy X-ray absorptiometry (DXA) is the standard for detecting osteoporosis, not all women are able to undergo a DXA and may never undergo bone mineral density (BMD) testing. Researchers from the University of Wisconsin School of Medicine and Public Health undertook a study to compare CT-derived BMD assessments with DXA measures to see if they could identify osteoporosis by using CT scans performed for other clinical indications.

The researchers assessed the CT and DXA findings of 1,867 adults (2,067 pairs). They found that CT-attenuation values were significantly lower at all vertebral levels for patients with DXA-defined osteoporosis. An L1 CT-attenuation threshold of 160 Hounsfield units (HU) or less was 90 percent sensitive and a threshold of 110 HU was more than 90 percent specific for distinguishing osteoporosis from osteopenia and normal BMD.

Positive predictive values for osteoporosis were 68 percent or greater at L1 CT-attenuation thresholds less than 100 HU; negative predictive values were 99 percent at thresholds greater than 200 HU. Among 119 patients with at least one moderate-to-severe vertebral fracture, 62 (52.1 percent) had nonosteoporotic T-scores (DXA false-negative results), and most (97 percent) had L1 or mean T12 to L5 vertebral attenuation of 145 HU or less. Similar performance was seen at all vertebral levels. Intravenous contrast did not affect CT performance.

The authors concluded that use of abdominal CT images for reasons other than osteoporosis screening but which include the lumbar spine in the image can be used to identify patients with osteoporosis or normal BMD without additional radiation exposure or cost.

An accompanying editorial finds merit in some of the findings, despite of the study’s limitations. However, Sumit R. Majumdar, MD, MPH, from the Department of Medicine, University of Alberta, wrote that the possible use of CT scans could be to rule in patients with osteoporosis, rather than ruling out patients.