DEXA (Dual-energy X-ray absorptiometry) scan

Dual energy X-ray absorptiometry (DEXA or DXA) scans are used to assess and monitor body composition changes. The test is painless, takes about fine to ten minutes, and requires only that the patient lie on an exam table as the scanner directs X-ray energy to the part of the body being imaged. The energy beam passes through the body, but as with a chest X-ray, nothing is actually felt by the patient. The amount of radiation is minimal, about 1/30th of what is received from an X-ray.

DEXA is commonly used to identify people with osteopenia (thinning bones) or osteoporosis (porous, fragile bones), by determining the amount of minerals (calcium and phosphate) present in bone. The bone mineral density (BMD) is arrived at by taking measurements of the spine and hips. One large meta-analysis concluded that the prevalence of osteoporosis in HIV-positive people is three times greater than that found in those who are HIV-negative. The prevalence goes up among HIV-positive people who are on ARV treatment.¹

In addition to measuring bone loss, DEXA is used to assess lipodystrophy (a syndrome including peripheral lipoatrophy, central fat accumulation, and lipomatosis).² Lipoatrophy is a disorder of adipose (fatty) tissue characterised by a selective loss of fat in some areas of the body (e.g. the face). Lipomatosis is a condition in which there are diffuse deposits of fat beneath the skin of the neck, upper trunk, arms, and legs. DEXA, in particular, is used to assess peripheral and truncal fat.

A diagnosis of lipodystrophy may lead to a review of the antiretroviral regimen, as some drugs have been particularly associated with fat loss. Diagnosis of thinning bones can lead to interventions to prevent further bone deterioration. DEXA scans may also help doctors better understand these conditions in people with HIV infection.