DEXA stands for dual energy X-ray absorptiometry and determines bone density. Bone blocks the low energy X-rays; the denser the bone, the fewer X-rays that will pass through it. DEXA scans are requested to determine the strength of the bone, and are often used in patients who are at an increased risk of osteoporosis, or thinning of the bones. Such patients include post-menopausal women, those who have undergone steroid use and people with low body mass index or recurrent fractures. There are two forms of DEXA scanning machine: one that scans peripheral bones such as the heel or fingers and one that measures the central skeleton such as hips and vertebrae. The amount of X-rays that pass through the bone is detected, and a computer calculates the scores.
Find the column marked BMD. This stands for bone mineral density and is the number of grams per centimetre of bone. The greater the number, the stronger the bone. However, because BMD is calculated by using area, it is not always an accurate measurement.
Find the column labelled "T score." This score compares the individual's T score with the average bone mineral density of a 30-year-old of the same sex and ethnicity. Thirty is the peak age for bone density. A score of zero means that the BMD is equal to that of a 30-year-old. The difference between the 30-year-old and the patient is measured in standard deviations, which indicate the variability from the average. Scores of -1 or higher are normal, scores between -1 and -2.5 indicate thinning bones and scores of less than -2.5 indicate osteoporosis.
Find the column labelled "Z score." This compares the individual's bone mineral density with that of a person the same age, sex and ethnicity. It can indicate an underlying disease or disorder that is causing the low bone density.
View the scan. Artefacts and abnormal bone structure can cause inaccurate results and should be taken into account. Repeat scans should be taken from the same area to be able to accurately determine changes.
All results should be discussed with the medical practitioner.
Tips and warnings
- All results should be discussed with the medical practitioner.