The accuracy of peripheral bone densitometry, the most commonly used diagnostic tool for diagnosing osteoporosis, has come under fire.

The first problem is that the human body doesn't always play ball. Bone mineral density (BMD) is not uniform throughout the skeleton. Just measuring at two sites usually the hip and spine does not give a full picture of the skeleton. Also, while the World Health Organization has set criteria for a healthy BMD, these apply only to the hip and spine. Elsewhere in the body, there is a wide range of 'normal' BMD which may be misdiagnosed as abnormal when only WHO criteria are used.

The other problem is that measuring devices perform differently. Many practitioners favour the newer ultrasound machines because they are less expensive and more portable. However, these newer machines cannot diagnose osteoporosis because they do not measure BMD (on which, according to the WHO, the diagnosis of osteoporosis must be made). Instead, ultrasound does measure other factors related to bone strength.

Researchers warn that making a diagnosis of osteoporosis is still not an exact science and that women should be aware of the strong possibility of being misclassified, particularly when the test is performed before the age of 65 (BMJ, 2000; 321: 396-7).