Use T and z scores to talk about bone density.(Gynecology)

SAN FRANCISCO -- Patients receiving bone densitometry should be counseled about their T and the z scores, Steven T. Harris, M.D., advised at a meeting on osteoporosis sponsored by the University of California, San Francisco.

The T score compares the patient's bone mineral density with the mean peak bone density of a 30-year-old person of the same sex and is expressed as a number of standard deviations above or below the young person's density, said Dr. Harris of the university.

The z score compares the patient's bone mineral density with mean peak density for someone the same age, and helps give patients some perspective. "In my consultative practice over the years, I've seen many, many, many patients who have been terrified by being told that they have osteoporosis at age 78 by comparing them to that 30-year-old, and yet who feel reassured when you show them where they are relative to their peers," he said.

Sharing both score types helps give patients a more accurate picture of their bone health. A 55-year-old woman with a z score of -2 has bone density around the lower limits of normal for her age, but her T score would be -3.2 in comparison with a young adult. That patient can be reassured that she's similar to her peers, but should be persuaded that "there is an issue here that needs to be addressed," he said.

That said, the patient with a T score above -2.5 (the cutoff for osteoporosis) can still have a clinical diagnosis of osteoporosis if other factors are present such as atraumatic vertebral fractures.

Getting a z score can be especially motivating because those patients who are abnormal, compared with their peers, need the greatest attention to possible secondary causes of low bone density. "If you see an abnormal z score, it makes you worry that much more about something very unusual going on in that particular patient," Dr. Harris said.

Patients should also be warned that first bone ...