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Findings suggest that repeat measurements of bone density in older adults can be delayed for intervals of up to five years in the absence of risk factors for bone loss.

Findings from the Canadian Multicentre Osteoporosis Study suggest that repeat measurements of bone density in middle-aged and older adults can be delayed for intervals of up to five years in the absence of risk factors for bone loss.

In their prospective study, Dr. David Goltzman at Royal Victoria Hospital in Montreal and colleagues examined rates of change in bone mineral density (BMD) as a function of age among randomly selected community-dwelling women (n = 4433) and men (n = 1935), aged 25-85 years. Subjects treated with oral or parenteral glucocorticoids for longer than three months were excluded.

Baseline assessments between 1995 and 1997 were repeated after five years, except for subjects aged 40-60 at baseline who had follow-up examinations after three years. Dual energy x-ray absorptiometry was used to measure BMD of the spine (lumbar vertebrae L1-L4), femoral neck and total hip.

They found that between ages 25 and 40, bone mass is relatively stable in women. BMD begins to fall between ages 40 and 44, with the greatest rate of decline between ages 50 and 54, followed by a slower decline.

Bone loss starts earlier in men, the investigators report, with a steady rate of decline first observed between 25 and 39 years of age.

A second stage of accelerated bone loss at the hip occurs in old age, beginning after age 70 in women and after age 65 in men.

"Although current guidelines recommend that measurements of bone density be repeated once every two to three years, our data suggest that, at this rate of testing, the average person would exhibit changes well below the margin of error," even during periods of peak bone loss, Dr. Goltzman's group states.

They therefore suggest that "repeat measurements of bone density could safely be delayed for intervals of up to five years unless a therapeutic intervention is being monitored or there are additional clinical risk factors for bone loss, such as corticosteroid use."

Although the study documents the benefits of antiresorptive therapy for preserving BMD, Dr. Mark S. Cooper at the University of Birmingham, UK, points out in an editorial that treatment should not be based on BMD alone.

He advocates using the World Health Organization's web-based application - the FRAX algorithm - which computes ten-year fracture probability based on a patient's risk factors, including age, race, body mass index, bone density, behavioral risk factors, and health history. It can be accessed at http://www.shef.ac.uk/FRAX/

CMAJ 2008;178:1660-1668,1683-1684