FREQUENCY OF DISCORDANCE BETWEEN SPINE AND HIP T-SCORE DETERMINED ON DUAL X-RAY ABSORPTIOMETRY (DXA)

Abstract

Aims: Diagnostic discordance for osteoporosis is the observation that T-score of an individual patient varies between skeletal sites, falling into two different diagnostic categories defined by the World Health Organization (WHO) classification system. The principle aim of the study was to examine the frequency of T-score discordance between the hip and lumbar spine using dual energy X-ray absorptiometry (DXA).

Methods: This is a cross-sectional study conducted from 14^th July 2008 till 14^th January 2009 at National Guards Health Affairs Hospital, King Abdulaziz Medical City, Saudi Arabia. BMD images for 692 female patients were searched for various combinations of T-scores reflecting the nine possible discordant and concordant premutations of normal, osteopenia, and osteoporosis. The WHO diagnostic classification system for osteoporosis categorizes patients into three diagnoses----normal, osteopenia, or osteoporosis----based on their T-scores. Concordance was defined as present when the spine and hip T-score placed the patient in the same diagnostic class. Minor discordance was defined as present when the difference between two sites is no more than one WHO diagnostic class. Major discordance was defined as present when one site is osteoporotic and the other site is normal.

Results:  Out of 692 participants (mean age 57.6 ± 9.92 years), major discordance, minor discordance, and concordance of T-scores were seen in 4.5%, 39% and 56.5%, respectively. Most common major discordance observed was osteoporosis of spine and normal hip T-scores while most common minor discordance was osteopenia of spine and normal total hip T-scores.

Conclusion: T-score concordance between the hip and PA L1-L4 spine measurement is the most likely finding, discordance is also a common occurrence. This phenomenon of T-score discordance should be regarded as a real and prevalent finding.