How to read a bone densitometry report

How to read a bone densitometry report?

• T-score: The number of standard deviations (SD) the patient is below or above the mean value for young (30 years) normal subjects (peak bone mass). The T-score is a good predictor of the fracture risk

• Z-score: The number of SD the patient is below or above the mean value for age-matched normal subjects. The Z-score indicates whether or not the BMD is appropriate for age. A low Z-score is predictive of an underlying secondary cause other than age or menopause.
• Absolute BMD: The actual BMD expressed in g/cm ² . This is the value that should be used to calculate changes in BMD during longitudinal follow-up.

After a World Health Organization report published in 1994, osteoporosis is often diagnosed on the basis of the patient’s T-score value (difference of BMD from young adult mean normalized to the population SD). T-scores are a measure of current fracture risk.

There are problems relating to the use of T-scores in the elderly, and we argue that decisions about treatment are generally best made on the basis of the Z-score value (difference of BMD from age-matched mean normalized to the population SD) because this measures the patient’s fracture risk relative to his or her peers.

Recent studies confirm that the posteroanterior (PA) projection lumbar spine scan is still the optimum measurement site for monitoring response to treatment. A BMD change of 4.5% is required to register a statistically significant change.

Sources

1.Interpretation of bone densitometry studies

2. Krugh M, Langaker MD. Dual-Energy X-Ray Absorptiometry. [Updated 2024 May 20]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK519042/https://www.ncbi.nlm.nih.gov/books/NBK519042/