A useful report conversation starts with three details: the exact measurement, the units and the reason the scan was performed. Keep those details beside the number as you read. The reference material below explains how published comparisons work; it cannot decide whether your individual result needs treatment.
If your report uses a different scanner, region or reference population, ask the clinic which comparison applies. Avoid substituting a convenient online table just because the units look similar. Discuss bone density or visceral fat findings with your GP.
Read the measurement
A Z-score compares a bone density measurement with an age-matched reference. It is expressed in standard deviations, not a percentage and not a diagnosis.
| Z-score | ISCD wording |
|---|---|
| -2.0 or lower | Below the expected range for age |
| Above -2.0 | Within the expected range for age |
A reference comparison, not a percentage
A Z-score of zero is at the reference mean. A negative number is below that mean and a positive number is above it. A Z-score of -1 does not mean that bone density is one per cent low, or that someone has lost a fixed amount of bone. The scale reflects the reference distribution.
Z-scores and percentiles both describe comparison with a reference, but they are not interchangeable labels. The relationship depends on the distribution and the method used. Copy the score exactly as reported instead of turning it into a percentage without the appropriate reference calculation.
When Z-scores are preferred
ISCD prefers Z-scores rather than T-scores in women before menopause and men younger than 50. The terminology also differs: a Z-score of -2.0 or lower is described as below the expected range for age, while a value above -2.0 is within the expected range for age.
This wording should not be replaced with T-score category names. In particular, osteoporosis cannot be diagnosed in men under 50 using BMD alone. The practitioner needs the clinical setting and other findings. Children require a separate paediatric approach and are outside these adult explanations.
What does a Z-score of -1 mean?
It means the measurement is one standard deviation below the selected age-matched mean. Under the adult terminology above, that number is within the expected range for age. It does not provide an all-clear for every bone-health concern, and it does not diagnose low bone mass using the T-score bands.
If the score was unexpected, ask about the measured site, the reference database and the report’s conclusion. The clinic can check whether age and other relevant demographic inputs were entered correctly. A useful discussion starts with the whole report rather than a single signed number.
Comparisons between visits
An age-matched score can change partly because the reference comparison changes as someone gets older. Keep the absolute BMD value, scan site and scanner details as well as the score. A change in Z-score alone is not a direct measure of kilograms or percentage of bone gained.
The facility’s measurement precision and cross-calibration rules apply to follow-up bone density. Ask whether an observed BMD difference reaches the facility’s least significant change. A different scanner or database may make score comparisons misleading even when the printed numbers look similar.
Discuss bone density findings with your GP, especially when the report flags an unexpected value or you have relevant fracture or health history. The scan is a measurement used in an assessment. The appropriate next step may be clarification of the report, review of other risk factors or further clinical investigation rather than simply repeating the scan.
Questions for your practitioner
- Is Z-score the appropriate comparison for my age and circumstances?
- Which site and age-matched database were used?
- What does the report conclusion mean alongside my history?
Sources checked 23 September 2026: Source 1 · Source 2. New reference material prepared by DEXA Scans Australia; not included in Kristof’s earlier review.
Common questions about results
What is a good body fat percentage on a DEXA scan?
There is no single percentage that suits everyone. Published tables describe a reference population, not a target. Check the scanner, age group and sex group, then discuss the result alongside your health, strength, nutrition and reason for testing.
Why is my DEXA percentage different from my smart scale?
DEXA and bioimpedance scales estimate body compartments using different measurements and assumptions. Hydration and preparation can also affect comparisons. Neither an automatic correction factor nor combining both methods into one trend is reliable.
What does ALMI mean?
Appendicular lean mass index is arm and leg lean tissue divided by height in metres squared. It is one measure of muscle quantity. It does not measure strength and cannot diagnose sarcopenia by itself.
Is a Z-score of -1 bad?
ISCD describes adult Z-scores above -2.0 as within the expected range for age. That wording is a reference comparison, not a complete assessment of bone health. Ask your GP about the scan site, report conclusion and your medical history.
How often should I have another scan?
Agree on an interval that answers a useful clinical or training question. The reason for testing, expected change, scanner precision and whether the scan is for bone density or body composition all matter. There is no universal schedule for everyone.
Does lean mass mean muscle mass?
No. Lean soft tissue includes water and organs as well as muscle. Bone mineral content is reported separately. A change in lean tissue can reflect more than a change in muscle.
Can I compare results from GE and Hologic?
Do not treat values from different scanner families as interchangeable. Software, calibration, region definitions and reference databases differ. Ask the clinic whether a meaningful comparison is possible before interpreting a change.
Does a whole-body scan diagnose osteoporosis?
A body composition scan is not a substitute for a diagnostic bone density assessment at appropriate sites. Your GP or specialist interprets bone health findings alongside age, menopause status, fracture history and other relevant information.
How do I know if a change is larger than measurement variation?
Ask the clinic for its least significant change for the measurement. At 95% confidence, the usual calculation is 2.77 times measured precision error. Our calculator is an illustration and cannot replace the clinic’s precision assessment or confirm why a number changed.
Keep the result useful
Save the original report, including its scanner details and reference notes. At a later appointment, bring the earlier copy rather than relying on a rounded value entered in an app. Ask whether preparation, positioning and software were comparable, and whether the change is large enough to influence the decision you are making.
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