DXA Bone Density Testing: Understanding Your Results

“My report has a negative number. Does that mean my bones are already very weak?”

A bone density report can be confusing. It may list several parts of the body, different scores, and color-coded categories. A clear explanation of the scores can help you understand your bone health and plan the next steps in care.

This guide explains the main questions to bring to the appointment where your results are reviewed. A report is most useful when it leads to a clear understanding of your bone health and the next step.

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What does DXA measure?

DXA stands for dual-energy X-ray absorptiometry. You may also see it written as DEXA. It uses a low dose of X-rays to measure bone mineral density, commonly at the hip and lower spine. It is a standard tool for assessing osteoporosis and following bone density over time.

The test is noninvasive and does not normally require anesthesia. You lie on a scanning table while the technologist positions you and obtains the measurements. Tell the facility beforehand if you have difficulty lying flat or positioning your hip.

A DXA scan and an ordinary X-ray answer different questions. An X-ray can identify fractures and other structural problems; it does not provide the same standardized bone density measurement. A previous X-ray or a general health check therefore does not tell you whether you have had an appropriate osteoporosis assessment. ACR/RSNA patient information

Who should discuss having a bone density test?

The International Society for Clinical Densitometry lists women aged 65 and older and men aged 70 and older among the groups for whom testing is indicated. Earlier testing can be appropriate when relevant risk factors are present, such as a previous fragility fracture, low body weight, a disease associated with bone loss, or certain medicines. ISCD testing indications

When discussing testing, mention previous fractures, changes in height, illnesses, and current or past medicines. Bring any previous reports. If you are preparing for joint replacement, also ask how bone health assessment fits into the surgical plan.

The results can help guide further assessment, treatment, and follow-up.

Prepare so the measurement can be interpreted properly

Follow the scanning center’s instructions. RadiologyInfo advises avoiding calcium supplements for at least 24 hours before the examination; confirm this with your own facility. This is a preparation instruction, not a recommendation to stop long-term treatment.

Tell the team if you might be pregnant, have recently had an examination involving contrast or barium, or have metal implants or prior spine surgery. These details may affect scheduling, positioning, or interpretation. Wear suitable clothing and follow instructions about removing metal objects in the scan area. Preparation information

Also make sure the recorded personal information is correct. Bring the reason for the referral and previous scans if available. This helps the clinician understand whether the aim is an initial assessment, treatment follow-up, or investigation of a new concern.

T-scores: comparison with a young-adult reference

A T-score expresses how your bone density compares with a young-adult reference population. It is measured in standard deviations. It is not the percentage of bone you have lost or the percentage chance that you will fracture a bone.

For postmenopausal women and men aged 50 and older, the usual densitometric categories are:

T-score at a valid diagnostic site	Category
−1.0 or higher	Normal bone density
Lower than −1.0 but higher than −2.5	Low bone mass, often called osteopenia
−2.5 or lower	Osteoporosis

Your clinician reviews the scan images and uses appropriate measurement sites, accounting for implants or structural changes that may affect the result. ISCD diagnostic positions

Z-scores: comparison with people of similar age

A Z-score compares your result with an age-appropriate reference. Z-scores are generally preferred for premenopausal women and men younger than 50.

A Z-score of −2.0 or lower is described as below the expected range for age; a score above −2.0 is within the expected range. The phrase describes a comparison and needs clinical interpretation. In particular, osteoporosis in younger men cannot be diagnosed from bone density alone.

If you are younger and have a low result, the appointment should explore its context: your history, fractures, health conditions, medicines, and other possible explanations. Do not assume that the treatment decision is identical to that for an older person with the same-looking number. ISCD reporting positions

Why are there different values for the hip and spine?

DXA measures specified areas rather than producing a single direct measurement of every bone. Your report may include the lumbar spine, total hip, and femoral neck. The clinician reviews the valid measurements together.

Spine degeneration, a vertebral fracture, surgical hardware, or a hip implant can affect interpretation. Sometimes an affected area is excluded, or another appropriate site is used. The image and the measurement belong together; interpretation is more than reading a table of numbers.

If you have a hip replacement, tell the technologist which side was operated on. Ordinary osteoporosis measurement through an artificial hip is different from specialized DXA used to examine bone around an implant. Bone density assessment can usually be arranged using other appropriate sites.

Ask the clinician to identify which sites were valid and which result guided the conclusion. If a site could not be used, ask how the assessment was completed.

Does the category determine whether I need medicine?

A density category is part of the assessment. A treatment decision also considers fracture history, other risk factors, medical conditions, and applicable clinical guidance. A person with low bone mass may still need a careful fracture-risk evaluation; a normal result is considered alongside falls and other clinical factors.

Ask two separate questions: “What does the scan show?” and “What does that mean for my treatment?” That makes it easier to understand why recommendations may differ between people whose reports look similar.

If medication is proposed, discuss its purpose, how it will be used, its risks, and the follow-up plan. If medication is not proposed, ask what care and reassessment are appropriate. Either conversation should result in a practical plan rather than simply a label.

Following change over time

Repeat scans help track bone density over time. Your clinician checks the size of any change and whether the measurements can be reliably compared.

The reporting team uses a concept called least significant change to judge whether a difference is large enough to exceed expected measurement variation. You do not need to calculate it yourself; ask whether the report identifies a meaningful change.

Measurements from different machines or facilities may not be directly comparable unless suitable cross-calibration has been performed. Bring the older report and, where available, the images. The clinician can decide whether a valid comparison is possible.

The timing of your next scan reflects the purpose of testing, baseline findings, treatment, new fractures, and factors that could change bone density. A repeat scan is most useful when it can inform care. ISCD follow-up and comparison positions

A short checklist for reviewing your report

Which result applies to me: T-score or Z-score?
Which measurement sites were valid?
Does my fracture history change the interpretation?
Do my medicines or medical conditions need further review?
If this is a repeat scan, is the change meaningful and comparable?
What should I do next, and who will follow up?

Take the answers home with the report. A family member helping with care should be able to understand the plan without trying to interpret every line of the printout.

Frequently asked questions

Do I need to fast?

Fasting is generally not required for DXA alone, but follow the facility’s instructions, especially if other tests are scheduled. Ask specifically about calcium supplements and recent contrast examinations.

Is a more negative T-score a percentage of bone loss?

No. It is a standardized comparison with a reference population. It should not be converted directly into “percent of bone remaining.”

I am young. Should I focus on the T-score?

In premenopausal women and men under 50, the Z-score is generally the preferred comparison. A clinician should interpret low density with the broader history rather than apply an older-adult label automatically.

Can I have a scan if I have an artificial hip?

Yes, assessment can usually be planned using appropriate sites. Tell the team about the implant before the examination so that unsuitable measurements are not used for routine osteoporosis diagnosis.

Can spinal degeneration affect the result?

Yes. Structural changes can interfere with measurement. The clinician reviews the scan image and decides which areas can be interpreted, rather than relying only on the reported score.

Can I compare numbers from two hospitals?

Bring both reports. Your clinician can check whether the machines and measurement methods allow a reliable comparison.

Should I repeat the test every year?

Your clinician can recommend the next scan based on your initial result, treatment, and any changes in your health.

If the result is normal, am I protected from fractures?

A normal result is encouraging. Keeping your bones healthy also involves attention to falls, previous fractures, nutrition, and other clinical factors.

A note from Dr. Tai

A useful bone density assessment ends with an explanation you can understand. Before leaving, make sure you know what the result means for you, whether anything needs treatment or further investigation, and when the plan will be reviewed.

Medical information disclaimer

This article provides general education for adults. It does not diagnose osteoporosis or determine treatment from a report alone. Your age, fracture history, medical conditions, scan quality, and local clinical guidance must be considered by your clinician.

References

Written by Ta-Wei Tai, MD, PhD, hip and knee surgeon at National Cheng Kung University Hospital, Tainan, Taiwan. Author profile: Mandarin page.