How Is a Bone Density Test Done?
How Is a Bone Density Test Done? Step-by-Step Patient Guide
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A bone density test (also known as a DEXA or DXA scan) is one of the easiest, quickest, and most painless medical screenings you can undergo. It is performed while you lie fully clothed on an open, padded table, as a mechanical arm passes slowly over your body to scan your bones using low-level X-ray technology. Known as the "gold standard" for measuring bone health, this test assesses how strong and dense your bones are, helping to detect osteoporosis or low bone mass (osteopenia) before a fracture occurs (Mayo Clinic, 2023).
If you’ve been advised to get one, you might be picturing a noisy, enclosed MRI tube or a complicated hospital procedure. The reality is much simpler—and far less intimidating. Whether you’re a postmenopausal woman checking her risk factors or an athlete monitoring bone health, knowing exactly what to expect can eliminate anxiety. Here is your complete, step-by-step patient guide to how a bone density test is done.
Quick-Answer Summary
In a rush? Here are the three most common questions patients ask:
- What should I wear? Loose, comfortable clothing without metal (no zippers, buttons, or underwire bras). Gym clothes like leggings and a t-shirt are perfect (see our guide on how clothing impacts your scan).
- How long does it take? The scan itself takes about 6–10 minutes. The entire appointment is usually under 20 minutes.
- Does it hurt? No. The test is non-invasive, painless, and does not involve needles or enclosed tubes (HSS, n.d.).
Part 1: How to Prepare for Your Scan
Preparation for a DEXA scan is minimal compared to other medical tests. You don’t need to fast, and you can drive yourself to and from the appointment. However, there are a few specific rules to ensure your results are accurate.
The "Day Before" Checklist
- Stop Calcium Supplements: If you take calcium, stop taking it 24–48 hours before your exam. Undissolved calcium tablets in your stomach can show up on the scan and look like bone, skewing the data (UnityPoint Health, n.d.).
- Eat Normally: You can eat and drink as usual on the day of the test (unlike some blood work or body composition scans where fasting is recommended).
- Review Medical History: If you have had a barium enema, CT scan with contrast dye, or a nuclear medicine test in the last 14 days, you must reschedule. The contrast dye interferes with the X-ray sensors (UCSF Radiology, n.d.).
What to Wear (and What to Skip)
The goal is to wear clothes that the X-rays can pass through easily without creating "artifacts" (phantom images) on the screen.
✅ DO Wear:
- Elastic-waist pants or leggings
- T-shirts or tops without buttons/snaps
- Sports bras (without metal hooks or underwire)
- Socks (you will likely be asked to remove shoes)
❌ AVOID:
- Jeans with metal rivets or zippers
- Belts and large buckles
- Underwire bras
- Jewelry (necklaces, watches, dangling earrings)
- Clothing with heavy embroidery or metallic threads
Note for BodySpec Clients: At BodySpec, we provide a private changing area if you need to switch into exam-safe clothing, but arriving in "scan-ready" attire saves you time. See more about what to expect during your appointment.
Part 2: The Procedure (Step-by-Step)
Here is a walkthrough of exactly what happens from the moment you walk in until you leave.
Step 1: Arrival & Positioning
After a quick check-in and verifying you aren't wearing metal, you will be taken to the scanner room.
- The Machine: The DEXA scanner looks like a large, padded massage table with a mechanical arm hovering above it. It is open air—not a tunnel or tube.
- Getting on the Table: You will lie flat on your back on the padded table.
- Leg Position: To get the clearest image of your lumbar spine (lower back), the technician may place a firm foam block under your knees. This flattens your lower back against the table. To scan your hips, they may gently rotate your feet inward and secure them with a soft brace to separate the hip bones from the pelvic bowl in the image (MedlinePlus, 2022).
Step 2: The Scan
Once you are positioned, the technician will sit at a computer nearby. You are never left alone in the room.
- Movement: The mechanical arm (the scanner) will slowly move over your body. It passes over your hips and lower spine, which are the two key areas for measuring bone strength.
- Sound: You might hear a quiet whirring or humming sound as the arm moves, but it is much quieter than an MRI.
- Your Job: Your only job is to lie very still and breathe normally. In some clinical settings, you might be asked to hold your breath for a few seconds, but typically, normal shallow breathing is fine.
Step 3: Completion
The machine does not touch you during the scan. The arm moves roughly 12 to 24 inches above your body.
- Duration: The active scanning process usually lasts between 6 to 10 minutes.
- Wrap Up: Once the arm stops moving, the technician will remove the leg support, and you can sit up. There is no dizziness or recovery time required.
What Does It Feel Like?
Many patients worry about claustrophobia or comfort.
- No Claustrophobia: Because the scanner is open strictly on the sides and the arm is relatively small, most people with claustrophobia tolerate DEXA scans very well. You can see the room and the technician the entire time.
- Comfort: The table is padded. If you have severe back pain that makes lying flat difficult, let the technician know. They can often adjust the leg blocks to make you more comfortable.
Is it Safe? (The Radiation Question)
Safety is a top priority for any medical test. A DEXA scan uses X-ray energy, but the amount is extremely low—typically far less than a standard chest X-ray.
- The Comparison: A standard bone density scan exposes you to about 1–5 microsieverts (µSv) of radiation.
- Real-World Context: This is comparable to the unavoidable background radiation you receive from the environment in a single day, or what you would absorb during a short airplane flight (Shepherd et al., 2017).
- Vs. Other Tests: It is a tiny fraction of the dose from a CT scan or mammogram.
Note: Despite the safety, if there is any chance you are pregnant, be sure to inform your technician, as you should postpone the scan.
Whole-Body Wellness Scans vs. Medical Diagnostic Scans
It is important to understand the difference between the whole-body wellness scans provided by BodySpec and the regional diagnostic scans typically ordered by a doctor.
Medical Diagnostic Scans (Central DXA)
When a doctor orders a bone density test to check for osteoporosis, they are usually requesting a "Central DXA" scan. These focus exclusively on the hip and lumbar spine.
- Purpose: To formally diagnose osteoporosis.
- Audience: Typically reserved for women over 65, men over 70, or younger individuals with specific medical risk factors.
- Insurance: Often covered by insurance if you meet age or risk criteria.
BodySpec Wellness Scans (Whole-Body)
BodySpec scans are whole-body screenings. We scan you from head to toe to analyze your total body composition (fat and muscle) along with your bone density.
- Purpose: To provide a comprehensive snapshot of your metabolic and skeletal health. While we measure Bone Mineral Density (BMD) and provide T-scores/Z-scores, these are intended for wellness tracking and early screening rather than formal medical diagnosis.
- Audience: Anyone who wants to proactively monitor their bone strength and body composition, regardless of insurance status.
Why Scores May Differ
If you have a diagnostic scan at a hospital and a wellness scan at BodySpec around the same time, your T-scores or Z-scores might look slightly different. This does not mean one machine is wrong.
- Different Measurements: A diagnostic scan measures density in just the hip and spine. A BodySpec scan measures density across your entire skeleton (or sometimes regional averages derived from the whole body).
- Different Baselines: Variations in how different organizations (like NHANES) calculate reference databases can also lead to slight variances in scores.
Think of a whole-body scan as an excellent "early warning system." It allows you to spot downward trends in bone density decades before you might qualify for a hospital scan, giving you time to adjust your diet and exercise routine.
Understanding Your Results
After your scan, you will receive a report detailing your bone mineral density (BMD). The two most important numbers you will see are the T-Score and the Z-Score.
The T-Score
This compares your bone density to that of a healthy 30-year-old adult (when bone mass is at its peak). According to the National Osteoporosis Foundation, T-scores are interpreted as follows (Bone Health & Osteoporosis Foundation, n.d.):
- -1.0 and above: Normal bone density.
- -1.0 to -2.5: Low bone mass (Osteopenia). This suggests seeing a doctor to discuss prevention strategies.
- -2.5 or lower: Osteoporosis. This indicates significantly fragile bones and a higher risk of fracture.
The Z-Score
This compares your bone density to other people of your same age, sex, and weight. This number helps doctors understand if your bone loss is just due to aging or if something else (like medication or a thyroid issue) might be accelerating it.
FAQ: Common Patient Questions
How often should I get a bone density test?
For most postmenopausal women or high-risk individuals, guidelines often align with Medicare coverage which typically allows for a screening every 24 months (2 years) (USPSTF, 2018). BodySpec clients tracking specific interventions (like weight-bearing exercise or dietary changes) often choose to scan every 3–12 months to monitor trends. Learn more about when to get a DEXA scan.
Why can't I take calcium before the test?
Calcium supplements are dense minerals. If a pill hasn't fully dissolved in your digestive tract, the X-ray might "count" that pill as part of your spine's bone density, leading to an artificially high (inaccurate) score.
Is a BodySpec scan the same as a hospital scan?
BodySpec uses research-grade DEXA scanners similar to those in hospitals—specifically the GE Lunar iDXA (at our storefronts) and the GE Lunar Prodigy (in our mobile vans). However, our reports are designed for information and wellness tracking. While we provide precise T-scores and Z-scores, we do not provide a medical diagnosis or treatment plan. You should always share your BodySpec report with your primary care physician for clinical interpretation.
Take the Next Step for Your Bone Health
Bone health is often invisible until it’s too late. A simple 10-minute test can provide the baseline you need to protect your mobility and strength as you age.
Ready to see where you stand?
