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# Understanding Forearm DEXA Results and What They Mean for Bone Health
- URL: https://blog.groovehealth.com/understanding-forearm-dexa-results-and-what-they-mean-for-bone-health/
- Published: 2026-11-02T02:10:15.000Z
- Updated: 2026-11-02T08:58:54.000Z
- Description: A forearm DEXA scan measures the 33% radius, the one forearm site used to diagnose osteoporosis when hip or spine scans can't be read. Here is how to interpret the T-score, Z-score and your report.
- Author: Groove Editorial Team
- Tags: DXA Scan, Bone Density, Osteoporosis, Fracture Risk

## What Forearm DEXA Results Tell You

Understanding your forearm DEXA results starts with understanding the **one-third (33%) radius** score. This is the forearm measurement used to classify bone density in postmenopausal women and men age 50 and older. A low T-score at this site may support an osteoporosis diagnosis, especially when hip or spine scans cannot be measured or interpreted.

A few items to look for on your report:

1. **Which region was measured:** Look for "33% radius" or "one-third radius."
2. **Which score applies to you:** T-scores are generally used for older adults; Z-scores compare bone density with people of the same age and sex.
3. **Why your forearm was scanned:** It is often used when spine or hip results are unclear, or when a condition such as primary hyperparathyroidism may affect the hard outer layer of bone.

Forearm results can differ from spine and hip results. That does not automatically mean one scan is wrong. Each site contains different mixes of bone and can be affected by different health conditions or scan artifacts. For broader context, see our guide on [how to read a DEXA scan report](https://blog.groovehealth.com/how-to-read-a-dexa-scan-report/).

## Clinical Indications: Why and When Doctors Scan the Forearm

Doctors order a forearm DEXA scan when standard central sites like the hip or spine cannot be measured, when body weight exceeds table limits, or when evaluating suspected primary hyperparathyroidism. Under [medically necessary bone mass measurement guidelines](https://www.medicare.gov/coverage/bone-mass-measurements?ref=blog.groovehealth.com), scanning this peripheral site gives clinicians a reliable alternative to assess skeletal strength and break risk.

A dual-energy X-ray absorptiometry (DEXA) scan uses low-dose X-rays to measure how strong bones are. While the lower back (lumbar spine) and hips are the standard places to scan, physical limitations often prevent accurate readings at these central sites. Severe scoliosis, advanced spinal arthritis, or previous surgeries can distort central readings. In these situations, the forearm serves as an approved, valid testing site.

Forearm scanning also solves practical equipment challenges. Standard DEXA tables have specific weight thresholds. When an individual exceeds these limits, a forearm scan can be completed while the person sits comfortably beside the machine. It is also an excellent option for adults with severe curvature of the spine (kyphosis) or severe shortness of breath when lying flat (orthopnea).

![Flowchart of clinical indications for forearm DEXA scanning](https://storage.googleapis.com/ai-templates.appspot.com/temp_images/83cc06239b3546538afafeb39399eb1e.png "Flowchart of clinical indications for forearm DEXA scanning")

### When Hip and Spine Scans Cannot Be Interpreted

When central sites cannot be interpreted, the forearm provides the data needed to evaluate baseline bone health. Bilateral hip replacements, metal pins, spinal fusion rods, and compression fractures add artificial density to central images. This extra density falsely elevates T-scores and masks underlying bone thinning.

In such cases, imaging the forearm bypasses these local distortions. The forearm scan gives your healthcare provider an uncompromised view of cortical bone mineral levels, ensuring that thinning bones are not overlooked simply because central joints have undergone surgical repair.

### Primary Hyperparathyroidism and Cortical Bone Loss

Primary hyperparathyroidism is a hormonal disorder that directly targets the forearm. In this condition, overactive parathyroid glands produce too much parathyroid hormone. This excess hormone pulls calcium directly out of the hard outer layer of bone, known as cortical bone.

Because the shaft of the radius bone in the forearm consists almost entirely of cortical bone, it shows bone loss much earlier and more severely than the spine. According to the [International Society for Clinical Densitometry's adult official positions](https://iscd.org/official-positions-2023/?ref=blog.groovehealth.com), including a forearm scan is a standard recommendation when managing hyperparathyroidism. Gaining a clear perspective on [understanding osteoporosis](https://blog.groovehealth.com/understanding-osteoporosis/) related to hormonal imbalances ensures patients receive appropriate medical evaluation.

## Anatomy and Measurement Regions: 33% Radius vs. Ultradistal

The forearm consists of two long bones: the radius, located on the thumb side, and the ulna, located on the pinky side. During a forearm bone density test, software evaluates the space between these bones and divides the radius into distinct regions of interest.

![Forearm DEXA scan regions of interest showing radius anatomy](https://images.bannerbear.com/direct/4mGpW3zwpg0ZK0AxQw/requests/000/164/035/424/DqR2v1kNaYMDLK1jQ8epZrOWP/b3f73e6d672a2af860913fb47345c39664634ca2.jpg "Forearm DEXA scan regions of interest showing radius anatomy")

These separate regions contain entirely different structures of bone tissue:

- **One-Third (33%) Radius:** Located along the mid-to-upper shaft, this area is over 95% dense cortical bone.
- **Mid-Radius:** Situated between the shaft and the wrist, containing a moderate blend of cortical and spongy bone.
- **Ultradistal (UD) Radius:** Positioned right next to the wrist joint, this region is rich in porous, spongy trabecular bone.

### Anatomical Landmarks and Selection Rules

Technicians identify the correct scan area by measuring forearm length from the ulnar styloid process (the bony bump on the outside of the wrist) to the olecranon process (the tip of the elbow). This precise length measurement ensures that software places the region of interest boxes in the exact anatomical positions.

By clinical convention, technicians scan the non-dominant arm. The arm you use for writing, carrying groceries, and daily chores experiences constant mechanical loading. This regular muscle pull increases bone mass on the dominant side. Scanning the non-dominant arm avoids this activity-related boost and provides a conservative estimate of skeletal break risk.

However, technicians will scan the dominant arm if the non-dominant arm has specific issues, including:

- A prior wrist break or forearm fracture
- Retained surgical plates, screws, or pins
- A dialysis arteriovenous (AV) fistula
- Severe lymphedema or swelling
- Marked contractures or paralysis

During the scan, the hand is placed flat with the palm facing down **without twisting too far.** Pronation simply means turning the forearm so the palm faces downward. If the arm rotates too much, the radius can cross over the ulna, creating an overlap artifact that prevents the software from accurately measuring the separate bones.

### Why Only the One-Third Radius Is Used for Diagnosis

Although your report may list several numbers, clinical guidelines from the [International Society for Clinical Densitometry](https://iscd.org/official-positions-2023/?cn-reloaded=1&ref=blog.groovehealth.com) state that only the **one-third (33%) radius** can be used to formally diagnose osteopenia or osteoporosis.

| Forearm Region                   | Primary Bone Type                                | Clinical Function on DEXA Report                  | Diagnostic Validity                               |
| -------------------------------- | ------------------------------------------------ | ------------------------------------------------- | ------------------------------------------------- |
| **33% (One-Third) Radius**       | Mostly cortical bone, often about 95%            | Main forearm site used for T-score classification | **Yes, when forearm DXA is clinically indicated** |
| **Mid-Radius**                   | Mixed, but mainly cortical bone                  | Supplemental regional measurement                 | No, not used for WHO diagnostic classification    |
| **Ultradistal (UD) Radius**      | Trabecular-rich bone near the wrist joint        | Descriptive measure of wrist-area bone density    | No, not used for WHO diagnostic classification    |
| **Total Forearm / Total Radius** | Combined average across measured forearm regions | Summary measurement for the scanned forearm       | No, not used for WHO diagnostic classification    |

The ultradistal and total forearm scores are helpful descriptive markers for research and specialized evaluation, but they have higher measurement variation. Learning [how to interpret bone density](https://blog.groovehealth.com/how-interpret-bone-density/) properly requires focusing on the 33% radius row in your report.

## Interpreting T-Scores and Z-Scores on a Forearm Scan

Forearm DEXA reports present two primary statistical comparisons: T-scores and Z-scores. These scores express how many standard deviations your bone mineral levels fall above or below a designated reference population.

Reviewing [what T-scores and Z-scores mean in DEXA scans](https://blog.groovehealth.com/what-does-t-score-and-z-score-mean-in-dexa-scans/) clarifies which number applies to your specific demographic group.

### How to Read T-Scores and Diagnose Osteoporosis

For postmenopausal women and men aged 50 and older, the T-score is the gold standard diagnostic metric. It compares your bone strength to the average peak bone mass of a healthy young adult.

The World Health Organization (WHO) defines these diagnostic categories:

- **Normal Bone Density:** T-score of -1.0 or higher
- **Osteopenia (Low Bone Mass):** T-score between -1.0 and -2.5
- **Osteoporosis:** T-score of -2.5 or lower

A T-score at or below the -2.5 threshold at the one-third radius can establish a standalone diagnosis of osteoporosis if hip and spine readings are unobtainable. If your report shows a [T-score below -2.5](https://blog.groovehealth.com/t-score-below-25-meaning/), your healthcare provider will interpret this as a sign of significant skeletal fragility.

### What a Low Z-Score Reveals About Secondary Causes

A Z-score compares your bone mass to an average group of healthy individuals of the same age, biological sex, and body size. In adults age 65 and older, Z-scores are primarily used to spot unexpected, accelerated bone loss that exceeds normal age-related declines.

A Z-score of -2.0 or lower is defined as "below the expected range for age." When a forearm scan yields an unusually low Z-score, clinicians typically investigate secondary causes of bone loss. These may include malabsorption disorders, chronic kidney issues, vitamin D deficiency, or the long-term use of steroid medications.

## Why Forearm Results Differ from Spine and Hip Scores

It is common for a forearm T-score to disagree with numbers from your hip or spine. This clinical phenomenon is called T-score discordance.

![Comparison of dense cortical bone and porous trabecular bone](https://images.bannerbear.com/direct/4mGpW3zwpg0ZK0AxQw/requests/000/164/035/414/0eb715rd3zLm0Vnk6BPpEmKay/fd594ed515ee0b4876b0af7ff05292d479664938.jpg "Comparison of dense cortical bone and porous trabecular bone")

**Discordance** happens because the skeleton is not uniform throughout the body. Different bones have distinct jobs, experience different mechanical forces, and remodel at entirely different speeds. Furthermore, spinal osteoarthritis and disc degeneration frequently deposit extra calcium spurs (osteophytes) onto vertebral joints. This artificial calcification makes the spine look deceptively dense on a 2D X-ray, while the forearm remains free from these weight-bearing spinal artifacts.

### Cortical Versus Trabecular Bone Composition

The human body contains two structural types of bone:

1. **Cortical Bone:** The hard, compact outer shell found in the shafts of long bones, such as the 33% radius. It remodels slowly and provides rigid structural defense.
2. **Trabecular Bone:** The spongy, honeycomb-like inner network found in high concentrations inside the vertebral bodies of the spine and the ends of the hip. It has high metabolic activity and remodels rapidly.

Estrogen is a natural hormone that helps protect bone strength by slowing the breakdown of bone tissue. During early menopause, a drop in estrogen causes the body to break down bone faster than it can rebuild it, primarily affecting spongy trabecular bone. As a result, spinal T-scores may drop sharply while the cortical one-third radius remains stable. A normal forearm reading does not rule out spinal fragility. For comprehensive education on how bone architecture changes, explore patient resources from the Bone Health and Osteoporosis Foundation.

### Fracture Risk Assessment and FRAX

Fracture risk assessment tools, such as the WHO-developed FRAX calculator, calculate an individual's 10-year probability of experiencing a major osteoporotic break. Standard FRAX algorithms specifically require femoral neck bone density inputs and cannot directly substitute forearm scores into the calculator.

Even so, a low 33% radius score remains a strong independent indicator of systemic break risk. When hip data is missing, clinicians use the forearm T-score to gauge general skeletal fragility. Discover how these clinical scores translate into everyday safety by reading about [DEXA T-score fracture risk correlation](https://blog.groovehealth.com/dexa-t-score-fracture-risk/).

### How to Prepare and What to Expect During the Scan

Preparing for a forearm scan requires minimal effort, but attention to a few key details ensures pristine image quality:

- **Clothing:** Wear loose, comfortable clothing with short sleeves or sleeves that roll up easily. Avoid shirts with metal zippers, snaps, or metallic threads near the wrist.
- **Jewelry:** Remove all watches, fitness trackers, bracelets, and rings before the scan begins.
- **Supplements:** Avoid taking calcium supplements for 24 hours prior to the test to prevent unabsorbed tablets from interfering with imaging fields.
- **During the Test:** You will sit still with your forearm secured in a positioning strap to prevent involuntary twitches. The scanner arm slowly moves over your wrist and lower arm for about two to five minutes.

### Why the Forearm Is a Poor Monitoring Site

While the forearm is an outstanding tool for initial diagnosis, medical guidelines caution against using it to monitor routine treatment progress over short time spans.

Because the one-third radius is composed almost entirely of dense cortical bone, its natural remodeling rate is very slow. When patients start bone-strengthening medications, positive mineral changes show up first in the trabecular-rich spine and hip. Forearm cortical bone changes very little over one to two years of therapy.

Because typical yearly changes at the forearm fall within the scanner's margin of error (least significant change), serial forearm scans rarely demonstrate meaningful treatment response over brief intervals.

## Frequently Asked Questions About Forearm Bone Density

### Can a forearm DEXA scan alone diagnose osteoporosis?

Yes. According to clinical standards from the ISCD, an osteoporosis diagnosis can be established using a T-score of -2.5 or lower at the 33% (one-third) radius of the non-dominant forearm when hip or spine sites cannot be evaluated.

### Why was my non-dominant arm scanned instead of my dominant arm?

The non-dominant arm is scanned by standard protocol because habitual use and muscle loading make the dominant arm slightly denser. Scanning the non-dominant arm prevents overestimating bone strength and ensures an accurate, conservative assessment of break risk.

### Can I use forearm bone density to track treatment progress?

Generally, no. The diagnostic 33% radius consists of slow-remodeling cortical bone. Most bone-building and bone-preserving medications take several years to show measurable mineral changes in the forearm, making the spine and hip superior sites for tracking therapy.

## Putting Your Forearm DEXA Results Into Action

Forearm DEXA scans provide essential clinical insights into your bone health, particularly when central hip and spine scans are obstructed by surgical hardware, severe arthritis, or positioning limitations. By focusing on the 33% radius measurement, you and your doctor can accurately identify low bone mass, uncover potential secondary causes like primary hyperparathyroidism, and take early action to reduce the chance of breaks.

Once you understand your scan results, adopting a structured, home-based exercise plan designed with medical and physical therapy guidance can help strengthen bone, improve stability, and protect against fractures. [Groove Health](https://www.groovehealth.com/?ref=blog.groovehealth.com) is a Medicare covered bone health program for adults 65 and older that pairs each member with a physician and a physical therapist who designs a personalized exercise plan. Working with your healthcare team to review your complete medical history alongside your scan numbers ensures a well-rounded approach to long-term mobility.

For more guidance on navigating your full scan report, read our guide on [interpreting DEXA scan results](https://blog.groovehealth.com/interpreting-dexa-scan-results/).

This content is for informational purposes only and does not constitute medical advice. Consult a qualified healthcare professional for diagnosis and treatment. If you are on Medicare and interested in a personalized bone health program, you can check your eligibility at groovehealth.com.

## Works Cited

1. International Society for Clinical Densitometry. “[Official Adult Positions](https://iscd.org/official-positions-2023/?ref=blog.groovehealth.com).” ISCD, 2023.
2. Centers for Medicare & Medicaid Services. “[Bone Mass Measurements](https://www.medicare.gov/coverage/bone-mass-measurements?ref=blog.groovehealth.com).” Medicare.gov, accessed 2026.
3. World Health Organization Study Group. “[Assessment of Fracture Risk and Its Application to Screening for Postmenopausal Osteoporosis](https://pubmed.ncbi.nlm.nih.gov/7941614/?ref=blog.groovehealth.com).” *World Health Organization Technical Report Series*, no. 843, 1994.