What is a "Bone Density Test?"

Everything You Need to Know About a DEXA Scan

A bone density test, also known as a DEXA scan or DXA, stands for Dual Energy X-Ray Absorptiometry. DEXA scans are the most widely used test to measure bone mineral density.

This measurement reflects the fact that the denser the bone, the less x-rays pass through it.

Usually, the denser your bone, the stronger it is, and the less likely it is to fracture. (Although this isn’t always the case, as we’ll cover a little further down the page!)

If you’ve ever had an x-ray, the process is very similar.

A DEXA machine uses low-energy x-rays and sends two different sources (thus the ‘D’ for “dual” in the name) through the bone in question. The two x-ray sources double the accuracy in measuring your bone density. So, your bone blocks some of the x-rays. And the more dense your bone is, the less x-rays pass through to the detector.

Then, the amount of x-rays passing through the bone is sent to a computer that calculates an average score for the density of your bone.

A DEXA scan is more accurate than a regular x-ray or CAT scan and requires less radiation exposure. More on this in a moment.

But first, let’s go over the different types of DEXA scans!

Types of Bone Density Tests

There are two DEXA scan variations

    1. Central DEXA looks at your whole skeleton, paying special attention to your spine and hips. These machines are usually found in hospitals and medical centers, but some doctors’ offices have them too.
    2. Peripheral DEXA (also called screening tests) are smaller, and focus on your extremities, like your fingers, ankles, and wrists. You often find peripheral DEXA machines in a doctor’s office or smaller medical exam facility. Sometimes, you’ll also see them at health fairs or even bigger shopping malls!

Both Central and Peripheral scans are done on an “outpatient” basis, meaning you aren’t admitted to the hospital to take this test. Central DEXA scans usually take less than 30 minutes, depending on the equipment used and the parts of your body being examined.

In the Central DEXA, you lie comfortably on a padded table. No need to remove your clothes— just make sure there are no zippers that might block the x-rays of your hips and spine. Below the bed is the x-ray generator, and above you is the imaging device.

The person who performs the test will usually place a small pillow to support your legs. This helps your spine lie flat on the table to help get the greatest image. Also, you may find your foot placed in a brace. This keeps your hip nice and still during the procedure. The technician will help you prepare, before walking behind a protective wall. (Remember, the x-ray dose is minimal. But this person takes dozens of x-rays every day, so they need extra protection!)

The imaging detector will pass slowly over your body. During this time you need to hold your breath, but only for a few seconds. Don’t worry, the technician will guide you through it. The scan will produce an image that looks like this:

The Peripheral DEXAs are simpler and only take around 10 minutes. You place your finger, hand, forearm, or foot in a small device that obtains a quick bone density reading.

There is an additional procedure called Lateral Vertebral Assessment (LVA). An LVA is done at many centers. LVA is a low-dose x-ray examination of the spine to screen for vertebral fractures. This test is also performed on the DEXA machine. The LVA test adds only a few minutes to the Central DEXA procedure.

Before your scan, the technician may ask you to complete a quick questionnaire. This helps the doctor determine if you have osteopenia, osteoporosis, or some other medical condition. Your DEXA results reveal your bone mineral density (BMD). Basically, how dense your bones are. The report also lists your T-score and Z-score, which we’ll discuss in more depth in a moment!

Who Should Get a DEXA Scan?

DEXA scans are the best method to diagnose and monitor osteopenia and osteoporosis. The National Osteoporosis Foundation’s guidelines state you should get a DEXA scan if:

    • you are a woman age 65 or older
    • you are a man age 70 or older
    • you break a bone after age 50
    • you are a woman of menopausal age with risk factors
    • you are a postmenopausal woman under age 65 with risk factors
    • you are a man age 50-69 with risk factors

There are numerous factors that can increase your risk of osteoporosis. Below are a few to watch out for. If you say, “That’s me” to two or more items on this list, it may be a good idea to ask your doctor about a DEXA scan!

    • Gender: Women are at higher risk of developing osteoporosis. This is because estrogen decreases sharply during menopause which accelerates bone loss. In fact, in the five to seven years following menopause, a woman can lose up to 20% of her bone density
    • Age: In your lifetime, you increase bone mass from childhood to about your mid-thirties, when you reach your peak bone mass. Then, after age 40, you lose about 1% bone density every year
    • Lack of Exercise: Weight-bearing exercise is one of the best things you can do to strengthen your bones. This type of exercise places stress on your bones, which helps them become stronger. On the other hand, if you don’t exercise, your bones will become weaker over time.
    • Diet: A diet lacking in essential nutrients plays a major role in the development of osteoporosis. As you’re no doubt aware, calcium is crucial for healthy bones. But you also need 12 other minerals and three vitamins to support your bone health! Learn more about diet and nutrition here.
    • Family History: Having a family member with osteoporosis puts you at greater risk because osteoporosis has a strong genetic component.⁴
    • Body Size: Women and men who have small body frames tend to have a higher risk for osteoporosis.⁵

How Does A Bone Density Scan Work?

A DEXA scan involves lying down— generally fully clothed— on a scanning table. A scanning arm painlessly and non-invasively scans your spine, and then your hips, to determine the quantity of bone you have. The results are calculated in a computer, and you’re told your T-score; one of the results of the bone density test.

If your score is -1.0 or above, your bone density is considered normal. If it’s between -1.0 and -2.5, you have osteopenia. If it’s -2.5 or below,, you have osteoporosis. If you’re diagnosed with osteoporosis, don’t worry!

There are things you can do to reverse your bone loss. In fact, several studies suggest that with a healthy lifestyle and the right combination of nutrients, you can increase your bone density. But prevention is the best medicine, so if you have any concerns about your bone health, it’s in your best interest to get a DEXA scan!

Should I Stop Taking My Calcium Supplement Before a DEXA Scan?

Many people worry about whether they should stop taking calcium before a DEXA scan. That’s because they wonder whether the calcium might overstate their DEXA results. But this fear is largely unfounded…

Undissolved calcium could influence your DEXA scan reading— if you take calcium tablets.⁶ Calcium tablets contain binders that can delay dissolution of the tablets in your gut. However, if you take calcium capsules with powder inside like AlgaeCal Plus, this won’t be an issue.

In fact, AlgaeCal arranged a clinical test to observe the dissolution of AlgaeCal raw powder in stomach acid conditions. The test revealed that 96% of the calcium dissolved within 30 minutes. So, if you take AlgaeCal Plus as your calcium supplement, you never have to worry about DEXA scan overstatement.

Okay, but what if you do take calcium tablets?

Even then, taking your calcium supplement before a DEXA scan will have minimal to no effect on your DEXA results. But there are two groups of people who might want to hold off on their calcium for 24 hours before their scan: Those who have poor digestion and those who have poor calcium absorption.

Either group will have trouble absorbing calcium. And that means any unabsorbed calcium can sit in their digestive tract— and be picked up by the DEXA machine. Now, this unabsorbed calcium in the digestive tract could affect the DEXA reading. But if it did, the effects would be minimal!

That said, if you’re in either of these groups, and you’re concerned about DEXA scan overstatement, don’t take supplemental calcium for 24 hours before your scan. Anything longer than 24 hours is unnecessary and could harm your bone health!

Should I Be Concerned About Radiation Exposure?

In short, no! As you can see from the chart below, there’s very little exposure when compared to numerous other types of medical imaging procedures. For perspective, the amount of radiation emitted during a DEXA scan (0.001) is less than you’d be exposed to on a flight from New York to L.A.

If you go back a few decades, the only place to measure your bone health was at a hospital using a full body machine. But to meet the demands of the ever-increasing cases of osteoporosis, more efficient machines to test bone density were invented. Today, thanks to the wonders of technology, DEXA machines can safely, quickly, and painlessly spot a bone density issue on the distant horizon— before a bone fracture alerts you to the problem.

Imaging Procedures and Radiation Doses:⁷

Procedure Average Effective Dose (mSv) Range Reported in the Literature (mSv)

Bone density DEXA


0.00 – 0.035

X-ray, arm or leg


0.0002 – 0.1

X-ray, panoramic dental


0.007 – 0.09

X-ray, chest


0.05 – 0.24

X-ray, abdominal


0.04 – 1.1



0.10 – 0.6

X-ray, lumbar spine


0.5 – 1.8

CT, head


0.9 – 4

CT, cardiac for calcium scoring


1.0 – 12

Nuclear imaging, bone scan



CT, spine


1.5 – 10

CT, pelvis


3.3 – 10

CT, chest


4.0 – 18

CT, abdomen


3.5 – 25

CT, colonoscopy


4.0 – 13.2

CT, angiogram


5.0 – 32

CT, whole body


20 or more

How to Read Your DEXA Scan Results

Even after sitting down with your doctor, you may have follow-up questions or forgotten which numbers meant what! That’s totally normal. And that’s why we’re going to go over your T- and Z-scores (the main numbers shown after your DEXA scan), so you understand exactly what they mean.

Broadly, here’s what your T-scores mean:

  •  -1.0 or above = Your bone density is considered normal
  • Between -1 and -2.5 = Your score is a sign of osteopenia, a condition in which bone density is below normal and may lead to osteoporosis
  • -2.5 or below = Your bone density indicates you have osteoporosis

But let’s dig a little deeper…

What’s My Z-Score and Why Is It Useful?

In technical terms, your Z-score is a measure of the number of standard deviations your bone mineral density is from the average person of your age and gender. An easy way to think about it is that your Z-score helps you see how you’re doing compared to other people in your age range. But when it comes to your overall bone health, there’s a better indication of how you’re doing. Enter the T-Score.

What is a T-Score and What Does it Tell Me?

The T-score is a measure of the number of standard deviations your bone density is from a young adult’s bone density. It basically compares your bone density to someone at peak bone health. Once you reach your peak bone mass around age 40, you begin to lose bone density each year. That’s why comparing your bone density to a young adult’s is more practical because they’re at a lower risk for fractures.

The picture below provides a visual representation of T-scores.

    • The green figures indicate above average BMD; the darker the green, the better your BMD.
    • The yellow figures indicate that you have normal bone density.
    • The orange figures indicate osteopenia (a T-score between -1.0 to -2.5), where bone density is below normal and may lead to osteoporosis.
    • The red figures indicate osteoporosis (-2.5 and below), which is severe bone loss.

For both rows pictured above, the number on the top of each figure is the T-score for bone mineral density (BMD). This will be reported for any bone density test you’ve taken (Left Femur, Right Femur, Spine, or Total Body).

At the bottom of each figure is a “%” score associated with the T-score value. Using a scale of 1 to 100, the “%” score is how your BMD compares to people of your gender in the standard group of “Young Adults” that’s used to diagnose osteopenia and osteoporosis. For example, if your T-score was 0.6, your “%” score would be “73%” suggesting that your BMD was better than 73 out of 100 people of your gender in the comparison group and worse than 27 out of 100!

What’s the Best Way to Measure My Bone Density Progress?

The best way to measure your bone density progress is to track the percentage change in your BMD from your previous DEXA scan. Your T-score is a useful indicator of how your bones compare to someone with peak bone density.

But unfortunately, there isn’t a standard scoring system for T-score values, so they vary from one clinic to the next. What’s more, T-score percentages can be a little broad, so your T-score may not change, even though your bone density increased!

So the percentage change in your BMD is the best indicator of your progress. Remember, BMD stands for bone mineral density— a measure of the mineral content in a certain volume of your bone. So if you see an increase in your BMD, your bones are getting denser and stronger. A BMD decrease means your bones are becoming more porous and weak.

Because different clinics use slightly different equipment and scoring methods, it’s best to have all your DEXA scans at the same clinic. This way, you’ll be able to track your progress accurately.

Note: It’s a good idea to have a DEXA scan before you start a new bone health regimen like AlgaeCal (within 30 days ideally). When you have a recent baseline reading, you can more accurately monitor the impact of the new regimen. If your baseline DEXA scan is older than 30 days, you won’t have an accurate starting point for comparison.

What About My Trabecular Bone Score?

You may have heard of a newer measurement called trabecular bone score (TBS).⁸ The trabecular bone score analyzes the internal texture of your bones, their “micro architecture”. A higher TBS means the internal structure of your bones is stronger, while a lower score means it’s weaker.

So, your TBS tells you about the quality of your bones, and your BMD tells you about their density! And these are the two main factors that contribute to bone strength and reduce fracture risk. That’s why BMD alone isn’t always a reliable predictor of fracture risk. There’s another factor to take into account, and that’s bone quality.

Bones can be mineral-dense, and still be brittle. Basically, you end up with a lot of low-quality bone, that’s still prone to fracture.

So, the real test of a program to increase bone density is whether it also reduces fracture risk. The AlgaeCal studies are a perfect example of the power of increased bone density and quality. In all three studies, not one participant suffered a fracture! That’s zero fractures across a total of 802 participants. So if you’re taking AlgaeCal Plus and Strontium Boost (our Bone Builder Pack), your bone quality is certain to benefit just as your bone density increases.

All this to say, it’s worth asking your medical professional whether you can get your TBS score. Since it’s calculated using your DEXA results, it’s possible to run this test after your scan.

What Can I Do If My DEXA Scan Shows I Have Low Bone Density?

First of all, don’t despair! Of course, a low bone density reading isn’t what anyone wants to receive. But it’s not a done deal. There are things you can do to improve your bone health and even see an increase in your bone density on your next DEXA scan. So, think of a low bone density reading as a wake-up call to incorporate bone-healthy practices into your daily routine!

Here’s some information on changes you can make to improve your bone health:

    • Exercise: Exercise is a crucial aspect of bone health. For more information on the most beneficial forms of exercise for bone health and exercise tutorials, click here to visit our exercises page.
    • Lifestyle Changes: Both dietary and environmental toxins can contribute to bone loss. To discover more about toxins that cause bone loss, and what you can do to limit them, visit this page.
    • Bone-healthy Diet: Fuelling your bones the nutrients they need to stay strong and healthy is incredibly important. And it’s just as essential to avoid the foods that will cause chronic, low-grade inflammation… an underlying cause of bone loss! Find out which foods to include in your diet and which to try to avoid on our diet and nutrition page.
    • Supplementation: Your bones require 13 minerals and 3 vitamins, in particular, to stay strong and healthy. Calcium, magnesium, boron, strontium, zinc, selenium, potassium, phosphorus, copper, nickel, vanadium, silicon, manganese, vitamin C, vitamin D3, and vitamin K2. You could try to plan your grocery shop to include enough foods that contain all of those nutrients. Or you could take 16 separate supplements. Or you could take the only supplement duo that includes all of them, and is clinically supported to increase bone density…

AlgaeCal’s Bone Builder Pack consists of AlgaeCal Plus and Strontium Boost.AlgaeCal Plus is a natural calcium supplement derived from a unique species of marine algae. It contains all the vitamins and minerals your bones need to stay strong, healthy, and fracture-free.

And Strontium Boost supports the bone-building of AlgaeCal Plus by providing a little extra safe and natural strontium citrate.

Clinical studies show that the Bone Builder Pack can increase bone density… in as little as six months!

Remember, it’s never too early to start taking care of your bones! So, if you have any concerns about your bone health, be sure to talk to your doctor about a DEXA scan.

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    Frequently Asked Questions

  • How do you check bone density?
    The only truly accurate way to check your bone density is with a DEXA scan. Regular x-rays will not give you the details (T-score and Z-score) your doctor needs to make an accurate diagnosis.
  • What is the actual name of the bone density test?
    DEXA (or DXA) stands for Dual Energy X-Ray Absorptiometry. There are two types: Central and Peripheral. The first covers your entire skeleton; the second focuses on your extremities, such as your hands or feet.
  • How much does it cost for a bone density test?
    In the US, Medicare covers the cost of your DEXA scan every two years. If you need more scans, please check with your insurance provider for complete coverage details. In Canada, the Federal Government says that if you’re 65 and never had a DEXA, Canadian Medicare will cover it. They’ll also let you do follow-up DEXAs if you need them, every 2 years and cover them. Sometimes, if your treatments are annual, Medicare will cover the cost. What if you’re under 65? Most commercial providers will cover your initial DEXA if you’re post-menopausal and you have risk factors (such as smoking, genetics, or being under- or overweight.) If your health insurance does not cover the cost of your DEXA scan, you will have to pay out of pocket.
  • How often should I have a bone density test?

    Once you reach one of the milestones listed below, you should have a DEXA scan every 2 years:

    • You are a woman 65 or older
    • You are a postmenopausal woman under 65
    • You are a man 70 or older
    • You are 50 or older and recently suffered a bone fracture, especially from a minor fall
  • I have a metal plate/object in my body (head, arm, leg etc.), is it still safe/effective to have a body composition scan?
    Yes. Since the metal object will be present in both initial and future scans, the readings will still be helpful since there is no change in the object. The metal will not greatly affect readings. A DEXA scan’s beams can’t interact with the metal object like an MRI machine’s will, so while the surrounding tissue will be classified incorrectly as bone, readings will still be consistent from scan to scan.



Bone Density Test, Osteoporosis Screening & T-score Interpretation. (n.d.). Retrieved from https://www.nof.org/patients/diagnosis-information/bone-density-examtesting/.


What Women Need to Know. (n.d.). Retrieved from https://www.nof.org/preventing-fractures/general-facts/what-women-need-to-know/#menopause.


Demontiero, O., Vidal, C., & Duque, G. (2012). Aging and bone loss: new insights for the clinician. Therapeutic advances in musculoskeletal disease, 4(2), 61–76. doi:10.1177/1759720X11430858


Stewart, T. L., Ralston, S. H. (2000). Role of genetic factors in the pathogenesis of osteoporosis. J Endocrinol. 166(2), 235e245. doi:10.1677/joe.0.1660235


Osteoporosis. (n.d.). Retrieved from https://www.nia.nih.gov/health/osteoporosis.


Kendler, D. L., Kiebzak, G. M., Ambrose C. G., et al. (2006). Effect of calcium tablets on interpretation of lumbar spine DXA scans. Journal of Clinical Densitometry, 9(1), 97–104. doi:10.1016/j.jocd.2005.12.002


Mettler, F. A., Huda, W., Yoshizumi, T. T., Mahesh, M. (2008). Effective doses in radiology and diagnostic nuclear medicine: a catalog. Radiology 248 (1), 254–263. doi:10.1148/radiol.2481071451


Briot, K. (2013). DXA parameters: beyond bone mineral density. Joint Bone Spine, 80(3), 265–269. doi:10.1016/j.jbspin.2012.09.025