Preparing for a DEXA Scan

A DEXA scan is one of the most accurate and reliable tools we have for measuring body composition.  Only an MRI is more accurate but given the cost, time commitment  and limited availability of MRI, it is impractical to use MRI for routine body composition testing.  

Therefore, a DEXA scan is considered the “practical gold standard” for evaluating body composition and has only 2-3% error when compared to an MRI.  Given this slight amount of error, preparing for a DEXA scan to ensure the most accurate results possible is very important.

Preparing for a DEXA scan: 7 Steps

#1. Perform your DEXA scan first thing in the morning

Performing your DEXA scan first thing in the morning creates a consistent environment each time you scan.  You are able to minimize outside factors and make sure differences are due to real changes in body composition.

#2.  Don’t exercise before your scan 

It is always recommended to avoid exercise for 24 hours prior to your scan.  Exercise creates fluid shifts in the body which can alter results of a DEXA scan.

#3.  Make sure you are hydrated

Make sure you are well hydrated before your scan.  Dehydration can lead to inaccurately low lean mass results on your scan. 

#4. Know your height and don’t overestimate

Most people overestimate their height.  Since pertinent results on your DEXA scan include calculations that take your height into account, it is important to make sure you list your height as accurately as possible.

#5. You should avoid calcium supplements within 24 hours of your scan

If you take a calcium supplement within 24 hours of your scan, it may still be in your intestines and the DEXA will interpret it as dense material.  This can lead to false elevations in bone mineral density results.

#6. You should avoid barium and CT contrast for at least a week before your DEXA scan

Like calcium, barium and iodinated contrast given during a CT scan are radiopaque and may create “artificial” dense areas on the scan, leading to inaccurate bone mineral density results.

#7.  Use the same DEXA scanner each time you scan

Different DEXA machines use slightly different software and calibration, so switching scanners can make it look like your bone density or body fat changed — even if it didn’t. That’s why it’s best to stick with the same machine each time for accurate tracking.  

The Bottom Line

Preparing for a DEXA scan is essential because of small factors — like what you eat, drink, or do before your appointment — can noticeably affect the results. By following the same guidelines each time, you eliminate variables that could throw off your measurements. This consistency ensures that your scan accurately reflects real changes in your bone density or body composition, allowing you and your doctor to track your progress with confidence.