A DXA report is a stack of numbers that only compare across visits if the scanner, software and positioning stay the same. This eCRF records the scan conditions with the results, so a change in lean mass means a change in the participant.
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Scan conditions
Scan date
DXDTCFasted at least 4 hours
Software version
DXSWVResults
Total lean mass
LEANTOTAppendicular lean mass
ALMALMI derived in analysis
Total fat mass
FATTOTDXA data capture at a glance
The method
DXA passes two X-ray energies through the body and infers the proportion of bone mineral, fat and lean soft tissue from how each is attenuated. It is the reference method in most nutrition, longevity, metabolic and musculoskeletal trials because it is fast, low in radiation exposure compared with other imaging and precise enough to track change. Its lean mass figure is not muscle alone: it includes water, organs and connective tissue, which is why hydration and recent exercise or food intake can move it.
A longevity or muscle-preservation trial often has lean mass or ALMI as a primary or key secondary endpoint, which makes the capture form a data-quality tool as much as a data-entry one. If the baseline scan used one software version and the week 24 scan another, or the participant was positioned differently, the difference can be larger than the treatment effect. A good form therefore captures the conditions next to the results and lets monitors check them. For the wider setup of ageing studies, see EDC for longevity clinical trials and how to run a longevity clinical trial.
ALMI is ALM (arm plus leg lean mass) in kilograms divided by height in metres squared. EWGSOP2 lists ALM/height2 below 7.0 kg/m2 in men and below 5.5 kg/m2 in women as low muscle mass. The FNIH project used ALM adjusted for BMI instead, so state which definition your protocol follows. Fat mass index and fat-free mass index follow the same height-squared logic. Body mass index itself is one of Capture's calculated fields on the vital signs form, so height and weight on that form can feed your DXA analysis.
Field by field
| Field | Type | Notes |
|---|---|---|
| Scan date and time | Date, time | Needed to link to the visit and to the pre-scan fasting window |
| Scanner make and model | Dropdown or text | Fixed per site; changes need a protocol note |
| Scan mode and software version | Text | Same version at every visit; flag any upgrade |
| Participant height and weight on the day | Number | Measured at the scan, not carried over from screening |
| Fasting and recent exercise | Single choice | Fasting hours and strenuous exercise in the last 24 hours, per your protocol |
| Positioning acceptable | Single choice | Yes, or no with reason (movement, clothing, artefact, body size beyond the table) |
| Total mass, fat mass, lean mass | Number, kg | Whole-body totals from the report |
| Body fat percentage | Number, % | As printed by the software |
| Arm and leg lean mass (left, right) | Number, kg | Sum to ALM in analysis, or enter ALM from the report |
| Bone mineral content and density | Number, g and g/cm2 | Whole body and, if required, lumbar spine and hip |
| T-score and Z-score | Number | Only where the protocol needs them; reference database noted |
| Visceral adipose tissue | Number | Unit and estimation method named; vendor-specific |
| Scan quality and operator | Single choice, text | Operator initials support site-level quality review |
| Report file reference | Text | Pointer to the source report kept at site for monitoring |
The lists above are a starting point. Match field names to your protocol and the scanner report your sites actually print.
Build it in Capture
Build the form as a standard eCRF and place it on the visits where DXA is scheduled. The site enters the values from the printed report during or right after the visit.
Edit checks / auto-queries
2Type
Range High
Operator
Greater than
Value
180
Priority: High
Type
Range Low
Operator
Less than
Value
80
Priority: Normal
Query raised automatically
Value 192 violates limit (180). Please verify.
Setup
Add the scan-condition section first, then results grouped as whole body, regions and bone. Number fields carry the unit in the label.
Choose plausible low and high limits from your population (for example adult whole-body lean mass in kilograms) and set them as edit checks. Test with an extreme value in the sandbox to see the auto-query.
Use custom-value rules to compare software version with the baseline value and to require a reason when positioning is not acceptable.
Mark the endpoint fields for source data verification so the report is checked against what was entered.
Approve the form (approved forms are locked for live use) and add it to the baseline and follow-up visits.
Write ALMI, fat mass index and any BMI-adjusted definitions into the statistical analysis plan. They are computed from the export, not in the form.
Worked example
Demo data for one participant: height 1.72 m, appendicular lean mass 20.4 kg at baseline and 21.9 kg at week 24. ALMI is 20.4 / 1.72 squared, which is 6.9 kg/m2 at baseline, and 21.9 / 1.72 squared, which is 7.4 kg/m2 at week 24. In a male participant that moves from just under the EWGSOP2 low-muscle-mass cut-off of 7.0 to above it. Before reading that as a treatment effect, the analyst checks the metadata the form captured: same scanner, same software version, fasted at both visits, positioning acceptable. If any differs, the change is annotated or the scan queried.
This is the reason the form is not just a place to type the report. The metadata fields cost seconds to complete and make the difference between a number and an interpretable number.
Week 24 ALMI, kg/m2
7.4 / 10
Before go-live
Follow-up scans on the same device, with calibration and quality-control scans logged at site.
Any upgrade mid-study is documented, and cross-calibration data are kept if scans move to a new version.
Fasting window, exercise restriction and clothing are written in the protocol and recorded on the form.
Positioning and region-of-interest placement follow the manufacturer's guidance and a site SOP.
ALMI, fat mass index, visceral fat method and any reference database are named in advance.
The protocol says what the site does if a scan shows something unexpected, and where that is recorded, for example the adverse event form.
Build the fields, set the edit checks and enter a scan in the free sandbox. No credit card.
Scanner model, software version, scan mode, operator, fasting and exercise status, participant height and weight on the day, and whether positioning was acceptable. These explain differences between visits that are not biological.
No. Capture's built-in calculated fields are a fixed set of clinical derivations such as BMI, BSA and eGFR. Store ALM, fat mass and height, and derive ALMI and fat mass index in your analysis program from the export.
Site staff, from the printed scanner report. It is a site-completed eCRF, not a participant questionnaire.
DXA is a measurement method, not a copyrighted questionnaire, so there is no instrument licence to record. Scanner software and reference databases have their own vendor terms, which stay with your site agreements.
Not safely. Visceral fat estimates are software features of some scanners and methods differ. Record the method and keep one scanner type within a study.
Yes. Add lumbar spine and hip regions, BMC, BMD, and T-score or Z-score fields with the reference database named. The structure is the same.
Capture exports SDTM datasets as SAS XPT files with Define-XML. Each template carries an OID and an SDTM domain, so confirm the mapping for your body composition variables in the Define-XML review.
Keep exploring
Build the form, set the checks and test an entry. Free sandbox, no credit card.