CARROtS Collaborative
Protocol & Best Practices
Standardized methods for using the Veggie Meter® in research — covering device setup, measurement procedures, analysis, and reporting.
Note from the collaborative: These are the details we decided speakers should share in their presentations and that researchers should report in publications. We are not stating that our methods are the "right" way — we are intentionally working toward greater consistency and transparency across studies. Consider and highlight any differences between your methods and the protocol paper.
Foundational protocol paper
Radtke MD et al. Recommendations for the Use of the Veggie Meter® for Spectroscopy-Based Skin Carotenoid Measurements in the Research Setting. Curr Dev Nutr. 2021.
Device & Setup
Veggie Meter® year, model, and calibration
Proper setup and calibration are essential for producing reliable skin carotenoid scores. Always report which device you used and how it was calibrated.
Report your device year & model number
Identify and record the specific year and model of the Veggie Meter® used. This is critical for comparability across studies, as device specifications may vary across versions.
Calibration procedure
Calibrate using the dark and white reference blanks before performing measurements. Recalibrate every hour of continuous use, or any time the device is moved to a new location. If calibration graphs do not match reference images, repeat the calibration.
Environmental conditions
The Veggie Meter® is sensitive to heat, cold, and bright light. Allow 15 minutes for the device to acclimate when introduced to a new environment with substantial changes in temperature or lighting.
Multiple devices
If using more than one Veggie Meter®, always record which device was used for each participant. Interdevice variability is a known source of error that must be documented and accounted for in analysis.
Measurement Procedure
Finger selection, preparation, and scan mode
Consistent measurement procedures reduce within- and between-study variability. At minimum, report the finger used, site preparation method, and scan mode for every study.
1
Participant preparation
Describe the measurement procedure to participants before beginning to avoid apprehension. When working with children or toddlers, verbally explain and demonstrate the process. Have participants wash hands with soap and warm water before measurement. If handwashing is unavailable, use a premoistened alcohol prep pad. Hand sanitizer is not recommended as it may not remove pigment or debris.
2
Finger & hand selection
The standardized protocol recommends the nondominant ring finger. The nondominant hand minimizes oxyhemoglobin and deoxyhemoglobin interference from increased vasculature in the dominant hand. The ring finger is preferred over the index finger due to decreased callusing, which allows greater light penetration. Always report which finger you used, regardless of whether you follow the standard recommendation.
3
Scan mode
Report which scan mode was used. Options include: (a) single scan, (b) triplicate scan that produces a single averaged score ("Average of 3 Scans" mode), (c) multiple individual scans averaged manually, or (d) another approach. Triplicate measurements are recommended for research purposes to account for tissue inhomogeneities and increase reproducibility. The digit should be retracted between measurements to allow reperfusion.
4
Error handling
If the device returns an error or a score of 0, confirm the finger has no contaminants, reposition the finger in the center of the contact lens, and repeat the measurement. If the error persists, document the attempt. It is not recommended to switch to a different finger to obtain a score, as this affects reproducibility.
5
Sharing results with participants
Decide in advance whether to share scores with participants, based on study design. For intervention studies aimed at increasing scores over time, blinding participants is recommended to prevent behavior change. If sharing scores, emphasize that results cannot be compared between individuals at this time and that a low score does not equate with poor health.
Analysis
Recommended analytical approaches
Additional information coming soon.
Reporting & Common Language
How to describe the Veggie Meter® in your work
Additional information coming soon.
Grantmanship
Writing the Veggie Meter® into grants
Additional information coming soon.
Recruitment Materials
Sample materials for participant recruitment
Additional information coming soon.
Have protocol guidance to contribute?
The collaborative is always refining these recommendations. Share your experience or suggested additions via the website survey.
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