Real Surface Area and Percentage Area Reduction (PAR)

Parable features two imaging modes capable of automatically calculating the real surface area of wounds, in addition to length, width, depth, and volume. Automatic measurements support clinicians in tracking wound progression with objective data that is reproducible over time, enabling meaningful comparisons across visits.

Smart Photo 2.0 features a 'sensor-less' scanning process that automatically calculates length, width, and real surface area.

3D Smart Scan captures full three-dimensional topographical data, automatically calculating wound length, width, depth, surface area, and volume.  

PAR in Wound Healing Evaluation

Percentage Area Reduction (PAR) is a key indicator in wound healing and refers to the change in wound surface area over a defined period. Clinically, PAR provides a precise, quantitative foundation for evaluating wound healing trends.

The predictive validity of PAR was established more than two decades ago by Sheehan et al., who demonstrated that a 50% reduction in wound area after 4 weeks (4-week PAR) was a strong predictor of complete healing by 12 weeks in diabetic foot ulcers.¹

More recently, a comprehensive review of 17 clinical trials confirmed PAR’s role as a surrogate endpoint for wound healing, with PAR seeing use across diverse study designs.² A post hoc analysis of a large multicenter randomized trial further validated the prognostic value of 4-week PAR, reaffirming findings from earlier research.³

Real Surface Area Measurement

Standard ruler-based measurements of wounds not only require direct tissue contact, but have been shown to inaccurately overestimate wound area by up to 40%.^4,5 

Parable's 2D and 3D scans allow you to define the true wound boundary and measure only the wound tissue, proving a 'real' and far more accurate surface area measurement. In the example below, showing results from a Parable 3D Scan, the real measured surface area outlined in blue (71.9cm²) is significantly lower than a length by width calculation would produce (10.9 x 10.4 = 113.3cm²).

Accurate surface area measurements provide the best insight into wound progression across a variety of wound types. In pressure injuries, baseline wound size is a significant predictor for healing at 4 weeks;⁶ since length and width alone may not account for significant changes in size, the real surface area measurement is even more important for high-risk wounds. 4-week PAR was also used to evaluate foot ulcers in a study of 704 diabetic patients, which found that wounds with less than 50% surface area reduction in 4 weeks are less likely to heal.⁷ 

Parable's Non-Healing Wound Report provides insight into wound progression based on the 4-week PAR.  

References

1. Sheehan P, Jones P, Caselli A, Giurini JM, Veves A. Percent change in wound area of diabetic foot ulcers over a 4-week period is a robust predictor of complete healing in a 12-week prospective trial. Diabetes Care. 2003;26(6):1879-1882.
2. Serena T, Yaakov S, Yaakov R, King E, Driver VR. Percentage area reduction at week 4 as a prognostic indicator of complete healing in patients treated with standard of care: a post hoc analysis. J Wound Care. 2024;33(Sup9):S36-S42. doi:10.12968/jowc.2024.0141
3. Lammert A, Kiehlmeier S, Dissemond J, Munter KC, Schnorpfeil W, Pohl J. Percentage area reduction as surrogate for complete healing of hard-to-heal wounds: a review of clinical trials. J Wound Care. 2024;33(10):737-755. doi:10.12968/jowc.2023.0117
4. Jørgensen LB, Sørensen JA, Jemec GB, Yderstræde KB. Methods to assess area and volume of wounds – a systematic review. Int Wound J. 2015;13(4):540-553. doi:10.1111/iwj.12472
5. Rogers LC, Bevilacqua NJ, Armstrong DG, Andros G. Digital planimetry results in more accurate wound measurements: a comparison to standard ruler measurements. J Diabetes Sci Technol. 2010;4(4):799-802. doi:10.1177/193229681000400405
6. Guihan, Marylou et al. Difficulty in Identifying Factors Responsible for Pressure Ulcer Healing in Veterans With Spinal Cord Injury. Archives of physical medicine and rehabilitation vol. 97,12 (2016): 2085-2094.e1. doi:10.1016/j.apmr.2016.05.025
7. Coerper, Stephan et al. Fifty percent area reduction after 4 weeks of treatment is a reliable indicator for healing--analysis of a single-center cohort of 704 diabetic patients. Journal of diabetes and its complications vol. 23,1 (2009): 49-53. doi:10.1016/j.jdiacomp.2008.02.001