Sensitivity and Specificity of Sub-Epidermal Moisture (SEM) assessment in detecting localised oedema in an ex vivo porcine model

BACKGROUND: Current studies examining the sensitivity and specificity of sub-epidermal moisture (SEM) assessment for pressure injury (PI) detection have relied on visible skin changes and clinical judgement as a standard comparator. This approach underestimates the diagnostic accuracy of SEM assessments in detecting localised oedema, which precedes and predicts later stages of pressure-induced tissue death. To address this limitation, a porcine skin model was developed to validate the performance of SEM assessments in detecting developing pressure-induced injuries. METHODOLOGY: Localised oedema was induced into the hind limbs of an ex vivo porcine model via controlled intradermal injections. Two SEM readings were taken from the injection site and two from a control site positioned away from the injection area, resulting in four raw SEM readings. The SEM delta (Δ) value was then calculated in increments of 1 mL of saline injected (10x each). True/false positive and true/false negative rates were evaluated and analysed by correlating the presence of induced localised oedema with SEM Δ values ≥ 0.6. Results are reported as sensitivity and specificity. RESULTS: A total of 200 SEM Δ values were collected. Data analysis yielded a sensitivity of 93% and a specificity of 96% in detecting localised oedema in the soft tissue of a porcine model. CONCLUSION: The porcine model used in this study simulates localised oedema volume representative of the earliest stages of PI development in humans. SEM assessment technology was able to detect these changes with high accuracy, demonstrating >90% sensitivity and specificity. Thus, SEM assessment represents a promising validated tool for detecting localised oedema, an indicator of developing tissue damage which is consequential for daily PI prevention and care practices.