Evaluating the sensitivity, specificity and clinical utility of algorithms of spatial variation in sub-epidermal moisture (SEM) for the diagnosis of deep and early-stage pressure-induced tissue damage

J Wound Care. 2021 Jan 2;30(1):41-53. doi: 10.12968/jowc.2021.30.1.41.


Background: Sub-epidermal moisture (SEM) is a measurable biomarker detecting early pressure damage in order to objectively support current 'gold standard' skin tissue assessments (STA) for the detection of deep and early-stage pressure-induced injuries or ulcers (PI/PUs).

Objective: A multi-site, dual arm, cross sectional, retrospective study was conducted to evaluate the sensitivity, specificity and clinical utility of spatial variation in SEM readings between healthy and damaged skin tissue.

Method: The study enrolled 175 subjects: 125 with confirmed PI/PUs or suspected deep tissue injury (sDTI), and 50 confirmed healthy subjects. Expert principal investigators and PI/PU healthcare practitioners (HCPs) evaluating all subjects were trained in SEM measurements but blinded to clinical interpretation of SEM readings. Sequential and spatial SEM readings of the sacrum and heels, subjects' demographic data, STAs, risk assessment tool scores (RATS), pain assessment and potential confounders were recorded. Independent statistical analyses were performed.

Results: Mean spatial SEM measures within subjects with healthy tissue and within subjects with damaged tissue were statistically similar. Mean spatial SEM measures within anatomies of subjects with damaged tissue were significantly different (p<0.05). There was no significant difference between spatial readings in healthy subjects. Algorithms computing a range of SEM delta thresholds indicated a sensitivity of 82-87% and a specificity of 51-88% at an SEM delta ≥0.6. Receiver operating characteristic (ROC) curves computed areas under the curve (AUC) of 0.7809-0.9181 (95% CI: 0.7221-0.8817, 0.8397-0.9545, p<0.0001) exceeding clinical judgement.

Conclusion: These SEM data augment clinical decision-making for developing intact skin PI/PUs including sDTIs and Stage I PI/PUs. Informing HCPs of this subclinical, non-visible skin and tissue damage and providing opportunities for alternative PI/PU care pathways is an exciting prospect.

Keywords: diagnostic accuracy; pressure injury; pressure ulcer; risk assessment; skin tissue assessment; sub-epidermal moisture; ulcer; wound.

Publication types

  • Evaluation Study

MeSH terms

  • Adult
  • Algorithms*
  • Cross-Sectional Studies
  • Epidermis / physiology*
  • Female
  • Humans
  • Male
  • Middle Aged
  • Predictive Value of Tests
  • Pressure Ulcer / diagnosis*
  • Retrospective Studies
  • Risk Assessment
  • Severity of Illness Index