Evaluation of Novel Sub-Epidermal Moisture (SEM) Technology in Early Pressure Ulcer Detection Versus Conventional Techniques

Sharon O’Keeffe Wound C.N.S. & Ms Pat McClusky A.N.P. Wound Management
Abstract submitted and accepted to the Tissue Viability Society, 2019

Background and Objectives

Hospital Acquired Pressure Ulcers (HAPUs) remain a challenge and, despite intensive and varied practices for predicting and preventing pressure ulcers (PU), diagnosis is typically based upon subjective visual skin assessment (VSA). Unfortunately, such qualitative methods can be unreliable and may delay both the diagnosis and implementation of preventative measures.

Sub-Epidermal Moisture (SEM)

Advanced near-patient diagnostic techniques exploit the discovery that increasing levels of SEM may be indicative of tissue inflammation, oedema and impending PU.1, 2

As a measurable biophysical marker, even small differences in SEM within adjacent anatomical locations can be quantified, compared and recorded over time, using non-invasive technology. The results alert clinicians to nascent tissue damage, often before redness (erythema) is visible; this enables the timely deployment of preventative interventions.1, 3

Quantitative measurement

SEM levels are measured during routine skin inspection using a hand-held scanner device. Multiple readings are taken over high-risk anatomical locations (target) and the adjacent skin (control) (fig. 2). If the difference in sub-epidermal moisture levels (SEM Δ ) are ≥0.6 a positive result is recorded, suggestive of imminent tissue damage. If a second positive reading is obtained within 48 hours, a diagnosis of Category 1 PU3 is confirmed.


To compare the clinical utility of using a SEM scanning device versus subjective visual skin inspection in the early detection of Category 1 PU.3


  • To observe whether SEM data triggers the allocation of preventative interventions
  • To compare the rate of hospital-acquired pressure ulcers (HAPU) before and during the SEM scanner evaluation

Figure 1. SEM Scanner in use

Figure2. SEM measurement sites

Materials & Methods


Acute care patients in a combined orthopaedic/plastic surgery ward in Cork University Hospital, Ireland.


Waterlow Score ≥ 10 (‘at risk’ to ‘very high risk’ of PU)


12 weeks

Target anatomical locations

Three consecutive readings taken over sacrum, heels, hips and ischial tuberosities


SEM Scanner (Bruin Biometrics LLC): plus training and induction

Tissue assessment criteria

  • SEM ∆ scores of ≥0.6 = increased risk of PU
  • Blanching or non-blanching (Category 1)3 erythema


  • Turning & mobilisation regimen
  • Pressure redistribution mattress/cushion
  • Heel elevation

Outcome measurements

  • SEM scan findings & visual skin assessment
  • Preventative care interventions
  • Number of HAPU across the study population compared to pre-evaluation data


32 subjects were evaluated over a 12-week period; 23 (72%) had evidence of incipient tissue damage detected by SEM scan (fig. 3).

Figure 3. Positive SEM (Δ≥0.6)

Of the 15 subjects with no visible signs of damage, 33% (n=5) had a positive SEM scan result, indicative of underlying PU (fig. 4).

Figure 4. Non-visible tissue damage

Across all anatomical locations, positive SEM scans picked up areas of pressure injury that were not apparent on visual skin assessment (fig. 5). Preventative interventions were initiated or ‘stepped up’ based upon SEM findings.

Figure 5. SEM vs. VSA

SEM scanning represents an exciting innovation that offers, for the first time, a method of objectively assessing tissue health at the bedside before damage becomes visible. During this evaluation, real-time quantitative data identified 23 (72%) subjects with evidence of underlying tissue damage compared to 17 (53%) subjects diagnosed by visual skin assessment. When positive readings were recorded (SEM Δ ≥ 0.6), frontline staff were prompted to implement targeted interventions/changes in patients’ pressure area care, with five subjects potentially receiving preventative measures that they may not have otherwise had.

That no subject developed a pressure ulcer during the evaluation, compared to an historic HAPU rate of 12.2%, underpins the potential benefit of including SEM scans into routine clinical assessment.

Key Points

  • SEM Scanner provides real-time, objective data at the bedside
  • SEM is indicative of pathological changes in the tissue
  • SEM is  frequently detected before skin redness is visible
  • Scan results can be used to trigger interventions getting help to the right patient at the right time
  • Early intervention can reduce the risk of HAPU


We are grateful for the help and support of Caroline Costello CNM 2 Ward 2A; Orlaith Hogan CNM 2 CUH; Nurses and HCAs of Ward 2A, CUH. Thank you!


1.Moore Z, Patton D, Rhodes SL, O’Connor T. Subepidermal moisture (SEM) and bioimpedance: a literature review of a novel method for early detection of pressure-induced tissue damage (pressure ulcers). Int Wound J. 2017;14(2):331-337

2.Oliveria AL, Moore Z, O’Connor T, Patton D. Accuracy of ultrasound, thermography and subepidermal moisture in predicting pressure ulcers: a systematic review. Journal of Wound Care. 2017; (5):199-212.

3.National Pressure Ulcer Advisory Panel, European Pressure Ulcer Advisory panel and Pan Pacific Pressure Injury Alliance. Prevention and Treatment of Pressure Ulcers: Clinical Practice Guideline. Emily Haesler (Ed.). Cambridge Media: Osborne Park, Western Australia; 2014