Subepidermal moisture as a biomarker demonstrates benefits for early pressure ulcer detection


A study that aimed to evaluate the sensitivity and specificity of subepidermal moisture (SEM)—a biomarker employed for the early detection of pressure ulcers—has demonstrated that SEM biocapacitance measures “can complement clinical skin and tissue assessments (STAs)”. Published in Wound Repair and Regeneration, the investigation also shows that using SEM as a biomarker may highlight the risk of specific anatomies developing pressure ulcers.

First author Henry Okonkwo (Seacliff Healthcare Center, Los Angeles, USA), Ruth Bryant (Abbott Northwestern Hospital, Minneapolis, USA) and colleagues reveal that prevention programmes for pressure ulcers, which are a common complication of reduced patient mobility and occur in over 2.5 million US patients, usually consist of “a combination of pressure ulcer risk assessments, supplemented by STAs and mechanical offloading (such as patient repositioning and the use of pressure redistributing mattresses and medical devices)”.

Introducing their investigation, the authors cite the 2014 global Clinical Practice Guideline of the US National Pressure Ulcer Advisory Panel (NPUAP), European Pressure Ulcer Advisory Panel (EPUAP), and Pan Pacific Pressure Injury Alliance (PPPIA), which states that “the condition of skin and underlying tissue can serve as an indicator of early signs of pressure damage, therefore routine STAs provide an opportunity for early identification and treatment of skin alterations, especially pressure ulcers”.

However, these bodies also found that due to the subjective, latent nature of STAs—often performed by nurses—there is a “clear need” for an objective, point‐of‐care tool for diagnosing or assessing the development of pressure ulcers in patients at a higher risk of injury.

A change in SEM, which can be detected by point-of-care devices that measure changes in biocapacitance, is a biomarker of a developing pressure ulcer and—according to Okonkwo et al—precedes the appearance of visible or palpable skin changes by approximately three to 10 days.

In order to test this, a multicentre (n=12), blinded, prospective, longitudinal clinical study, conducted in both the USA and UK, set out to compare the use of SEM as a biomarker, compared with the “gold standard” of STAs. Moreover, investigators wanted to “characterise the timing of SEM changes relative to the diagnosis of a pressure ulcer”.

ruth bryant
Co-author Ruth Bryant

A total of 189 patients (n=182 in intention‐to‐treat population) were enrolled at acute and post‐acute sites, with data “collected from […] heels and sacrums using a biocapacitance measurement device, beginning at admission and continuing for a minimum of six days to: the patient developing a pressure ulcer; discharge from care; or a maximum of 21 days”.

Explaining the results, Okonkwo et al write: “Of the intention-to-treat population, 26.4% developed a pressure ulcer during the study; 66.7% (n=32) classified as stage 1 injuries, 23% (n=11) deep tissue injuries, [with] the remaining being stage 2 or unstageable (10.5%; n=5). Sensitivity was 87.5% (95% CI: 74.8–95.3%) and specificity was 32.9% (95% CI: 28.3–37.8%).”

SEM changes were observed 4.7 (±2.4) days earlier than diagnosis of a pressure ulcer by STA alone, though “latency between the SEM biomarker and later onset of a pressure ulcer, in combination with standard of care interventions administered to at‐risk patients, may have confounded specificity”. Furthermore, the sensitivity and specificity of SEM as a biomarker exceeded that of clinical judgment alone.

The investigators concluded: “While acknowledging specificity limitations, these data suggest that SEM biocapacitance measures can complement STAs, facilitate earlier identification of the risk of specific anatomies developing pressure ulcers, and inform earlier anatomy‐specific intervention decisions than STAs alone. Future work should include cost‐consequence analyses of SEM-informed interventions.”

“Even though not all anatomies exhibiting elevated SEM deltas will proceed to eventually develop a pressure ulcer, it is important for healthcare providers to be aware of the early warning signs so they can take risk‐appropriate mitigating steps. Pressure ulcers often occur without prior visual and palpable cues appearing in time to prevent them, especially if the injury is not superficial,” Okonkwo and colleagues added.


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