Assessing skin temperature over time in a cohort of lower limb cellulitis: A methods comparison study
Authors: Cross Elizabeth LA , Llewelyn Martin J , Walker A Sarah , Hayward Gail N 
Published: December 2024

AbstractImportanceSkin temperature assessment is essential for the initial diagnosis of cellulitis and monitoring treatment response. Currently, this is subjective and can contribute to overdiagnosis.ObjectiveTo characterise skin temperature changes over time in cellulitis and compare two more objective measurement approaches, a thermal imaging camera (TIC) and a non-contact infrared thermometer (NCIT).DesignA methods comparison study nested within a prospective cohort. We measured limb temperatures daily for four days using a TIC and two NCITs (2-4 measurements/time points).SettingTwo acute hospitals in the United Kingdom’s National Health Service.ParticipantsAdults (age ≥18 years) diagnosed with lower limb cellulitis who attended hospital for antibiotic treatment.Main Outcome(s) and Measure(s)We used linear mixed-effects models to quantify changes in temperature over time and intraclass correlation coefficients (ICC) to assess reliability. We compared temperature measurements between devices using Lin’s concordance coefficients and Bland-Altman plots with estimated 95% limits of agreement (LOA).Results202 patients were included: 95% white ethnicity. The affected limb remained hotter than the unaffected limb across all days. Baseline affected limb temperatures varied between 33.1-36.9°C and limb temperature differences between 2.4-3.4°C, depending on the device. All devices showed significant reductions in affected limb temperature per day, with the largest decrease for the TIC (−0.34°C per day, 95%CI −0.48 to −0.19, P<0.001). Only the TIC and NCIT-1 showed significant reductions in limb temperature difference per day.All devices had excellent reliability (ICCs≥0.98). The TIC recorded, on average, affected limb temperatures that were lower than NCIT-1 and NCIT-2, by −2.52°C (95% LOA −5.47 to 0.43) and −4.67°C (95% LOA −6.53 to −2.82), respectively. The largest mean differences and the lowest Lin’s concordance coefficient were observed between the TIC and NCIT-2. The NCIT-2 also demonstrated evidence of proportional bias.Conclusions and RelevanceNCIT-2’s poorer performance suggests different NCITs cannot be used interchangeably. Neither the TIC nor NCIT-1 were clearly superior. More advanced analyses of thermal images could prove helpful. Future research should confirm our findings in different skin tones and aim to determine the clinical utility of potential earlier diagnosis or indications of therapeutic failure that thermal imaging might offer.Key PointsQuestionShould thermal imaging cameras (TICs) or non-contact infrared thermometers (NCITs) be used to measure skin temperature over time in lower limb cellulitis?FindingsIn this cohort of 202 adults, absolute affected limb temperature measurements varied widely between devices, including the two NCITs, but limb temperature differences were more similar. The TIC recorded the largest reduction in affected limb temperature over time (−0.34°C per day).MeaningNCITs’ measurement capabilities differ widely, so these devices cannot be used interchangeably. Due to this and the potential benefits of advanced thermal image analysis, TICs should be prioritised for further study in cellulitis.