Reliability of Low-Cost Thermometers for Monitoring Foot Temperature

In the United States, the prevalence of diabetes is high and often burdens those who are economically disadvantaged. Considering the risk for foot and skin complications in those with diabetes, foot temperature monitoring has been shown to help mitigate plantar ulceration risk. Higher cost thermometers have been demonstrated reliable. Validation of lower cost thermometers could improve access to those who are often underserved. 

Purpose: To assess each device's repeatability, intra-rater and inter-rater reliability, and ease of use. Methods: Three inexpensive infrared thermometers ($25 or less) were compared against a clinically tested reference thermometer for repeatability (25 measures on three different days). Rater reliability was assessed by two raters using three trials per site location (1st metatarsal head, 3rd metatarsal head, and heel) across 25 subjects. Feasibility was assessed by asking the subjects to rank the thermometers after testing the thermometers on the same three locations. 

Data Analysis: Descriptive statistics including mean, standard deviation, and coefficient of variation (CV) were used for device repeatability. Intra-class correlation coefficient was used to assess rater reliability. Results: 25 subjects aged 23 to 80 years old (mean = 49.6±15.8 years). Across 25 measures on three different days, the devices had CVs ranging from 0.20% to 0.91%. When all days were combined, CVs ranged from 3.32% to 4.69%. Intra-rater reliability using ICC was >0.99 for both researchers and all thermometers. Reliability between the two researchers was excellent across the thermometers (ICC 0.965 - 0.975). The thermometer with the highest rank was ranked because of its comfort, ease of handling, size, and the presence of a light. 

Discussion: The study was designed to assess the repeatability and reliability of three low-cost thermometers. Reliability and repeatability were good and the measurements correlated strongly to very strongly with the reference device. The subjects demonstrated little difficulty using the thermometers with limited instruction.

Conclusions: Monitoring skin temperature has been shown to be a useful tool to minimize risk of foot ulceration in those with diabetes. Inexpensive, commercially available infrared thermometers can be a reliable and valid way to assess local skin temperature.