Clinical evidence and references

In plain language

Comparing the same spot on your left and right foot is the method used in the research. A difference of about 2.2 °C (4 °F) is the figure most often quoted as a reason to slow down and get the foot looked at.
That figure is a widely used warning trigger, not a test result. A smaller difference does not mean a foot is healthy, and a larger one does not confirm any condition.
The top of the foot matters too. A warm, swollen midfoot can be an early sign of Charcot (neuropathic) arthropathy, which is why PodiaScan asks for a top-of-foot reading as well as the sole.
There is no separately proven cut-off for the top of the foot. We use the same 2.2 °C figure so the reading is easy to understand, and we say clearly that it is a prompt to seek review, not a diagnosis.
If both feet are affected, left-versus-right comparison can miss the problem — both feet may be warm. Temperature alone can neither confirm nor rule out Charcot.
Take readings the same way each time: rest first, same room, same thermometer, same distance, same points on the foot.

What the guidelines say

PodiaScan complements the HSE Model of Care for the Diabetic Foot and supports the daily foot-checking habit recommended by Diabetes Ireland. Its temperature-monitoring method is based on separate international peer-reviewed research and does not replace professional screening.

The 2023 IWGDF guideline on the diagnosis and treatment of active Charcot neuro-osteoarthropathy notes that a temperature difference of around 2 °C (4 °F) between the affected foot and the same point on the other foot is commonly used in practice, while stating that its diagnostic accuracy has not been established. It recommends standardised, repeated measurement, and notes that where both feet are affected — or one limb is absent — a left-right comparison is unreliable and an ascending toe-to-knee gradient has been suggested instead. No evidence-based cut-off for deciding that Charcot has gone into remission is endorsed.

The 2.2 °C home-monitoring figure itself comes from randomised trials of daily foot temperature self-checks in people at high risk of ulceration, where patients were asked to contact their nurse and reduce activity when corresponding sites differed by more than 4 °F (2.2 °C).

A published critical appraisal of that rule points out that it was adopted pragmatically rather than derived statistically, and that thresholds, sites and measurement conditions vary between studies.

What this means for how PodiaScan behaves

Differences of 1.5 °C to 2.1 °C are shown as “watch”; 2.2 °C and above are shown as an alert. The same figures apply to the top-of-foot zone.
Alerts are prompts to look at the foot and seek review. They are not clinical findings and no clinical algorithm is applied.
Clinician reports state what was measured and include a caution that both-foot (bilateral) involvement reduces the reliability of left-right comparison.

References

Health Service Executive. Model of Care for the Diabetic Foot. HSE publication
Diabetes Ireland. Footcare guidance for people living with diabetes. Diabetes Ireland foot-care guidance
IWGDF. Guideline on the diagnosis and treatment of active Charcot neuro-osteoarthropathy in persons with diabetes mellitus (2023). Full guideline (PDF) · Diabetes Metab Res Rev, doi:10.1002/dmrr.3646
Jones PJ, et al. Systematic review of the diagnosis of active Charcot neuro-osteoarthropathy (2023). PubMed 36728905
Lavery LA, Higgins KR, Lanctot DR, et al. Preventing diabetic foot ulcer recurrence in high-risk patients: use of temperature monitoring as a self-assessment tool. Diabetes Care 2007;30(1):14–20.
Armstrong DG, Holtz-Neiderer K, Wendel C, et al. Skin temperature monitoring reduces the risk for diabetic foot ulceration in high-risk patients. American Journal of Medicine 2007;120(12):1042–1046.
van Netten JJ, et al. Critical appraisal of the >2.2 °C temperature-difference rule. doi:10.1177/15347346211062719
Dallimore SM, et al. Infrared thermometry reliability in the diabetic foot. doi:10.1186/s13047-020-00421-z
WOUNDS. Review of the IWGDF recommendations (2024). doi:10.25270/wnds/24029
IWGDF guidelines home: iwgdfguidelines.org
“It’s an important metric to measure, particularly with the complications associated with increased temp. It’s an easy tool and can inform clinicians guiding treatment and quicker pathway of management.”
— Prof. Sarah Curran. Professor of Podiatric Medicine and Rehabilitation

Important

PodiaScan is a record-keeping and measurement tool. It is not a diagnostic device and does not replace examination by a qualified healthcare professional. If you have a warm, red, swollen or misshapen foot, pain, an open wound, fever or a foot that suddenly looks different, seek medical advice the same day.