Association Between A1c and Cutaneous Dermatophytosis: A Case–Control Study

ABSTRACT Background Patients with diabetes have an increased risk of certain dermatophytoses. However, less is known about dermatophyte infections in pre‐diabetic patients, or how A1c impacts risk. Objectives Assess the relationship between recent (< 1 year) HgbA1c status and odds of cutaneous dermatophyte infection. Methods Case–control study of patients seen at the University of Utah Dermatology Department between January 1, 2015 and December 21, 2022. Tinea cases were identified by ICD‐10 codes and required the diagnosis be made by a dermatologist. Controls included patients seen in the dermatology department but who had no known diagnosis (past or current) of dermatophyte infection and were seen in a context where tinea could have been identified (i.e., no surgical visits, suture removals, spot checks, and cosmetic visits) and did not have a potentially confounding condition (inflammatory rashes). The primary exposure examined was averaged HgbA1c 1 year before index visit. Secondary exposures included HgbA1c 3 months, 3–6 months, and 6–12 months before visit as well as 3 months after the visit. Sensitivity analysis was performed using categorised Hgb A1c and historical diagnosis of diabetes. Results There was a 1.16‐fold increase in the odds of tinea per point increase in averaged pre‐visit A1c (odds ratio [OR] 1.16; confidence interval [CI] 1.11–1.22). The odds of tinea for a given HgbA1c were higher for cutaneous tinea as compared to onychomycosis and tinea capitis. The odds of tinea were attenuated when adjusting for age and sex but remained significant (OR = 1.09; CI 1.03–1.15). Conclusions There was an association between averaged HgbA1c over the year before a visit and odds of tinea infection. This association was similar for individual A1c periods and was more pronounced for tinea infections outside of onychomycosis and tinea capitis. These data may support HgbA1c screening in patients with new dermatophytoses, or conversely may increase the suspicion of cutaneous dermatophytosis if HgbA1c is elevated.