Tongue Coating in COVID-19 Patients: A Case-Control Study

It has been suggested that COVID-19 patients have distinct tongue features, which may help to monitor the development of their condition. To determine if there was any specific tongue coating feature in COVID-19, this study investigated the difference in tongue coating between COVID-19 subjects and subjects with other acute inflammatory diseases characterized by fever. Tongue images taken with smartphones from three age-matched groups, namely, COVID group (n=92), non-COVID febrile group (n=92), and normal control group (n=92), were analyzed by two blinded raters according to a tongue coating scoring scheme, which assessed the levels of thick fur, slimy or greasy fur, discolored fur and composite index of tongue coating. Compared with control, significant increases in all coating indexes were found in the COVID group (P<0.001), as well as in the non-COVID febrile group (P<0.001). However, no difference was observed between COVID and non-COVID febrile groups for all coating indexes measured. In COVID-19 subjects, their scores of coating indexes had weak but significant correlations with certain inflammatory biomarkers, including WBC and neutrophil - lymphocyte ratio. It is concluded that COVID-19 subjects have pathological tongue coating patterns that are associated with inflammatory responses, and these coating patterns can help to indicate the direction of disease development.