Reliability and validity of tongue color analysis in the prediction of symptom patterns in terms of East Asian Medicine

OBJECTIVE:To examine whether color parameters of tongue inspection(TI)using a digital camera was reliable and valid,and to examine which color parameters serve as predictors of symptom patterns in terms of East Asian medicine(EAM).METHODS:Two hundred female subjects'tongue substances were photographed by a mega-pixel digital camera.Together with the photographs,the subjects were asked to complete Yin deficiency,Phlegm pattern,and Cold-Heat pattern questionnaires.Using three sets of digital imaging software,each digital image was exposure-and white balance-corrected,and finally L*(luminance),a*(red-green balance),and b*(yellow-blue balance)values of the tongues werecalculated.To examine intra-and inter-rater reliabilities and criterion validity of the color analysis method,three raters were asked to calculate color parameters for 20 digital image samples.Finally,four hierarchical regression models were formed.RESULTS:Color parameters showed good or excellent reliability(0.627-0.887 for intra-class correlation coefficients)and significant criterion validity(0.523-0.718 for Spearman's correlation).In the hierarchical regression models,age was a significant predictor of Yin deficiency(β=0.192),and b*value of the tip of the tongue was a determinant predictor of Yin deficiency,Phlegm,and Heat patterns(β=-0.212,-0.172,and-0.163).Luminance(L*)was predictive of Yin deficiency(β=-0.172)and Cold(β=0.173)pattern.CONCLUSION:Our results suggest that color analysis of the tongue using the L*a*b*system is reliable and valid,and that color parameters partially serve as symptom pattern predictors in EAM practice.