Comparative Analysis of Tongue Indices between Patients with and without a Self-Reported Yin Deficiency: A Cross-Sectional Study

Abstract

We investigated the hypothesis that Yin-deficient patients have a reddened tongue with less coating. We screened 189 participants aged 20 to 49 years, complaining of headache. To classify patients in terms of Yin deficiency, we used two self-reporting Yin-deficiency questionnaires (Yin-Deficiency Questionnaire and Yin-Deficiency Scale) and diagnosis by a doctor. Based on the tests, a total of 33 subjects were assigned to a Yin-deficient group and 33 subjects were assigned to a nondeficient control group. Tongue images were acquired using a computerized tongue diagnostic system, for evaluating tongue indices. The tongue coating percentage and tongue redness were calculated as the mean a^⁎ value of both the whole tongue area (WT a^⁎) and the tongue body area (TB a^⁎). The tongue coating percentage of the Yin-deficient group (34.79 ± 10.76) was lower than that of the nondeficient group (44.13 ± 14.08). The WT a^⁎ value of the Yin-deficient group (19.39 ± 1.52) was significantly higher than that of the nondeficient group (18.21 ± 2.06). However, the difference in the TB a^⁎ value between the two groups was not significant. In conclusion, we verified that Yin-deficient patients had less tongue coating and tended to have a more reddish tongue than nondeficient patients.

Figure 1

Flow chart of the experimental design of the present study. YDS: Yin-Deficiency Scale; YDQ: Yin-Deficiency Questionnaire; YD: Yin deficiency; CTDS: computerized tongue diagnostic system.

Figure 2

Calculation of tongue indices. The tongue area was extracted from an acquired tongue image. The tongue coating area was distinguished from the tongue body area based on the difference in color. The RGB color values in the areas of interest were converted into CIE-L^∗a^∗b^∗ color values. Then, the mean L^∗a^∗b^∗ values of whole tongue area and tongue body area were calculated. The tongue coating percentage was calculated as the percentage of the pixel number of the tongue coating area to the pixel numbers of the whole tongue area.

Figure 3

Comparison of the tongue indices between the Yin-deficient group and the nondeficient control group. The tongue coating percentage of Yin-deficiency (YD) group (34.79%) was significantly lower than that of the control group (44.13%). The mean a^∗ value of whole tongue area (WT a^∗) was significantly different between the two groups; the WT a^∗ value of the Yin-deficient group (19.39 ± 1.52) was higher than that of the control group (18.21 ± 2.06). However, the mean a^∗ value of tongue body was not significantly different between the two groups. Vertical bars: ±SD; ^∗∗p < 0.01; n.s.: not significant.

Figure 4

Logistic regression curve. Decrease of tongue coating percentage indicates an increased probability of Yin deficiency. [Probability of Yin deficiency = exp(0.06X − 2.368)/(1 + exp(0.06X − 2.368)); X = tongue coating percentage (%)].

Figure 5

Representative tongue images from the Yin-deficient and control groups. A tongue coating percentage was used as an index to estimate the amount of tongue coating. The redness of the tongue was measured as the mean a^∗ value of both the whole tongue area and the tongue body area that remained after excluding the tongue coating area. (a) A tongue image of a Yin-deficient patient is shown, and (b) a tongue image from a nondeficient control patient is shown. Note that these examples show that the tongue coating percentage of the Yin-deficient patient is lower and that the mean a^∗ value of the whole tongue area is higher than those of the nondeficient patient. The mean a^∗ value of the tongue body area showed a relatively small difference between the two samples.