The association between objective tongue color and endoscopic findings: results from the Kyushu and Okinawa population study (KOPS)

Study population and study protocol

The current study began in 2007 as a survey of the incidence of vascular events associated
with lifestyle-related disease among the general population as a part of the Kyushu
and Okinawa Population Study (KOPS) 19]–22]. Our study was conducted with residents of Ishigaki City, Okinawa Prefecture who
participated in a program of esopahagogastroduodenoscope screening for gastric cancer
between October 2012 and January 2013. In the study protocol, after giving informed
consent, the tongue was photographed. The photography was conducted in a shady controlled
room. The subject’s face was fixed with a chin rest and a forehead rest. As the mouth
cannot be opened when both chin and forehead are fixed, first the chin is placed on
the chin rest and, after swallowing saliva, the mouth is opened and the tongue extended,
following which the forehead is placed against the forehead rest. Each tongue extension
is for 20s, and images are taken every 100 ms, for a total of 200 images. After that
the operator visually confirmed the tongue color. Secondly, esophagogastroduodenoscopy
was done, blood was taken to check for serum antibody to H.pylori (anti-H.pylori), and serum pepsinogen (PG) I /II and gastrin were measured. We then estimated the
associations between tongue color, the endoscopic findings, H.pylori infection status, and serological atrophic gastritis. Tongue color was measured by
the device-independent international commission on Illumination (CIE) 1976 L*a*b*
color space standards at four points: (1) tongue edge, (2) tongue posterior, (3) tongue
middle, and (4) tongue apex. The coating of the tongue does not grow on the edge of
the tongue, and the color of that point can be considered the color of the tongue
body. In contrast, at the other three points the color is a mixture of the coating
and the body of the tongue.

From the point of view of Kampo medicine, it is said that the posterior of the tongue
reflects kidney function (traditional medicine), the middle of the tongue reflects
the stomach and pancreas (GI tract traditional medicine), and the apex of the tongue
reflects the heart (traditional medicine). Therefore, we used these areas to assess
the association of tongue color with endoscopic findings. Fig. 1. shows an example of tongue color imaging. The value for this patient with erosive
gastritis (3a*, 3b*) is higher than that of the normal control.

Fig. 1. a) Example of tongue color from the normal group. Red indicates the tongue edge, green
the posterior, blue the middle, and orange the apex. b) Example of tongue color with erosive gastritis only

In addition, we calculated the ratio of the tongue edge to the other three points
measured to examine the association between the coating of the tongue and the endoscopic
and laboratory findings. By calculating the ratio to the tongue edge we can confirm
that the color of the tongue reflects the body of the tongue, not the coating.

Esophagogastroduodenoscopy was done for 919 residents, and the data of 896 residents
from whom we were able to get consent for the tongue color and blood test (age range
28–86 years; mean age 57.7 years; 390 men and 506 women) was available for analysis.

To ensure the validity of the data, all physicians participating in the study were
staff members of the Department of General Internal Medicine, Kyushu University Hospital
or the Department of General Medicine and Emergency Care, Toho University School of
Medicine Omori Hospital. All were trained with regard to the study protocol and the
medical procedures necessary for the study. The study protocol was approved by the
Ishigaki City Health Center and the Kyushu University Hospital Ethics Committee. Written
informed consent was obtained from all participants prior to the examination. Consent
to publish the images used was obtained from both of the patients featured. The study
was conducted in accordance with the principles of the Helsinki Declaration of 1975,
as revised in 2000.

Tongue image analyzing system (TIAS)

We previously reported on the functionality of the TIAS system, which is equipped
with a diffused light source for recording the state of the tongue surface 17], 18], 23]. In brief, when doing photography using TIAS (film image was 1280?×?1024-pixels),
calibration of the camera and light source is performed only once, when the power
is turned on. When photographing the subject using TIAS, many tongue photographs are
taken, from which one image is selected manually for tongue color analysis. We defined
the position of the four points by a ratio calculated by manually specifying five
points that define the shape of the tongue. The ratio used to determine the four measurement
points is illustrated in Fig. 2 The size of the measured tongue area was two 5 mm diameter circles and the measurement
of color value is calculated by the average of the two circles. The RGB values at
each point are then converted to CIE1976 L*a*b* color space, which is device independent
and is designed to be perceptually uniform. This means that a change of the same amount
in the L*, a*, or b* value should produce a change of the same visual importance.
A photograph taken with TIAS is shown in Fig. 3.

Fig. 2. We defined the position of the four points by a ratio calculated by manually specifying
five points that define the shape of the tongue

Fig. 3. A photograph taken by the Tongue Image Analyzing System (TIAS)

Esophagogastroduodenoscopy

Each participant underwent esophagastroduodenoscopy at the Ishigaki City Health Center
by highly experienced endoscopists who performed each examination without knowledge
of the serological data. The endoscopic examination was for esophageal hernia (EH),
erosive esophagitis (EE), erosive gastritis (EG), superficial gastritis (SG), gastric
ulcer (GU), gastric cancer (GC), erosive duodenitis (ED), duodenal ulcer (DU), and
duodenal cancer (DC). EE was defined according to the Los Angeles classifications
A-D 24]. GC was diagnosed based on the histological finding and the stage classification
and was determined through an evaluation of the clinical examination.

Testing for antibody to H.pylori

The blood samples of all participants were separated and stored at ?80 °C until testing.

The serum IgG level of HP was measured by a commercially available direct ELISA kit
(“E Plate ‘Eiken’ HP Antibody” Eiken Kagaku). This ELISA kit was developed in Japan
and uses antigen extracted from a domestic strain. It is commonly used in medical
studies 25]. Positivity for HP infection was defined as an anti-HP IgG antibody level greater
than 10 U/mL in serum.

Serum PG and gastrin measurement

Serum PG isozymes I and II were measured by a competitive-binding double-antibody
radioimmunoassay (PGI/PGIIRIA-BEAD, Abbott Japan Co., Ltd., Tokyo, Japan). The serum
gastrin level was measured using an RIA kit (Dinabot Co., Tokyo, Japan). Serological
atrophic gastritis was defined based on the results of a serum PGIlevel ?70 ng/ml
and a PGI/IIratio ?3.0. The assay has a sensitivity of 70.5 % and a specificity of
97.0 % for histological atrophic gastritis 26], 27]. Furthermore, we analyzed the serum PGIlevel as a marker gastric acid secretion 28].

Statistical analysis

Data are expressed as number (%), mean?±?SD, or median with quartiles [25 % – 75 %].
Participant characteristics and the tongue color calculated from tongue photography
were compared between participants with and without endoscopic findings, by H.pylori status, and by SAG using Fisher’s exact test for categorical variables and
unpaired t test or Mann–Whitney test for continuous variables. Variables with a difference
of P??0.1 in the univariate analysis were used in multivariate analysis to determine independent,
significant predictors. Odds ratios (OR) and 95 % Confident index (CI) were calculated
from the multiple logistic regression model after adjustment with each variable. All
statistical analyses were performed on a personal computer with the statistical package
SPSS 18.0 for windows.