In acupuncture therapy, diagnosis, acupoints, and stimulation for patients with the same illness are often inconsistent among between Traditional Chinese Medicine (TCM) practitioners. This is in part due to the paucity of evidence-based diagnostic methods in TCM. To solve this problem, establishment of validated diagnostic tool is inevitable. We first applied the Item Response Theory (IRT) model to the Five Viscera Score (FVS) to test its validity by evaluating the ability of the questionnaire items to identify an individual's latent traits. Next, the health-related QOL scale (SF-36), a suitable instrument for evaluating acupuncture therapy, was administered to evaluate whether the FVS can be used to make a health-related diagnosis. All 20 items of the FVS had adequate item discrimination, and 13 items had high item discrimination power. Measurement accuracy was suited for application in a range of individuals, from healthy to symptomatic. When the FVS and SF-36 were administered to other subjects, a part of which overlap with the first subjects, we found an association between the two scales, and the same findings were obtained when symptomatic and asymptomatic subjects were compared regardless of age and sex. In conclusion, the FVS may be effective in clinical diagnosis.