Background and Objectives: Persistent COVID-19 sequelae, often referred to as "long COVID", still constitute a major global medical challenge. In particular, general fatigue is the most widely reported, serious symptom. In the framework of Japanese traditional (Kampo) medicine (JTM), post-infection fatigue is frequently considered a "Qi deficiency", a significant loss of vital energy. In JTM, accurately diagnosing Qi deficiency is essential for determining the appropriate treatment. However, one challenge in JTM diagnosis is that mastering traditional diagnostic techniques takes time. We sought to validate the "Qi deficiency score", a quantitative patient-reported outcome measure designed to assess Qi deficiency in patients suffering from long COVID. Materials and Methods: This was a methodological study. We conducted a cross-sectional study of 237 patients who sought treatment at the post-COVID-19 clinic (COVID-19 Aftercare Clinic) at Okayama University Hospital. The patient population was randomly split into two cohorts: one for Exploratory Factor Analysis (EFA, n = 122) and another for Confirmatory Factor Analysis (CFA, n = 115). The simple Qi-deficiency score comprises eight items derived from Terasawa's diagnostic criteria, with a total range of 0-56. We evaluated internal consistency using Cronbach's α/McDonald's ω and examined structural validity. Convergent validity was established by examining correlations between the simple Qi deficiency score and the Fatigue Assessment Scale (FAS), the Self-rating Depression Scale (SDS), and Quality of Life (QOL) metric. Results: The score's internal consistency (α = 0.64 and ω = 0.63) was considered modest for screening traditional clinical syndromes. EFA showed major factors representing Qi deficiency symptoms. CFA supported a one-factor model with modest fit indices (CFI = 0.87; RMSEA = 0.079; SRMR = 0.077; TLI = 0.82). Factor loadings revealed that "Body feels tired (now)" (0.98) and "Tires easily (tendency)" (0.73) were the most significant symptoms. Convergent validity showed a strong positive correlation with the FAS (r = 0.61, ρ = 0.60) and a moderate correlation with the SDS (r = 0.55, ρ = 0.55). A significant negative correlation was found with QOL scores (r = -0.42, ρ = -0.43). Conclusions: The simple Qi deficiency score may be useful for evaluating Qi deficiency in patients with post-COVID-19 condition.
