Ankylosing spondylitis （AS） is a chronic progressive inflammatory disease characterized by stiffness and pain in the lower back and sacroiliac joints， often accompanied by extra-articular manifestations. In traditional Chinese medicine （TCM）， it is classified as a type of "

Bi Disease

"， with lesions located in the bladder meridian and the governor vessel， both closely related to the kidney. Tongue diagnosis is an important component of traditional TCM diagnostic methods. The kidney pulse of the foot

Shaoyin

meridian is connected to the tongue base， and the tongue root reflects kidney function. Therefore， tongue examination can fully reflect kidney pathology and plays a decisive role in the diagnosis and syndrome differentiation of AS. Since AS is fundamentally related to kidney and governor vessel deficiency， with the kidney as the main site of pathology， careful observation of tongue characteristics， including tongue color， shape， coating color， and coating texture， can reveal the disease's progression. This provides important guidance and reference for clinical syndrome differentiation， prescription selection， drug application， and the prediction of disease course and prognosis in AS.