Autologous Platelet Concentrate Bladder Injection for Refractory Overactive Bladder

Inclusion Criteria: 1. Adult participant aged 18 years or older with full capacity to understand the study and provide written informed consent. 2. Diagnosis of overactive bladder according to International Continence Society criteria: urinary urgency, usually with frequency and nocturia, with or without urgency urinary incontinence, in the absence of urinary tract infection or another obvious local, metabolic, or neurologic cause. 3. Refractory OAB, defined as persistent bothersome OAB symptoms after standard first-line behavioral therapy for at least 3 to 6 months, and inadequate response or intolerance to at least two oral medications with different mechanisms, such as antimuscarinic agents and beta-3 adrenergic agonists, after adequate treatment duration. 4. Other possible causes of OAB-like symptoms have been excluded by appropriate clinical evaluation, such as urinalysis, urine culture, ultrasound, urodynamic testing, and cystoscopy when clinically indicated. 5. Participant is unwilling, unsuitable, contraindicated, or has inadequate response to existing third-line treatments such as intradetrusor botulinum toxin injection or sacral neuromodulation. 6. General condition allows local anesthesia and cystoscopic bladder injection. 7. No absolute contraindication to autologous platelet concentrate / PRP treatment. 8. Willing to comply with study visits and follow-up assessments. Exclusion Criteria: 1. Platelet dysfunction syndrome or platelet count less than 50 x 10\^9/L. 2. Coagulation disorder or current anticoagulant therapy that may increase bleeding risk. 3. Active systemic infection or local infection at the injection site. 4. Active malignancy or history of malignancy within the past 5 years, especially urinary tract malignancy, or hematologic malignancy such as leukemia or lymphoma. 5. Active autoimmune disease judged by the investigator to increase risk or affect interpretation of results. 6. Pregnancy or lactation. 7. Known allergy to any component used in PRP preparation. 8. Untreated urinary tract infection. 9. Bladder stone, bladder tumor, bladder outlet obstruction, neurogenic bladder, interstitial cystitis / bladder pain syndrome, or another organic disease that explains OAB-like symptoms. 10. Prior intradetrusor botulinum toxin injection or sacral neuromodulation if excluded by the final protocol. 11. Severe cardiac, hepatic, or renal insufficiency; uncontrolled diabetes; severe anemia; or other systemic disease that may affect safety or wound healing. 12. Psychiatric illness, cognitive impairment, or other condition that prevents understanding of informed consent or reliable follow-up. 13. Recent use of nonsteroidal anti-inflammatory drugs or corticosteroids when judged by the investigator to interfere with PRP effect, unless discontinued for an appropriate washout period. 14. Expected survival shorter than the study period. 15. Refusal to sign informed consent or inability/unwillingness to comply with follow-up.