Quality-recommendation paradox in adult hypothyroidism guidelines: a systematic appraisal of methodological quality, recommendation consistency, and citation impact

Background Hypothyroidism is one of the most common endocrine disorders, yet its adult guidelines disagree on screening, on treatment thresholds for subclinical disease, and on combination therapy. Whether higher methodological quality yields more conservative, more actionable, or more influential guidance remains unclear. Methods PubMed, Web of Science, Scopus, CNKI, and VIP were searched from January 1, 2010 to August 25, 2026. Eligible documents were clinical practice guidelines and standard documents for adult hypothyroidism, published in Chinese or English. Four raters assessed all included documents with the Appraisal of Guidelines for Research and Evaluation II (AGREE II) instrument. Domain scores, intraclass correlation coefficients (ICCs), recommendation consistency, version evolution, emerging-topic coverage, and citation impact were examined. The study was registered with the International Prospective Register of Systematic Reviews (PROSPERO; CRD420261487294). Results Fifteen guidelines were included: 12 English and 3 Chinese documents (2012-2025). Eight of 15 reached an overall quality score of at least 5.5 and were recommended for use. BMJ 2019 (6.25), AACE/ATA 2012 (6.20), and ETA 2025 (6.10) scored highest, and the two Chinese primary care guidelines scored lowest (4.86 and 4.77). For the thyroid-stimulating hormone (TSH) 4–10 mIU/L gray zone, BMJ 2019 avoided routine treatment, whereas ETA 2013 (5.76) was more interventional. Version evolution was evidence-driven in the ETA series but simplification-driven in Chinese primary care documents, and coverage of artificial intelligence, laboratory standardization, and reference intervals was largely descriptive. Exploratory analysis showed only weak quality-citation correlation (Spearman rho = 0.368, n = 13). Average ICC(2,k) values ranged from 0.651 to 0.895 across domains. Conclusion Mean overall quality ranged from 4.77 to 6.25, and only 8 of 15 (53%) earned an unqualified recommendation for use; the most rigorous documents were BMJ Rapid Recommendations, AACE/ATA 2012, and ETA 2025. Rigorous guidelines often acknowledge uncertainty, whereas less rigorous documents supply clearer directives. In gray-zone decisions such as TSH 4–10 mIU/L, clinicians should pair guideline appraisal with explicit evidence summaries and should not assume that the most decisive advice is the most reliable. Guideline developers should strengthen stakeholder involvement, applicability, and scheduled updating.