Methodological quality and clinical applicability of long COVID guidelines and scientific statements: a systematic review using AGREE II and AGREE-REX

Introduction: Long COVID is projected to affect 0.6 to 1.0% of the population between 2025 and 2030. This study reviewed the methodological quality, clinical applicability and content of the care recommendations issued for adults ≥18 years with long COVID in clinical practice guidelines (CPGs) and scientific statements (SSs). Methods: Registered in PROSPERO (CRD420261324906). PubMed, Scopus, trip, five guideline repositories and national health portals were searched between February and April 2026, and PubMed and Scopus were updated on 2 September 2026. Eligible documents were CPGs and SSs on adults with suspected or confirmed long COVID, published in English or Spanish. Screening and full-text review were duplicated independently; data were extracted by one reviewer and verified by a second. Methodological quality was appraised with AGREE II, reporting the six standardised domain scores separately, each rescaled within its domain and never summed into an overall score; applicability was appraised with AGREE-REX. A narrative synthesis covered five predefined care domains. Results: Twenty documents were appraised, 19 from the initial search and one from the update. From the 19 initial documents, 510 recommendations were extracted across five NICE-derived domains, mostly clinical management (63.3%) and care planning (29.6%). Quality was uneven (rigor of development 16.7-97.9%; applicability 0.0-95.8%; editorial Independence median 100%), and only one document reported a GRADE-compatible evidence-to-decision framework. Four documents were prioritised and contributed 99 recommendations; they scored higher than the remaining corpus in all six domains, yet applicability remained their weakest (68%). AGREE-REX showed recommendations directed far more clearly at clinicians than at patients or decision-makers. Content converged on shared decision-making, multidisciplinary rehabilitation, patient-centered care and return-to-work support. Discussion: Guidance on long COVID is abundant but methodologically uneven, and the unevenness is concentrated in how evidence is linked to recommendations and in applicability. The corpus offers well-formulated clinical content whose evidence-to-decision reasoning and implementation requirements are seldom reported, and it therefore requires formal contextual adaptation, for example through GRADE-ADOLOPMENT, before use. Key limitations are the scarcity of guidance from low- and middle-income countries and the diversity of development methods. Systematic review registration: https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD420261324906, Identifier CRD420261324906.