What are the key diagnostic criteria for sarcoidosis in a patient presenting with respiratory symptoms?

Key diagnostic criteria for sarcoidosis in a patient presenting with respiratory symptoms include a combination of clinical, radiological, and histological findings supported by exclusion of other diseases.

Clinically, patients often present with respiratory symptoms such as cough, dyspnoea, or chest discomfort, but these are nonspecific and require further investigation ¹.

Radiologically, chest X-ray and high-resolution CT scans are essential initial investigations. Typical findings include bilateral hilar lymphadenopathy, pulmonary infiltrates, or fibrosis consistent with sarcoidosis stages I to IV ¹.

Histological confirmation is critical and involves demonstrating non-caseating granulomas on tissue biopsy from accessible sites such as lymph nodes, lung tissue (via bronchoscopy with transbronchial biopsy), or other affected organs, while excluding infections like tuberculosis and malignancy ¹[(Culver, 2015)].

Additional investigations include bronchoscopy with bronchoalveolar lavage showing lymphocytosis and elevated CD4/CD8 ratio, which supports the diagnosis but is not definitive alone ¹[(Jeny et al., 2020)].

Exclusion of alternative diagnoses such as tuberculosis is mandatory, often requiring microbiological cultures and nucleic acid amplification tests on respiratory samples ¹,³.

Serum markers such as elevated angiotensin-converting enzyme (ACE) levels may support the diagnosis but lack specificity and are not diagnostic alone [(Rosen, 2007)].

Referral to secondary care specialists is recommended for further assessment and confirmation, with multidisciplinary input if multiple organ systems are involved ¹.