Sarcoidosis is a multi-organ disease and is characterized by sarcoidal noncaseating granuloma comprised of T-helper/inducer (CD4+) lymphocytes and scant cytotoxic (CD8+) T-lymphocytes. CD4+:CD8+ T-cell elevated ratio is a characteristic diagnostic parameter for sarcoidosis. This is the first report from Iran evaluating the CD4:CD8 ratio capability in differentiating pulmonary sarcoidosis from other interstitial lung diseases (ILDs) on a large cohort. Fifty pulmonary sarcoidosis patients and 50 non-sarcoidosis interstitial lung diseases (nsILDs) patients were included in the current study. Bronchoalveolar lavage (BAL) was performed using flexible fiberoptic bronchoscopy and flow cytometer. Non-sarcoidosis group was established by 50 components that were classified into eight subgroups. Fifty-two percent of sarcoidosis patients and 62% of non-sarcoidosis interstitial lung disease patients had normal spirometric results. The CD4/CD8 ratio was significantly higher in sarcoidosis than in non-sarcoidosis interstitial lung diseases (p 3.5 in 33.3%, 2.5-3.5 in 7.1%, 1.5-2.5 in 20.2% and < 1.5 in 39.4% of the entire study population. The best cut off point was 1.1 with the sensitivity of 92% and specificity of 80% for distinguishing sarcoidosis from other interstitial lung diseases. Performing bronchoalveolar lavage as the safe and rapid first step confirms the diagnosis of sarcoidosis in 92% of cases (current study sensitivity). Hence, performing an invasive procedure was required in a few patients only. Bronchoalveolar lavage flow cytometry in the assessment of clinical and radiological findings supplies an appropriate diagnostic adjunct for discriminating sarcoidosis from non-sarcoidosis interstitial lung diseases
