Bronchoalveolar Lavage Fluid Lymphocytosis in Chronic Hypersensitivity Pneumonitis: A Systematic Review and Meta-Analysis.

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The role of bronchoalveolar lavage fluid (BAL) lymphocyte% to diagnose chronic hypersensitivity pneumonitis (CHP) is unclear. We conducted a systematic review and meta-analysis of BAL lymphocyte% in the diagnosis of CHP.We searched Medline, Embase and Cochrane library from inception to August 2019. Individual patient data were obtained to test performance characteristics of BAL lymphocyte% at different thresholds. Random-effects models were used for pooled estimates, with comparisons made between CHP and non-CHP interstitial lung diseases (ILD).Fifty-three studies were included in the systematic review and 42 in the meta-analysis. The pooled estimate for BAL lymphocyte% was 42.8% (95%CI 37.7-47.8, I2=95.3%) in CHP, 10.0% (95%CI 6.9-13.1, I2=91.2%) in idiopathic pulmonary fibrosis (IPF), 23.1% (95% CI 3.0-43.2, I2=85.2%) in non-IPF idiopathic interstitial pneumonia (IIP), 23.4% (95%CI 11.0-35.9, I2=45.7%) in connective-tissue disease ILD (CTD-ILD), and 31.2% (95% CI 17.6-44.8, I2=95.2%) in sarcoidosis. Results differed between CHP and IPF (p<0.0001), non-IPF IIP (p=0.0309), and CTD-ILD (p=0.0824), but not between sarcoidosis (p=0.0966). Using individual patient data from eight studies, lymphocyte% threshold >20% provided sensitivity of 68.1% and specificity of 64.8% for CHP. Higher thresholds provided lower sensitivity with higher specificity. Older age and ever having smoked were associated with lower lymphocyte% in CHP.BAL lymphocyte% is higher in CHP compared to IPF and other IIP, with higher thresholds providing improved specificity at the cost of sensitivity. However, parent studies are at risk of incorporation bias, and prospective studies should evaluate the additive discriminate value of BAL lymphocyte% to accurately diagnose CHP.

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