BackgroundShortened telomere length (TL) is a genomic risk factor for fibrotic interstitial lung disease (ILD), but its role in clinical management is unknown. Research QuestionWhat is the clinical impact of TL testing on the management of ILD? Study Design and MethodsPatients were evaluated in the Columbia University ILD clinic and underwent CLIA-certified TL testing by flow cytometry and fluorescence in-situ hybridization (FlowFISH) as part of clinical management. Short TL was defined as below the 10th age-adjusted percentile for either granulocytes or lymphocytes by FlowFISH. Patients were offered genetic counseling and testing if they had short TL or a family history of ILD. FlowFISH TL was compared against research qPCR TL measurement. ResultsA total of 108 patients underwent TL testing, including those with clinical features of short telomere syndrome such as familial pulmonary fibrosis (50%) or extrapulmonary manifestations in the patient (25%) or a relative (41%). The overall prevalence of short TL was 46% and was similar across clinical ILD diagnoses. The number of short telomere clinical features was independently associated with detecting short TL (OR 2.00, 95% CI [1.27, 3.32]). TL testing led to clinical management changes for 35 (32%) patients, most commonly resulting in reduction or avoidance of immunosuppression. Of the patients who underwent genetic testing (n=34), a positive or candidate diagnostic finding in telomere-related genes was identified in 10 (29%) patients. Inclusion of TL testing below the 1st percentile helped reclassify 8 of 9 variants of uncertain significance (VUS) into actionable findings. The qPCR test correlated with FlowFISH, but age-adjusted percentile cutoffs may not be equivalent between the two assays. InterpretationIncorporating TL testing in ILD impacted clinical management and led to the discovery of new actionable genetic variants.