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Background and Aims Our tertiary ILD centre routinely monitors liver function tests (LFTs) 3 monthly for patients established on Nintedanib. However, beyond the initial 3 months the requirement for monitoring is ‘periodically thereafter or as clinically indicated’. 1 We aimed to identify the prevalence of clinically relevant abnormal LFTs identified on routine scheduled testing, and the value of routine monitoring (cost £4.34 per LFT).Methods We retrospectively reviewed all local patients who initiated Nintedanib for idiopathic pulmonary fibrosis (IPF) or progressive pulmonary fibrosis (PFILD) at our ILD centre between February 2014 and October 2024. We reviewed all LFT results taken after 3 months of initiating medication, categorising tests into routine or acute, identified all abnormal results, their circumstances and outcomes. Fisher’s exact test was used for group comparisons.Results 404 patients initiated Nintedanib (313 IPF, 91 PFILD), with a mean 543 days on treatment (range 1 - 4,901 days). The cumulative exposure to Nintedanib was 175,124 patient-days, requiring 1,918 routine tests.Routine testing after 3 months identified 41 patients with abnormal LFTs (1 abnormal result every 46.8 tests), of which 36(88%) were <3x upper limit of normal (ULN), with none >5x ULN (table 1). 30(73%) had asymptomatic rises in ALT, 29 requiring no action, and one patient requiring a treatment break then restarted medication (this test was likely haemolysed). 11 patients had abnormal ALTs associated with gastrointestinal symptoms or new medications, of which 7(64%) patients required treatment breaks or stopped treatment. Overall, we had 1 abnormal routine test resulting in changed management every 239.8 tests (cost per clinically relevant abnormal test £1040.52).A further 26 patients had abnormal LFTs on acute testing outside of routine schedules either related or unrelated to Nintedanib treatment, necessitating treatment breaks or stopping treatment in just 4(15%) patients.Abstract P88 Table 1Abnormal routine ALT test resultsDiscussion Routine LFT monitoring after 3 months rarely identified clinically relevant rises in ALT and came at a significant time and monetary cost for our ILD service. We are developing an optional patient-initiated follow up (PIFU) pathway for monitoring LFTs in patients who are stable on treatment.Reference OFEV® (nintedanib) Prescribing Information. Ridgefield, CT: Boehringer Ingelheim Pharmaceuticals, Inc; 2022.