Why is there an inconsistency between ICD10 code J84.1 (IPF) and J84.112?

These codes both refer to Idiopathic Pulmonary Fibrosis, while J84.112 is the more stringent and specific one to use. However, J84.112 is only familiar to US researchers as the J84.112 code exists only in the US ICD10-CM modification, and not in the Finnish ICD10 nor the international WHO version. If your endpoint of interest is IPF, J84.1 is the only code you can use within FinnGen for the time being.