Among people with established AF, the current ESC NT-proBNP referral threshold of 125 pg/mL is an excellent rule-out test for HF with a high NPV (97.3%, 95% CI [96.5, 98.0]) and sensitivity (98.8%, 95% CI [98.5, 99.1]) but most patients (89.7%) will have a raised result and be referred for specialist assessment. This evidence concerns the gene NPPB and hydrops fetalis.