The goal of this clinical trial is to learn whether a simple blood test screening pathway can help diagnose heart failure earlier in adults in primary care who take loop diuretic medicines (such as furosemide or bumetanide) but do not have a recorded diagnosis of heart failure.

The main questions it aims to answer are:

1. Does offering a NT-proBNP blood test to eligible patients increase the number of new heart failure diagnoses within 12 months compared with usual care?
2. Does this screening pathway also uncover other important heart problems, such as irregular heart rhythms (arrhythmias) or valve disease?

This is a cluster randomised controlled trial, which means that whole GP practices, rather than individual patients, are randomly assigned to one of two approaches:

1. NT-proBNP screening pathway, in which eligible patients are invited for a NT-proBNP blood test
2. Usual care, in which patients continue to be managed as they normally would without proactive screening

Participants will:

Be identified from GP records if they are prescribed loop diuretics and have no prior diagnosis of heart failure

In screening practices, be invited to attend for a free finger-prick NT-proBNP blood test and brief questionnaire

Be referred to the heart failure team and invited for an echocardiogram (a heart ultrasound scan) and further assessment if their NT-proBNP level is higher than 125 pg/mL

Researchers will compare outcomes between screening and usual-care practices after 12 months, focusing on new diagnoses of heart failure. They will also look at other important cardiovascular findings, such as new arrhythmias, valve disease, and heart failure hospitalisation rates.

Inclusion Criteria:

• Receiving a loop diuretic (furosemide, bumetanide or torsemide)
• No coded diagnosis of heart failure in GP records
• Never had a natriuretic peptide test
• Willing to have a blood test for NT-proBNP

Exclusion Criteria:

• Clinical Frailty Score 7 or above on Rockwood frailty scale
• Prior diagnosis of heart failure
• Prior natriuretic peptide testing