The research, published in PLOS Medicine, looked at over 155,000 people who had an NT-proBNP blood test ordered by their GP between 2004 and 2018. NT-proBNP helps GPs decide whether someone with symptoms such as breathlessness or tiredness might have heart failure and should be referred for specialist assessment. Currently, there is a single threshold used to decide whether or not an NT-proBNP is elevated and usually only those with a positive result are referred on for further assessment.
The study used anonymised electronic health records from the Clinical Practice Research Datalink (CPRD), which includes data from GP practices across England, linked with hospital and mortality records. It forms part of the DIAGNOSE-NP project, supported by the National Institute for Health and Care Research (NIHR) through the Oxford Applied Research Collaboration (ARC) and the Community Healthcare Medtech and In Vitro Diagnostics Cooperative.
What the researchers found
AF and heart failure frequently co-exist and within those assessed in the study, around one in ten people undergoing an NT-proBNP test (17,400) had AF. Additionally, people with AF were more than twice as likely to be diagnosed with heart failure within six months of testing as those without AF (24% compared with 8%).
However, people with AF often had higher NT-proBNP levels even when they did not have heart failure. This is because the irregular, fast rhythm in AF can also raise NT-proBNP levels in the blood above the current threshold to refer for heart failure, which makes it harder to interpret the results.
As a result, the test was less accurate in people with AF. It could still help rule out heart failure when levels were low but this was unusual. The current referral threshold would mean most patients need referring for further testing of heart failure– putting pressure on secondary care services and leading to more false positive results.