Diagnosis of heart failure

NT-proBNP testing

Blood testing for B-Type Natriuretic Peptide (BNP) is a key step in the diagnostic pathway for heart failure. This is now recommended by NICE as the first investigation when heart failure is suspected on clinical grounds.

N-Terminal B-Type Natriuretic Peptide (NT-proBNP) testing is now available to all GPs in the region via the OUH FT pathology labs and has (as of 6 November 2019) replaced the previously used assay. The normal and abnormal ranges are different. Unlike BNP, NT-pro BNP is not subject to the issue of degradation with falsely low readings if the sample is delayed in transit. Nonetheless, samples need to reach the lab within 24h. Please send a serum sample (gold/yellow top tube).

NT-proBNP pitfalls:

• NT-proBNP is a test for heart failure and a low level does not exclude significant cardiac disease of other sorts. Patients could have a low NT-proBNP and other cardiac pathology such as valvular heart disease, coronary disease, or hypertensive heart disease (although are unlikely to have heart failure due to the above).
• NT-proBNP is not specific for heart failure, and there are many other causes of high BNP levels including hypoxaemia, renal dysfunction, sepsis, chronic obstructive pulmonary disease, diabetes, and cirrhosis.
• A small number of patients can have significant heart failure despite a low BNP level. We are happy to discuss (or see) these patients if you are concerned that this may be the case. In this context an ECG in the community can be helpful (heart failure is very unlikely with a low BNP and normal ECG).
• NICE have selected the cut-off level of 400ng/L to provide a relatively high specificity. Age related cut-offs can improve sensitivity:
  • In patients less than 50 years of age, NT-proBNP less than 50ng/L provides a very high sensitivity to rule out heart failure
  • In patients 50-75 years of age, NT-proBNP less than 75ng/L provides high sensitivity
  • In patients over 75 years, use of the 400ng/L cut off is adequate
• Patients who are already known to have heart failure and are on heart failure medications may have a low BNP despite significant heart failure. If you are concerned about a deterioration in a patient with an existing diagnosis of heart failure, please discuss with or refer to the heart failure team regardless of the BNP.
• Similarly, if patients are already on ACE inhibitors, Angiotensin receptor blockers, or diuretics then BNP may be lower due to partial treatment of the heart failure
• African & Afro-Caribbean patients may have lower levels of BNP
• Obesity may reduce BNP levels

Management while waiting for appointment

Investigations prior to clinic

It is very helpful for us to have some additional investigations performed prior or at the time of referral, so the results are available at the time of the clinic visit:

• FBC        To check for anaemia as a contributor to symptoms
• C&E       To help guide & monitor use of ACE inhibitors/diuretics, and exclude renal dysfunction
• LFT         To exclude liver dysfunction as a cause of oedema, and assess for hepatic congestion
• TFT         If not done within the last 6 months

Routine testing of lipids & HbA1c prior to referral is not generally useful unless there is a particular reason to suspect diabetes or dyslipidaemia.

ECG prior to referral is required please, and will be helpful for your own management of the patient prior to their clinic visit, especially if there is clinical suspicion of atrial fibrillation

Routine CXR is not required unless there is clinical suspicion of significant respiratory disease.

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Treatment prior to clinic

Fluid Overload

If the patient has clinical evidence of fluid overload, then early treatment with diuretics can be transformative and help prevent acute admission. Signs of fluid overload include peripheral oedema, ascites, and elevated JVP, as well as orthopnoea and paroxysmal nocturnal dyspnoea.

In ‘diuretic naïve’ patients with satisfactory renal function a dose of 40mg od furosemide is generally a reasonable starting point.

Atrial Fibrillation

Atrial fibrillation is often present in patients with heart failure. If this is confirmed on ECG, then rate control with either beta blockade or digoxin can be used if heart rate >100. Assessment for anticoagulation according to standard guidelines should be undertaken alongside heart failure clinic referral, and we would suggest anticoagulation is started in the community.

Others

Other heart failure medications should not generally be initiated until the patient has been seen in the clinic and had an echo performed, so that we know whether this is heart failure with a reduced or preserved ejection fraction.

Treatment protocols for heart failure with reduced and preserved ejection fraction are detailed here

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