Using BNP to Diagnose Heart Failure

Question 1

What is BNP?

Answer 1

Brain Natriuretic Peptide

• A hormone released predominantly from the ventricles when they are stretched beyond normal parameters due to pressure or volume overload
• BNP causes the renal tubules to increase excretion of Na+ and H20 which reduces plasma volume and reduces ventricular wall stress.
• BNP has an inactive precursor: NTproBNP

Question 2

How is BNP relevant to heart failure?

Answer 2

In heart failure ventricles aren’t able to pump effectively so become stretched which causes release of BNP.
BNP is shown to increase with NYHA classification so BNP level appears to correspond with severity of HF

Question 3

What are the problems with using BNP?

Answer 3

Lots of factors can cause BNP to rise:

• Age
• RV overload
• Ischaemoa
• Tachycardia
• Hypoxaemia
• Sepsis
• P.E
• COPD
• Pregnancy

Question 4

How is BNP used in heart failure?

Answer 4

Cowie et al, 1997:
It was noted that BNP was significantly increased in Heart failure, so could this be utilised for diagnostic purposes.
the FIRST study to investigate diagnostic utility
-small trial of 100 patients
-found that mean concentrations of BNP were significantly higher in patients with confirmed heart failure and had high sensitivity and specificity
*ANP was also assessed but did not show the same high results
*Led to a bigger trial of BNP use

Question 5

What is the key trial used for BNP use in heart failure?

Answer 5

UK Natriuretic Peptide Study, 2005

Question 6

Methods of UK Natriuretic Peptide Study:

Answer 6

• 300 patients from 5 rapid access clinics
• blood samples, CXR, ECG, ECHO
• Used BNP cut off points recommended by the manufacturuer: BNP <100pg/ml, NTproBNP <125pg/ml

Question 7

UK Natriuretic Peptide Study Outcomes:

Answer 7

BNP was significantly higher in ECHO confirmed Heart failure
At manufacturers cut off points, NTproBNP had a higher negative predictive value so was good at ruling heart failure OUT
But BNP had a high positive predictive value so was good at ruling heart failure IN
-Comparison with ECG showed there was no diagnostic difference between the two

Question 8

BNP Systematic Review

Answer 8

Mant et al, 2009:
Assessment of diagnostic tools in Heart failure using 155 studies
-BNP and NTproBNP had the highest sensitivity and Youden Index (measure of diagnostic accuracy)
-Showed there was no difference between BNP and NTproBNP so trusts can choose at their discretion depending on cost
-Showed that if ECG is unavailable, BNP is just as useful

Question 9

What about the BNP cut offs?

Answer 9

at the mentioned exclusionary cut offs:
-negative predictive values are high
-positive predictive values are low
So these cut offs are recommended for ruling OUT heart failure but not to establish the diagnosis
-There is no specific evidence for what the cut off points should be-these are arbitrary based on heart failure severity