Diagnostic Use
BNP is a 32 amino acid hormone secreted from cardiac myocytes subjected to increased ventricular wall stress. NT-proBNP is the inactive cleavage product of the secretion of BNP, and is used as a marker of BNP. Its half life is approximately 40 minutes, compared with a half-life of approximately 20 minutes for active BNP.
Interpretation
BNP is a 32 amino acid hormone secreted from cardiac myocytes due to increased ventricular wall stress. It is the active cleavage product of proBNP, NT-proBNP being the inactive product. Its half life is approximately 20 minutes, compared with a half-life of approximately 40 minutes for NT-proBNP. Its level correlates with the degree of left ventricular dysfunction and with the severity of heart failure based on the New York Heart Association (NYHA) criteria. BNP levels can also rise in non-cardiac pathologies.
Causes of elevated BNP
A)Cardiac:
Congestive Heart Failure:
Acute Coronary Syndromes:
Left Ventricular Hypertrophy:
Hypertrophic & Restrictive Cardiomyopathy:
Constrictive Pericarditis:
Valvular Heart Disease :
Atrial Fibrillation:
Supraventricular tachycardia:
B)Non Cardiac::
COPD:
Pulmonary Embolism & Pulmonary Hypertension :
Sepsis:
Hypertension:
Subarachnoid Haemorrhage:
Renal Failure:
Levels in health and disease can be affected by:
Age — increasing with increasing age
Gender — slightly higher in females
BMI — levels are lower with increasing BMI.
Race — levels are higher in Caucasians compared to African Americans
Clinical Use:
Heart Failure
BNP measurement is useful for excluding heart failure.
Monitoring
Levels drop with improvement in cardiac function. A drop of at least 30% after treatment can be associated with better outcome.
Prognostication and outcome measurement
BNP was found to be an independent predictor of morbidity and mortality in patients with CHF .An increase of 30 pmol/L was associated with approximately 35% relative increased risk of death Independent predictor of LV dysfunction and death in patients with ACS Predictor of overall mortality in ICU patients.
Biological variation
High. Changes of 113-130% are needed for reliable clinical interpretation.
Different Clinical Settings
Sepsis
BNP is found to have limited clinical usefulness in septic patients so far; it does not reliably correlate with cardiac function or filling pressures. At low levels only, it may aide rule out cardiogenic shock.
Renal Failure
BNP is less affected by decreasing glomerular function than NT-proBNP, with or without CHF. Nevertheless, levels do rise with falling GFR. A level of < 60 pmol/L is suggested to rule out CHF in patients with eGFR <60mL/min/1.73m3
R.I:
a) ED patient with dyspnoea/History of CHF/high pre-test probability
>/= 30 pmol/L probably has CHF
>/= 16 pmol/L if BMI>/=35 probably has CHF
< 14 pmol/L probably does not have CHF
b) No history of CHF/low pre-test probability
< 40 pmol/L probably does not have CHF
< 46 pmol/L if age >/=73 yrs probably does not have CHF
BNP should not be used in isolation for the diagnosis or exclusion of Heart Failure.
Unit conversion:
ng/L x 0.289 = pmol/L
Uncertainty of Measurement
At a level of 24 pmol/L - 17%
At a level of 960 pmol/L - 11%