We doctors love to order tests, often only to confirm things we already know. Did that lactate level for the child in SHOCK help your decision to start vasopressors? Better yet, did that WBC count really help us determine whether the child with fever has a bacterial infection? Yet, there are times when our clinical assessment can still leave us struggling to decide between two significant entities: like respiratory distress due to heart failure or pulmonary disease. In adults, we often us the B-Type Natriuretic Peptide (BNP) to help us distinguish between these two issues, but can we use the BNP in children? Let us review the BNP use in children:

BNP: Basics

• B-Type Natriuretic Peptide (BNP): [Neves, 2016]
  • Is derived from proBNP which is cleaved into biologically inactive NT-proBNP and proBNP (typically referred to as BNP), which is biologically active.
  • Has a half life of 15-20 min (versus NT-proBNP with half life of 1-2 hours)
  • Testing results vary between different immunoassay methods.

• The active segment of BNP: [Neves, 2016]
  • Has natriuretic, vasodilatory, and diuretic effects.
  • Counteracts the renin-angiotensin-aldosterone and sympathetic nervous systems.

• BNP is released from ventricular myocardium in response to wall stress due conditions that lead to: [Neves, 2016]
  • Increased Preload
  • Increased Afterload
  • Decreased Systolic Ventricular Function
  • Decreased Diastolic Ventricular Function

• While we often think of BNP as being related to heart failure, it can be elevated for a variety of reasons, including:
  • Liver failure
  • Renal impairment (although, BNP can still serve as a marker of heart strain in these patients) [Rinat, 2012]
  • Hemodynamically significant pulmonary emboli
  • Cor pulmonale
  • Inflammatory diseases

BNP: Age Matters

BNP / NT-proBNP levels are influenced by the patient’s age (come on people, it’s pediatrics… of course the age matters)

• In the ED, if there is clinical suspicion for cardiovascular disease, the current described discriminatory levels are: [Cantinotti, 2014; Law, 2009; Maher, 2008]
  • For 1st week of life – cutoff of 170 pg/mL (Sen- 94%; Spec- 73%)
  • Older infants and children (up to 19 years) – cutoff of 41 pg/mL (Sen- 87%; Spec- 70%)
  • Below the discriminatory level, the presentation is not likely related to cardiovascular etiology (thus, more likely related to something like Bronchiolitis). [Maher, 2008]

• Levels are most elevated in the first 3-4 days of life: [Neves, 2016; Cantinotti, 2014; Law, 2009; Maher, 2008]
  • Potentially to help with natriuresis and reduction of pulmonary vascular resistance.
  • Additionally, kidneys are more immature and after load increases.
• Levels fall throughout first month of life. [Neves, 2016; Cantinotti, 2014]
• From 1 month of age to ~12 years of age, BNP levels remain relatively stable in healthy individuals. [Neves, 2016; Cantinotti, 2014]
• After puberty, levels can increase toward adult levels and are higher in females than males. [Neves, 2016]

BNP: Uses in Children

Diagnosis of newly developed heart failure in children is very challenging as it often initially presents with subtle and non-specific findings.

• BNP / NT-proBNP levels, in the clinical setting of suspicion for possible heart failure, have been shown to be valuable.
  • Improves the diagnostic accuracy in the evaluation of heart disease in children. [Neves, 2016; Cantinotti, 2014; Maher, 2008]
  • Increase the accuracy of neonatal screening for Congenital Heart Disease. [Neves, 2016; Cantinotti, 2014]

• BNP / NT-proBNP levels can also be used to evaluate patients with known heart failure and monitor the effectiveness of therapies and need for surgery. [Neves, 2016; Cantinotti, 2015; Cantinotti, 2014; Auerbach, 2010]
• BNP levels need to be assessed based on specific commercial assay (cannot compare different assays’ levels). NT-proBNP measurements are not affected by different assays though. [Cantinotti, 2014]
• NT-proBNP might be an adjunctive marker for hyper-acute phase of Kawasaki Disease. [Kwon, 2016]

Moral of the Morsel

• Are you sure it’s bronchiolitis? Is that liver enlarged? Clinical concern for CHF? Check a BNP.
• Know that the BNP levels need to be assessed based on the patient’s age. Don’t use the adult cutoffs.

References