Laboratory Testing for Congestive Heart Failure
BNP (B-type natriuretic peptide) or NT-proBNP (N-terminal pro-B-type natriuretic peptide) is the primary laboratory test used to diagnose congestive heart failure. 1, 2
Diagnostic Cut-offs in the Acute Setting
When evaluating patients presenting with acute dyspnea in the emergency department:
- BNP < 100 pg/mL effectively rules out heart failure with 90% sensitivity, 76% specificity, and 81% diagnostic accuracy 1, 2, 3
- BNP > 400 pg/mL strongly indicates heart failure as most patients with significant CHF have levels above this threshold 4, 5
- BNP 100-400 pg/mL represents a "gray zone" requiring further evaluation to exclude left ventricular dysfunction without volume overload, pulmonary embolism, or cor pulmonale 1, 4
For NT-proBNP testing in acute presentations:
- Age < 50 years: Use 450 pg/mL as the cut-off 1, 2
- Age ≥ 50 years: Use 900 pg/mL as the cut-off 1, 2
- NT-proBNP has 99% negative predictive value for ruling out acute heart failure 1
Non-Acute/Ambulatory Setting
In the outpatient setting, natriuretic peptide testing has different characteristics:
- Lower cut-offs may apply as chronically stable heart failure patients can have BNP levels below the acute diagnostic threshold of 100 pg/mL 1
- BNP/NT-proBNP testing helps exclude heart failure when the diagnosis is uncertain (Class IIa recommendation) 1, 2
- A completely normal ECG makes heart failure unlikely (<10% probability), reducing the need for natriuretic peptide testing 1
Essential Complementary Laboratory Tests
Beyond natriuretic peptides, the following tests are recommended for initial heart failure evaluation:
Routine blood work (Class I recommendation): 1
- Complete blood count (hemoglobin, white blood cells)
- Serum electrolytes (sodium, potassium)
- Renal function (creatinine with estimated GFR, blood urea nitrogen)
- Liver function tests (bilirubin, AST, ALT, GGTP)
- Glucose and HbA1c
- Thyroid-stimulating hormone (TSH)
- Ferritin and transferrin saturation (TSAT)
12-lead ECG is mandatory to determine rhythm, heart rate, QRS morphology and duration 1
Chest X-ray is essential to detect pulmonary congestion, cardiomegaly, pleural effusions, and exclude alternative pulmonary causes of dyspnea 1
Critical Factors Affecting BNP Interpretation
Several clinical conditions significantly influence natriuretic peptide levels and must be considered:
Factors causing falsely low BNP: 1, 2
- Obesity (most important confounder—interpret with extreme caution in obese patients)
Factors causing elevated BNP without heart failure: 1, 6
- Advanced age and female sex
- Renal dysfunction (both BNP and NT-proBNP are renally cleared)
- Atrial fibrillation
- Pulmonary hypertension, pulmonary embolism, COPD
- Diastolic dysfunction
- Mitral regurgitation
- Right ventricular dysfunction
- Recent cardiac surgery
- Acute coronary syndromes
Clinical Implementation Algorithm
Patient presents with dyspnea → Obtain BNP or NT-proBNP 1
If BNP < 100 pg/mL (or NT-proBNP < 400 pg/mL) → Heart failure highly unlikely; consider alternative diagnoses 1, 2
If BNP 100-400 pg/mL → Uncertain diagnosis; proceed to echocardiography and evaluate for confounding factors 1, 4
If BNP > 400 pg/mL (or NT-proBNP > 2000 pg/mL in chronic setting) → Heart failure likely; obtain echocardiography and complete laboratory evaluation 1, 2
Important Clinical Pitfalls
Never use BNP as a stand-alone test—it must be interpreted within the full clinical context including history, physical examination, ECG, and chest X-ray 1
Do not use BNP to replace echocardiography—natriuretic peptides confirm or exclude the diagnosis, but echocardiography is required to assess left ventricular structure, function, and ejection fraction (Class III recommendation against using BNP as replacement) 1
Avoid routine BNP testing in obvious heart failure—when the clinical diagnosis is clear from history and physical examination, natriuretic peptide testing adds no value (Class III recommendation) 1
BNP and NT-proBNP are not interchangeable—there is no direct conversion between assays due to differences in half-lives, clearance, and production, though their diagnostic and prognostic abilities are comparable 1, 2