BNP (B-type Natriuretic Peptide) is the Most Highly Diagnostic Test
In an elderly patient presenting with sudden severe chest pain, orthopnea, and bilateral lung crepitations with normal sinus rhythm on ECG, BNP is the most highly diagnostic test to confirm acute heart failure syndrome. This clinical presentation—orthopnea plus bilateral crackles—strongly suggests acute decompensated heart failure rather than acute coronary syndrome, making BNP the priority diagnostic test 1.
Clinical Reasoning
Why BNP Over Other Tests
BNP demonstrates superior diagnostic accuracy for acute heart failure in patients presenting with dyspnea and signs of pulmonary congestion. The evidence shows:
- BNP at a cut point of 100 pg/mL has 96% sensitivity and 61% specificity for heart failure diagnosis 1
- At 295 pg/mL, BNP achieves 80% sensitivity with 86% specificity, with an area under the curve of 0.92 1
- In elderly patients (>65 years) with acute dyspnea, BNP at 250 pg/mL demonstrates 73% sensitivity and 91% specificity 1
Why Not Troponin in This Case
While troponin is essential for acute coronary syndrome evaluation, this patient's presentation is dominated by heart failure symptoms (orthopnea, bilateral crackles) rather than ischemic chest pain 2. The ECG shows normal sinus rhythm without ST-segment elevation, making STEMI unlikely 1, 2. Troponin would be indicated if the chest pain characteristics suggested acute coronary syndrome with radiation to arm/jaw, or if ECG showed ischemic changes 1.
Why Not D-dimer
D-dimer is primarily useful for pulmonary embolism evaluation 3. This patient's bilateral lung findings and orthopnea point to cardiogenic pulmonary edema, not thromboembolic disease 1. Pulmonary embolism typically presents with acute dyspnea and unilateral findings, not bilateral crackles with orthopnea 3, 4.
Diagnostic Algorithm for This Presentation
Immediate Assessment (First 10 Minutes)
- Obtain 12-lead ECG to exclude STEMI and assess for arrhythmias 2
- Draw BNP immediately upon presentation 1
- Perform focused cardiovascular examination for heart failure signs: elevated JVP, S3 gallop, peripheral edema 2
BNP Interpretation in Elderly Patients
Age-adjusted cut points are critical in elderly patients 1:
- For age <75 years: BNP >125 pg/mL suggests heart failure 1
- For age ≥75 years: BNP >450 pg/mL is the appropriate threshold 1
- NT-proBNP can be used alternatively with age-stratified cut points 1
Complementary Testing
Once BNP confirms heart failure:
- Transthoracic echocardiography should be performed to assess ejection fraction, valve function, and wall motion abnormalities 1, 5
- Chest radiograph evaluates for pulmonary venous congestion and cardiomegaly 1, 2
- Troponin should still be measured to identify concurrent acute coronary syndrome, as 20-30% of acute heart failure patients have concomitant myocardial injury 1, 2
Critical Pitfalls to Avoid
Do not dismiss cardiac causes in elderly patients with atypical presentations. Elderly patients frequently present with dyspnea, fatigue, or confusion rather than classic chest pain 2. The combination of orthopnea and bilateral crackles has high specificity for acute heart failure 1.
Do not delay BNP testing while waiting for troponin results. In patients with clear heart failure symptoms, BNP provides immediate diagnostic clarity 1. BNP combined with clinical assessment achieves diagnostic accuracy superior to clinical judgment alone (AUC 0.93 vs 0.86) 1.
Do not use a single BNP cut point across all ages. The evidence demonstrates that age-stratified thresholds significantly improve diagnostic accuracy in elderly patients 1. Using the standard 100 pg/mL cut point in a 75-year-old would result in excessive false positives 1.