What labs should be ordered for a patient with suspected heart failure in the emergency department?

Laboratory Testing for Suspected Heart Failure in the Emergency Department

For a patient with suspected heart failure presenting to the emergency department, you should immediately order: natriuretic peptides (BNP or NT-proBNP), complete blood count, serum electrolytes (sodium, potassium, calcium, magnesium), blood urea nitrogen, creatinine, cardiac troponin, glucose, liver function tests, and thyroid-stimulating hormone. 1

Essential Initial Laboratory Panel

The following tests form the core diagnostic workup and should be obtained at presentation:

Natriuretic Peptides (Priority Test)

• BNP or NT-proBNP measurement is a Class I recommendation for all patients with acute dyspnea and suspected heart failure to differentiate cardiac from non-cardiac causes of dyspnea 1
• Normal levels make heart failure unlikely (thresholds: BNP <100 pg/mL, NT-proBNP <300 pg/mL) 1
• These biomarkers have high sensitivity and can reduce time to discharge and treatment costs 1
• Important caveat: Elevated levels do not automatically confirm heart failure, as they can be elevated in pulmonary embolism, COPD, renal dysfunction, and other conditions 1
• BNP levels tend to be lower in obese patients and may be less elevated in heart failure with preserved ejection fraction 1

Complete Metabolic Assessment

• Serum electrolytes including sodium, potassium, calcium, and magnesium 1

  • Hypokalemia increases risk of fatal arrhythmias and digitalis toxicity 1
  • Hyperkalemia may complicate ACE inhibitor, ARB, or aldosterone antagonist therapy 1
  • Hyponatremia indicates disease progression and impaired survival 1

• Renal function tests: Blood urea nitrogen (BUN) and creatinine 1

  • High BUN (≥43 mg/dL) and creatinine (≥2.75 mg/dL) identify high-risk patients with 22% in-hospital mortality 1
  • Worsening renal function requires medication dose adjustments 1

Cardiac and Metabolic Markers

• Cardiac troponin should be measured in all patients at admission 1

  • Elevated troponin is common in heart failure with increasingly sensitive assays 1
  • Useful for both diagnosis and prognostication, as elevated levels predict poorer outcomes 1

• Glucose (fasting blood glucose or glycohemoglobin) 1

• Liver function tests 1

  • Often impaired due to hemodynamic derangements (reduced cardiac output and venous congestion) 1
  • Abnormal results identify patients at risk for poor prognosis 1

Additional Essential Tests

• Complete blood count 1

  • Development of anemia may signal disease progression and is associated with impaired survival 1

• Thyroid-stimulating hormone (TSH) 1

  • Should be measured routinely, especially in newly diagnosed heart failure 1

• Lipid profile 1

• Urinalysis 1

Monitoring During ED Stay and Hospitalization

• Renal function and electrolytes should be measured daily during hospitalization 1
• Creatinine, BUN, and electrolytes should be checked every 1-2 days while hospitalized and before discharge 1
• More frequent testing may be justified based on severity 1

Common Pitfalls to Avoid

1. Do not rely solely on natriuretic peptides for diagnosis—they should be used in combination with clinical evaluation, not in isolation 1
2. Interpret BNP/NT-proBNP cautiously in women and patients over 60 years old, as levels may be meaningfully elevated without heart failure 1
3. Remember obesity lowers natriuretic peptide levels, which can lead to false reassurance 1
4. Unexpectedly low natriuretic peptides can occur in decompensated end-stage heart failure, flash pulmonary edema, or right-sided heart failure 1
5. Serial potassium monitoring is critical as hypokalemia from diuretics can cause fatal arrhythmias 1