What initial lab orders are recommended for a patient admitted with dyspnea, leg swelling, and a history of pedal edema, with an X-ray indicating pneumonia?

Laboratory Tests for Patient with Dyspnea, Leg Swelling, and Suspected Pneumonia

For a patient presenting with dyspnea, leg swelling, history of pedal edema, and X-ray findings suggestive of pneumonia, you should order comprehensive laboratory tests to evaluate both cardiac and pulmonary etiologies, with BNP/NT-proBNP being the most critical test to differentiate heart failure from pneumonia. 1

Core Laboratory Tests

• Complete Blood Count (CBC) with differential to assess for leukocytosis (indicating infection) or anemia (which can exacerbate dyspnea) 1, 2
• Basic Metabolic Panel (BMP) to evaluate electrolytes, kidney function (creatinine, BUN), and glucose 1
• Liver Function Tests (LFTs) to assess for hepatic congestion that may occur with right heart failure 1
• Natriuretic Peptides (BNP or NT-proBNP) - critical for differentiating heart failure from other causes of dyspnea; low levels (<40 pg/mL for BNP or <150 pg/mg for NT-proBNP) make left ventricular failure unlikely 1
• C-Reactive Protein (CRP) to assess inflammation; levels >100 mg/L suggest pneumonia, while levels <20 mg/L with symptoms >24 hours make pneumonia unlikely 1
• Arterial Blood Gas (ABG) or Pulse Oximetry to evaluate respiratory status and acid-base balance 1

Cardiac Evaluation

• Troponin to rule out myocardial injury, especially important in patients with risk factors for coronary artery disease 1
• ECG to assess for arrhythmias or ischemic changes that may contribute to heart failure 1

Microbiological Tests

• Blood Cultures (two sets) before antibiotic administration if moderate to severe illness is suspected 1
• Sputum Gram Stain and Culture if the patient can produce adequate sputum sample 1, 2
• Legionella and Pneumococcal Urinary Antigen Tests if pneumonia appears severe or atypical features are present 1

Additional Considerations

• D-dimer if pulmonary embolism is in the differential diagnosis, particularly in patients with risk factors 1
• Procalcitonin (PCT) may help distinguish bacterial from viral pneumonia and guide antibiotic therapy decisions 1, 2

Interpretation and Clinical Correlation

The combination of elevated BNP/NT-proBNP with bilateral pedal edema strongly suggests heart failure, while elevated inflammatory markers with focal chest X-ray findings point toward pneumonia 1. However, these conditions frequently coexist, with pneumonia potentially triggering heart failure exacerbation or vice versa 1.

Common Pitfalls to Avoid

• Failing to check BNP/NT-proBNP - this is essential for differentiating between cardiac and pulmonary causes of dyspnea 1
• Relying solely on chest X-ray - nearly 20% of patients with heart failure may have normal chest X-rays 1
• Not considering dual pathology - patients often have both pneumonia and heart failure simultaneously 1, 3
• Overlooking renal function - worsening kidney function can be both a cause and consequence of heart failure and affects medication dosing 1

Remember that laboratory results must be interpreted in the context of the patient's clinical presentation, as no single test definitively distinguishes between heart failure and pneumonia 1, 2.