B-type natriuretic peptide (BNP) levels are elevated in congestive heart failure as well as other conditions that increase wall tension in the cardiac ventricles. A level of 100 pg/ml has been suggested as diagnostic of congestive heart failure (CHF).
LB, a 55 year old African American woman, was admitted from the emergency department with dyspnea and hypoxia. Oxygen saturation was 78% on room air and increased to 92% on 4L/min supplemental oxygen. Her past medical history is significant for emphysema with continued tobacco abuse and coronary artery disease with recent (2 months ago) 4 vessel bypass surgery. She was re-admitted 1 month later with congestive heart failure (CHF) and left ventricular ejection fraction (LVEF) was documented to be 45% by transthoracic echocardiogram (TTE). Physical exam revealed bilateral ronchi with no S3, S4, or other signs of congestive heart failure. Chest x-ray revealed diffuse pulmonary infiltrates, BNP was 2450 pg/ml. She was admitted to a telemetry unit and aggressively diuresed with intravenous furosemide. Over 5 days her weight dropped to 105.5 from 122.8 pounds at admission, and serum creatinine increased from 2.1 to 2.5 mg/dl. Repeat BNP was 1830 pg/ml. Nesiritide infusion was begun and continued for 72 hours, with continued diuresis of approximately 2 liters daily net negative fluid balance. The patient remained hypoxic, requiring 50 percent oxygen by face mask to maintain oxygen saturations greater than 90 percent. Repeat TTE revealed an LVEF of 65%. A third BNP level was 674 pg/ml. Chest Computed Tomography (CT) was obtained due to persistent pulmonary infiltrates on chest radiographs. This revealed extensive honeycombing with severe bullous disease and infiltration of the remaining lung parenchyma as well as a discrete mass in the left upper lobe. This result was not felt to rule out concurrent CHF, so to definitively assess cardiac output, volume status and left ventricular filling pressure, a right heart catheterization was performed. Pulmonary artery pressure was 22/10 mmHg, pulmonary capillary wedge pressure was 2 mmHg, and cardiac output was 4.5 liters per minute. Open lung biopsy was then performed, revealing interstitial fibrosis, bronchial and squamous metaplasia, and extensive honeycomb lung consistent with idiopathic pulmonary fibrosis. Oral corticosteroid therapy was begun with poor results.DISCUSSION: BNP is a very useful test that has been extensively studied. It can aid in the correct diagnosis of CHF in those patients who remain undiagnosed after clinical evaluation. Levels of BNP are elevated in diastolic as well as systolic cardiac dysfunction. Pulmonary causes have also been shown to be associated with elevated BNP, but to a lesser degree than decompensated LV failure.CONCLUSIONS: Laboratory tests serve to confirm clinical diagnoses made by thoughtful history taking and careful physical examination, or to help with difficult cases. Laboratory tests such as BNP may be misleading if not taken in clinical context, delaying correct diagnosis and treatment. There has been much enthusiasm regarding the diagnostic utilities of BNP. This is very useful test, but should be used in a specific clinical context to answer a specific question, not as a replacement for the history and physical.
D.M. Safley, None.