Pulmonary edema laboratory tests

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Farnaz Khalighinejad, MD [2]

Overview

Laboratory findings consistent with the diagnosis of pulmonary edema include hypoxia, hypercapnia, acidosis. Elevated B-type natriuretic peptide (BNP) and cardiac enzyme is usually suggestive of cardiogenic pulmonary edema.

Laboratory Findings

Laboratory findings consistent with the diagnosis of pulmonary edema include:

Arterial blood gas test:

• Hypoxia:
  • Oxygen saturation < 90%
  • PaO2 < 60 mm Hg

• Hypercapnia:
  • CO2 > 45–55 mm Hg

• Acidosis:
  • PH < 7.35 nEq/liter
  • Early findings of pulmonary edema may be respiratory alkalosis because of hyperventilation

Serum albumin:

• Albumin may be low in pulmonary edema

Liver function tests:

• Elevation in alanine aminotransferase, aspartate aminotransferase and bilirubin may be seen in right ventricular failure as underlying cause of cardiogenic pulmonary edema

Plasma brain natriuretic peptide levels :

• B-type natriuretic peptide (BNP) is elevated in the patient with cardiogenic pulmonary edema.

• A low BNP (<100 pg/ml) makes a cardiac cause very unlikely and is associated with non-cardiogenic pulmonary edema.

Pulmonary capillary wedge pressure(PCWP):

• A wedge pressure of 18 mmHg or higher is usually suggestive of cardiogenic pulmonary edema.
• A wedge pressure of less than 18 mmHg is usually suggestive of non-cardiogenic pulmonary edema.

Cardiac enzymes:

• Elevated concentration of troponin, may suggestive of damage to myocytes, as underlying cause of cardiogenic pulmonary edema.

Shunt fractions (Qs/Qt):

• Patients with non-cardiogenic pulmonary edema had greater shunt fractions(Qs/Qt) than patients with cardiogenic pulmonary edema.

Differentiation of cardiogenic pulmonary edema and noncardiogenic pulmonary edema

Laboratory findings	Cardiac enzymes	BNP	PCWP	QS/QT
Cardiogenic pulmonary edema	May be elevated	High	>18 mmHg	Small elevated
Noncardiogenic pulmonary edema	Usually normal	Low	<18 mmHg	Large elevated