Correct!
4. Elevated adenosine deaminase in the pleural fluid is diagnostic of heart failure
Transudates are characterized by low pleural fluid protein (<0.5 compared to serum) and a low LDH (pleural fluid LDH/serum LDH level < 0.6, or pleural fluid LDH level < 2/3 the upper normal limit for serum LDH) (4). These are known as the Light criteria. The patient’s serum LDH was 210 IU/L and so the effusion is consistent with a transudate. The primary problem with the Light criteria is that they identify 15% to 20% of effusions secondary to heart failure as exudative effusions. This situation is particularly likely if the patient has been receiving diuretics before the thoracentesis. If tuberculous pleuritis is suspected, a pleural fluid ADA level should be obtained. Pleural fluid ADA levels more than 40 U/L in a patient with predominantly lymphocytes in their pleural fluid are virtually diagnostic of tuberculous pleuritis (4). ADA levels are normal in heart failure. Pleural fluid glucose is usually normal in heart failure (4).
The most common cause of bilateral transudative effusions is heart failure (4). However, the patient’s normal heart size, normal systolic function on echocardiogram and the low NT-pro BNP suggest another source.
Which of the following causes of heart failure is best associated with clinical heart failure but a normal heart size, normal systolic function on echocardiogram and a low NT-pro BNP?