Why is LDH elevated in pleural fluid from Diuretics: Mechanism
It is common teaching to be judicious when interpreting the thoracentesis results of patients receiving diuretic therapy. It is stated, their pleural LDH will often be elevated and result in them being misclassified as exudative effusions when they are in fact transudative.
Currently, the mechanism is not entirely clear, but proposed mechanisms include:
Lactate dehydrogenase (LDH) is an intracellular protein responsible for catalysing the conversion of lactate to pyruvic acid. It tends to leak during cellular injury or lysis.
Thus, any patient with repeated or bloody thoracentesis, the LDH may be elevated secondary to RBC lysis (blood) or local trauma from the thoracentesis; repeated attempts augmenting that damage.
LDH is primarily created by the liver, and in patients with CHF, hepatic congestion/ release upon diuresis may play a role in its elevation in pleural fluid.
Diuretics move water via diffusion; from the extravascular (pleural space) to the blood, leading to an increase in the protein and LDH concentration in the pleural cavity.
Bielsa, J.M. Porcel, J. Castellote, et al. Solving the Light’s criteria misclassification rate of cardiac and hepatic transudates. Respirology, 17 (2012), pp. 721-726
Mitrouska I, Bouros D. The Trans-Exudative Pleural Effusion. CHEST, Volume 122, Issue 5, 1503 – 1505
Broaddus, V. Diuresis and transudative effusions—changing the rules of the game. The American Journal of Medicine, Volume 110 , Issue 9 , 732 – 735