Though traditional cutoffs for protein levels and LDH values were reported in the 1970s to reliably distinguish between exudates and transudates, more recent ROC analyses have questioned this assumption. The purpose of this study was to determine the incidence of pleural effusions that were exudative by either protein or LDH and transudative by traditional cutoff values. Further, we wanted to identify specific diagnoses which occurred within the dysynchronous groups.
A database has been collected of all pleural procedures performed at the Medical University of South Carolina for safety purposes. We retrospectively examined this data from July 2001 to October 2004. We included all initial thoracenteses provided that the pleural protein, LDH, and serum protein values were obtained. We defined an exudate by protein as a pleural fluid/protein ratio of ≥.51 and by LDH as an LDH value of ≥161 (2/3 of our upper limits of normal). We classified effusions as synchronous exudates, synchronous transudates, dysynchronous effusions with elevated protein ratios only, and dysynchronous effusions with elevated LDH levels only. We then reviewed all available clinical data and assigned diagnoses to the effusions.
Table 1 shows the characteristics of these 211 effusions that met criteria for study.
Pleural fluid dysynchrony was found in 39% of effusions. The most common causes were parapneumonic, paramalignant, and malignant, effusions. Trapped lung, entrapped lung, chylothorax and post-liver transplant effusions were dysynchronous effusions with high protein ratios and low LDH levels; these processes are characterized by minimal inflammation with abnormal pleural lymphatics. The high incidence of dysynchronous pleural effusions confirms that isolated values in the pleural fluid analysis are not consistently reliable diagnostically.
Pleural fluid analysis must be used in conjunction with the clinical presentation in determining the cause of a pleural effusion. Pleural fluid dysynchrony can indicate whether an exudative effusion is primarily due to a lymphatic abnormality with elevated protein or to inflammation (increased LDH). Traditional transudates, like CHF, rarely cause pleural fluid dysynchrony except following intense diuresis.
Jay Heidecker, None.DiagnosisDysynchronous-high proteinDysynchronous-high LDHTotal n=211 Synchronous transudates n=73 Synchronous exudates n=79 Dysynchronous n=59Parapneumonic (13)58Paramalignant (12)84Malignant (9)72Ideopathic (7)52CHF (4)31Post liver transplant (3)30Chylothorax (2)20Trapped lung (2)20Entrapped lung (2)20Post cardiac surgery (2)02Tuberculosis (2)02Acute pancreatitis (2)01Total3722