Chest
Volume 98, Issue 3, September 1990, Pages 546-549
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Clinical Investigations
The Serum-Effusion Albumin Gradient in the Evaluation of Pleural Effusions

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The objective of the study was to compare the serum-effusion albumin gradient (serum albumin level minus pleural effusion albumin level) to Light's traditional criteria (pleural fluid/serum total protein ratio > 0.5, pleural fluid/serum LDH ratio > 0.6, and pleural fluid LDH > 200 U/L) for identifying exudative pleural effusions. The design included prospective measurement of the serum-effusion albumin gradient and Light's criteria in patients with pleural effusions in an inpatient ward in a military teaching hospital. Fifty-nine consecutive patients with pleural effusions who were undergoing diagnostic or therapeutic thoracentesis in whom the etiology of the effusion could be determined were studied. Serum and pleural effusion fluid chemistries were measured in order to determine both the serum-effusion albumin gradient and Light's criteria. Using an albumin gradient of 1.2 g/dl or less to indicate exudates and greater than 1.2 g/dl to indicate transudates, 57 of the 59 patients (41 exudates; 18 transudates) were correctly classified. Two patients with malignant effusions were misclassified as having transudates. Although Light's criteria correctly identified all of the exudates, five patients with congestive heart failure were misclassified as exudates. Four of these patients had had previous diuretic therapy, and all had a clinical response to further diuretic therapy. We conclude that although Light's criteria for exudates are very sensitive, an albumin gradient of 1.2 g/dl or less tends to be more specific, especially in cases of chronic congestive heart failure.

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MATERIALS AND METHODS

The subjects were adult consecutive inpatients from the general medicine service or intensive care unit at Madigan Army Medical Center who had a diagnostic or therapeutic thoracentesis performed between June 1988 and April 1989. The protocol was accepted by the local human utilization review committee. All patients signed a consent form to participate in the study.

The following studies were performed on all pleural fluid samples: albumin; glucose; protein; LDH; cell count; differential cell

RESULTS

Sixty-one patients with pleural effusions were evaluated. One patient was excluded due to the diagnosis of empyema. Another patient was excluded because a simultaneous serum sample was not obtained. Of the 59 remaining patients, 37 were men, and 22 were women. The average age was 61 years (range, 19 to 84 years). Forty-one were defined as having exudates and 18 as transudates. In all cases the diagnosis reached after chart review was the same as that given by the primary physicians. The

DISCUSSION

Despite being studied for over 100 years, the physiology of pleural fluid formation and absorption is still controversial. The most recent accepted model of pleural fluid exchange in the normal state involves formation by filtration through the pleural microvascular endothelium and absorption via stomata in the parietal pleura that drain into subpleural lymphatic vessels. The formation of fluid is powered by the pressure gradient between the microvasculature and pleural space, while absorption

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The opinions and assertions contained herein are the private views of the authors and do not necessarily reflect the views of the Department of Defense.

Manuscript received October 19; revision accepted February 13.

Reprint requests: Dr. Roth, Department of Clinical Investigation, Box 454, Madigan Army Medical Center, Tacoma, WN 98431-5454

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