Hypoalbuminemia as a cause of pleural effusions

Alterations in Starling forces that favor pleural fluid formation include an elevation in capillary hydrostatic pressure and a fall in plasma oncotic pressure. Although venous hypertension is a well-recognized cause of pleural effusion, the frequency with which hypoalbuminemia in the absence of volume expansion leads to pleural effusion is unclear.

We determined the frequency with which unexplained pleural effusions occur in patients with normal and low plasma oncotic pressures.

A 2-month prospective screen of all admission patients to the University of Oklahoma Hospital and the Oklahoma City Veterans Administration (VA) Medical Center identified 152 patients who had chest radiographs and serum protein determinations on admission, but did not have an admission diagnosis that was a recognized cause of pleural effusion. In order to include more patients in the study with extremely low serum albumin levels, 20 additional study patients with serum albumin levels of < 2.0 g/dL were identified by a retrospective review of patients admitted during the previous 12 months. On the radiograph, pleural effusions were identified as a new blunting of the costophrenic angles. Study patients were divided into the following three groups: group 1 had serum albumin levels of > 3.5 g/dL; group 2 had serum albumin levels between 2.1 and 3.5 g/dL; and group 3 had serum albumin levels of < or = 2.0 g/dL. Finally, the frequencies with which pleural effusions occurred were compared among the three groups.

Seven of 104 patients in group 1, 2 of 45 patients in group 2, and 3 of 21 patients in group 3 had pleural effusions. Within each group, there were no significant differences in serum albumin concentration or plasma oncotic pressure between patients with and without pleural effusions. In all but two study patients, a careful review of records and a prospective follow-up of the patients' clinical course identified a potential cause for the effusions other than hypoalbuminemia. None of the 68 study patients with serum albumin levels of < or = 3.5 g/dL had an unexplained pleural effusion.

We conclude that hypoalbuminemia, per se, is an uncommon cause of pleural effusion. The recognition of pleural effusions in patients with low serum albumin levels should prompt careful clinical evaluations to identify other potential causes for the effusions.