Original Articles Utility of Hyaluronic Acid in Pleural Fluid for Differential Diagnosis of Pleural Effusions: Likelihood Ratios for Malignant Mesothelioma

The level of hyaluronic acid (HA) was determined in the pleural fluid of 99 patients, including 19 with malignant mesothelioma, 27 with lung cancer, 1 with breast cancer, 1 with mediastinal tumor and 51 with non-malignant diseases. With a cut-off level at 100 µg/ml, the pleural fluid concentration of HA was high in 36.8 % of patients (7 of 19) with malignant mesothelioma and 1.3 % of patients (1 of 80) with lung cancer and other malignant and non-malignant diseases. The mean concentration of pleural fluid HA was significantly higher in patients with mesothelioma than in those with lung cancer and other malignant and non-malignant diseases. The pre-test probability of MM was 5.9 % in this series. The LRs for ≥100, 50–99 and ≤49 µg/ml are 28.3, 3.3 and 0.5, respectively; these put the post-test probabilities at 64, 17 and 3%, respectively. Indeed, in cases of uncommon disease such as MM, the post-test probability is low even if the cut-off level of HA is ≥100 µg/ml. The discrimination between malignant mesothelioma and lung cancer needs special attention. In these two diseases, the LRs of MM for pleural fluid CEA>30, 10–30 and <10 ng/ml were 0.2, 1.9 and 2.4, respectively. The pre-test probability of MM for HA ≥100 µg/ml is 64%. Furthermore, because the LR for CEA is <10 ng/ml, the post-test probability is 81%. When the combination of two markers is considered, the high level of HA and the low level of CEA may be useful for the differential diagnosis of MM from pleuritis carcinomatosa. Key words: hyaluronic acid – carcinoembryonic antigen – CEA – lung cancer – pre-test probability – post-test probabilit