[Iron and iron-binding proteins in the differential diagnosis of pleural effusion]

Iron, iron-binding capacity, lactoferrin and total protein were determined in the plasma and pleural fluid of 30 patients with cardiac failure (n = 10), infectious/inflammatory disease (n = 9) and metastatic carcinoma (n = 11). In 16 patients pleural transferrin and ferritin was also measured. Plasma iron and total iron-binding capacity were reduced in inflammatory and neoplastic disease, whereas hyposideremia with normal iron-binding capacity was seen in patients with heart failure. Plasma lactoferrin was reduced in metastatic carcinoma. Exudates (protein greater than or equal to 30 g/l; infectious/inflammatory: 9/9, carcinomatous: 10/11) had significantly higher iron, lactoferrin, transferrin and ferritin concentrations than transudates (protein less than 30 g/l; heart failure: 10/10, carcinomatous: 1/11). Statistically, infectious/inflammatory exudates could be distinguished from neoplastic exudates by a higher median iron concentration (non-parametric Wilcoxon-Mann-Whitney test). Overlap of the respective ranges, however, did not allow a clear-cut differential diagnosis in individual cases. Pleural lactoferrin concentrations, on the other hand, correlated with the pleural granulocyte count and nonspecifically reflect the degree of granulocytic inflammation. Positive pleural/plasma correlations of protein and of iron concentrations were found in exudates only. Within exudates and transudates, on the other hand, total protein correlated with transferrin but not with iron concentrations. Therefore, and because of the substantially higher pleural/plasma ratio for iron than for transferrin concentrations, a quantitatively important, non-transferrin bound iron pool in pleural fluids, most probably ferritin, must be assumed.(ABSTRACT TRUNCATED AT 250 WORDS)