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Cytology is more sensitive than blind biopsy in patients suspected of serosal metastases, presumably because fluid provides a more representative sample. Cytologic examination supplemented by culture of the fluid is more reliable than a biopsy to detect tuberculosis.
Cytologic examination of the effusions has a substantial false-negative rate. Some studies estimated the sensitivity of cytology for the diagnosis of malignancies at about 60%. The detection rate increases when multiple specimens are used.
False-positive diagnoses occur in less than 1% of benign cases. They are usually caused by mesothelial cell atypia in the setting of pulmonary infarction, tuberculosis, chemotherapy, acute pancreatitis, ovarian fibroma, cirrhosis. False positive results may also occur due to misinterpretation of benign lymphoid cells as a lymphoma.
Adjunctive techniques to improve sensitivity, particularly immunocytochemistry, are useful in selected cases.
Immunocytochemistry can be very helpful in the following cases:
- Confirming malignancy in cytologically equivocal cases
- Distinguishing adenocarcinoma from mesothelioma
- Establishing the primary site of a malignant effusion