From the Guidelines
The sensitivity of cytology for pleural fluid analysis is approximately 60% to 72%, with the most recent and highest quality study suggesting a mean sensitivity rate of about 72% when at least two pleural fluid specimens are submitted 1. This means that cytology will correctly identify malignant cells in pleural effusions in about 60% to 72% of cases where cancer is actually present. The sensitivity varies depending on several factors including the type of malignancy, with adenocarcinomas generally having higher detection rates than lymphomas or mesotheliomas. Some key points to consider when interpreting the sensitivity of cytology for pleural fluid analysis include:
- Multiple samples improve sensitivity, with the first sample yielding about 65% sensitivity, increasing to around 90% with two or more samples 1.
- For optimal results, at least 50 mL of pleural fluid should be sent for cytological examination, as submitting more than 50 mL of pleural fluid does not increase the diagnostic yield 1.
- The sample should be processed promptly to prevent cellular degradation, and fresh specimens yield better results than those with delayed processing.
- The specificity of pleural fluid cytology is quite high, typically exceeding 90%, meaning false positives are uncommon 1. In cases where cytology is negative but malignancy is still suspected, additional diagnostic procedures such as pleural biopsy, thoracoscopy, or image-guided biopsy may be necessary to establish a diagnosis. It's also worth noting that the diagnostic yield for malignancy depends on sample preparation, with a higher yield when both a cell block and a smear are prepared from the collected sample, and the experience of the cytologist 1. Overall, while cytology is a useful diagnostic tool for detecting malignancy in pleural fluid, it should be used in conjunction with other diagnostic procedures and clinical judgment to ensure accurate diagnosis and effective treatment.
From the Research
Sensitivity of Cytology for Pleural Fluid Analysis
The sensitivity of cytology for pleural fluid analysis varies depending on the type of tumor.
- The overall diagnostic sensitivity of pleural fluid cytology for malignant pleural effusions (MPE) was found to be 58.2% (95% CI 52.5% to 63.9%) 2.
- Sensitivity was highest in lung adenocarcinoma (83.6%; 95% CI 77.7% to 89.6%) and lowest in lung squamous cell carcinoma (24.2%; 95% CI 17.0% to 31.5%) and mesothelioma (28.9%; 95% CI 16.2% to 41.5%) 2.
- For malignancies with extrathoracic origin, sensitivity was high for ovarian cancer (85.2%; 95% CI 74.2% to 96.1%) and modest for breast cancer (65.3%; 95% CI 49.8% to 80.8%) 2.
- Another study found the sensitivity of pleural fluid cytology to be 75.0% (95% confidence interval (CI) 67.4-81.6%) 3.
- The sensitivity of pleural fluid cytology was also found to be 55.0% in patients with pulmonary metastases and malignant PE 4.
- A retrospective cohort study found that the sensitivity of thoracentesis with pleural fluid cytology varied from a low of 0.38 (95% CI 0.13-0.68) in head and neck malignancy to a high of 93 (95% CI 88-97) in breast cancer, and 100 (95% CI 0.82-100) in pancreatic cancer 5.
Factors Affecting Sensitivity
Several factors can affect the sensitivity of cytology for pleural fluid analysis, including:
- Tumor type: The sensitivity of cytology varies significantly depending on the type of tumor 2, 5.
- Pleural fluid characteristics: Cloudy appearance of pleural fluid and yellow/gold pleural fluid can reduce the odds of false negative pleural cytology 3.
- Pleural thickening: Pleural thickening on computed tomography scan can be a risk factor for false negative cytology 3.
- Amount of fluid drained: Larger amount of fluid drained can increase the risk of MPE 5.
- Pleural fluid protein: Higher pleural fluid protein can increase the risk of MPE 5.