Diagnosing malignant pleural effusions: how do we compare?

Introduction Accurate and prompt diagnosis of malignant pleural effusion (MPE) is important as patients with suspected MPE often wait for many days before the diagnosis is secure. Aims (1) To evaluate the diagnostic yield of pleural fluid cytology for patients admitted to Middlemore Hospital (MMH) in Auckland, New Zealand with MPE between 31 May 2010-1 June 2011. (2) To document the waiting time for cytology results to be made available and whether this contributed to length of stay. (3) To evaluate whether the volume of pleural fluid analysed contributed to diagnostic yield. Methods A retrospective audit of pleural fluid cytology results on 36 consecutive patients admitted to MMH with a pleural effusion which was subsequently proven to be due to malignancy. Data was obtained from hospital medical records and Web Eclair databases. Results 54.8% (17/31) of patients had positive pleural fluid cytology. Initial pleural fluid cytology was positive in 16 (51.6%). Only 4/15 patients with negative pleural fluid cytology had a repeat aspiration (1 was positive). Median cytology turnaround time was 6.72 days, range 2.23-43.06 days. Average length of stay (ALOS) was 7.78 days, range 1.11-20.8 days. Cytology turnaround times seem shorter for inpatients and when a diagnosis of cancer is unknown but the ALOS is longer if patients have negative initial cytology and when a diagnosis of cancer is uncertain. Samples > 50mL appear to have a higher diagnostic yield compared to samples <= 50mL but this was not statistically significant (77.8% to 41.2%, p=0.08). Conclusion Diagnostic yield from pleural fluid cytology at our hospital is comparable with other documented studies. ALOS appears to be influenced by a negative initial pleural fluid cytology and the uncertainty of diagnosis of cancer, not cytology turnaround time. The results suggest a more efficient diagnostic and treatment algorithm could be considered with emphasis on Day Stay investigation and treatment.