How much is enough: investigation of pleural fluid cytology findings related to sample volume.

Introduction: Cytologic evaluation of pleural effusion samples plays an invaluable role in patient care. Despite this, only a few robust studies have investigated the optimal specimen volume for cytologic evaluation. It is not unusual for our laboratory to receive low-volume pleural effusion samples. Thus, as a part of ongoing quality assurance studies, we examined the performance of low-volume samples.

Materials And Methods: All pleural effusion samples received during a 1-year period from January 1, 2020 to December 31, 2020 were reviewed. The case data collected included the clinical indications, diagnostic categorization, cell block performance, and adequacy notations. Follow-up data were also collected. The cases were placed into low-volume (≤10 mL, 11-25 mL, and 26-50 mL) and higher volume (>50 mL) groups for analysis.

Results: A total of 226 samples were included in the present study. Of the 226 samples, 89 had a volume of ≤50 mL, including 32 with a very low volume of ≤10 mL. Significantly fewer positive cases were diagnosed in the ≤10-mL group relative to the >50-mL group (6.3% versus 27.7%) with significantly fewer cell blocks performed (15.6% versus 57.7%). However, only 7 of the ≤10 mL cases (21.9%) had been performed to rule out malignancy, significantly less than that for the >50 mL group (81 of 137; 59.1%). Additionally, none of the very-low-volume cases had an upgraded follow-up effusion sample.

Conclusions: The exact role of the sample volume is not entirely clear as there are many factors are at play beyond volume itself. Although larger specimen volumes might be more optimal for a number of reasons, malignancy can be diagnosed at even low sample volumes. Thus, there is value to examining all samples regardless of the volume received. Insertion of an adequacy comment might be prudent for low-volume cases, especially those with a high clinical concern for malignancy.