Diagnostic pitfalls in effusion fluid cytology.

Effusion fluid cytology has propensity for both false positives (in up to 0.5%) and false negatives (in up to 30%) results. Methodical approach from collection step to final interpretation stage could prevent both false positives and false negatives, if the interpreter is familiar with various factors responsible for diagnostic pitfalls in effusion fluid cytology. For this discussion, these factors are categorized as mentioned below: Surface tension-related alterations in cytomorphologyImproper specimen processingMany faces of reactive mesothelial cells, overlapping with those of cancer cellsProliferation-related featuresDegenerative changes, such as nuclear hyperchromasia and cytoplasmic vacuolationUnexpected patterns and unusual entities.