Examination of cytological smears and clot sections prepared from pleural fluids: a comparative study

Between January 1989 and May 1990, the Department of Cytology of Llandough Hospital examined 784 pleural fluid cytological preparations, 99 of which were also examined as paraffin wax sections of clots that had formed. To assess whether this practice yields worthwhile information, we reviewed the cytology and clot sections of 99 patients with pleural effusions and correlated the results with subsequent histology and review of clinical case notes. The specificities of each method separately and when combined was high: 92% clot section, 85% smear cytology and 85% combined. The sensitivity using clot section alone was 49%, smear cytology alone 46% and in combination, 54%. Analysis showed no significant difference between sensitivities. When pleural fluid clot formation occurs, we recommend the continued examination of clot sections, since it yields an increase in positive diagnoses, albeit not statistically significant.