Comparison of the clinical microscopy laboratory with the cytopathology laboratory in the detection of malignant cells in body fluids

The clinical microscopy (fluids) laboratory evaluates almost every body fluid that is obtained in the hospital. Because the fluids laboratory functions at all hours, it is often the first laboratory to receive a body fluid. In addition to its primary purpose of quantitating categories of cells, the medical technologist in this laboratory has an opportunity to identify malignant cells. To our knowledge, no formal study has ever been undertaken to evaluate the performance of the fluids laboratory in detecting malignancy. The authors therefore retrospectively identified 928 body fluids (pleural, peritoneal, cerebrospinal, and miscellaneous) over a 2-year period that had undergone simultaneous cytologic examination in our cytopathology laboratory and body fluid analysis in our fluids laboratory. Of these, a cytologic diagnosis of malignancy was made by the cytopathology laboratory in 107 cases; 821 were considered to be benign. No false-positive results were rendered by the fluids laboratory (100% specificity), but only 26 of the 107 malignant cases were identified (24% sensitivity); the overall accuracy was 93%. Factors contributing to the inability of the fluids laboratory to identify malignant cells included (1) too few cells to warrant a cytocentrifuge preparation, especially in cerebrospinal fluid specimens; (2) differences in the processing of specimens; (3) differences in staining procedures; and (4) differences in the training of personnel. The authors conclude that although the fluids laboratory correctly identifies neoplastic cells in approximately one fourth of the cases in which they are present, it should not be expected to detect malignant cells in every cytologically malignant case. Unless these contributing factors can be addressed and corrected, the fluids laboratory should never replace the cytopathology laboratory in the evaluation of body fluids for the presence of malignant cells.