Flow cytometry of leukocytes after intravenous fluorescein angiography

Blood specimens were obtained for T lymphocyte analysis from patients undergoing intravenous fluorescein angiography (IVFA). Mononuclear cells were prepared by differential density centrifugation and analyzed by flow cytometry (FCM). Prior to IVFA, there was very little autofluorescence in the mononuclear cell population. After IVFA, there was an increase in the fluorescence of the mononuclear cells. Though barely visible by fluorescence microscopy, the fluorescence was uniformly distributed throughout the cytoplasm. By FCM, fluorescein was detected in 27% of the lymphocytes, 61% of the monocytes, and 75% of the granulocytes. Care must be taken when interpreting flow-cytometric lymphocyte subset data because of the increased nonspecific fluorescence of mononuclear cells in patients who have undergone IVFA.