Interpretation of flow cytometric measurement of lymphocytes after fluorescein angiography.

Abstract

By use of flow cytometry (FCM), lymphocyte subsets were evaluated with fluorochrome-labeled monoclonal antibodies (MoAbs). Recent fluorescein angiography (FA) produces temporary elevation of serum background fluorescence at certain wavelengths of light, producing falsely decreased lymphocyte subset quantitations. The authors evaluated the duration of this effect on one subset of lymphocytes after FA. CD4 counts were determined by FCM before and 10 minutes, 1, 6, and 24 hours after injection of fluorescein dye in 12 patients. The MoAbs used were directly conjugated to fluorescein isothiocyanate (FITC) or phycoerythrin (PE). Using FITC-labeled MoAbs, falsely decreased CD4 counts occurred in all patients at 10 minutes and in all but one patient 1 hour after injection. Return to baseline levels occurred in 50% (95% confidence interval [CI], 0.21, 0.79) by 6 hours and in 75% (95% CI, 0.43, 0.95] by 24 hours. No such effect was observed using PE-labeled MoAbs. Falsely decreased CD4 values as determined by FCM were present immediately after FA in all 12 patients and persisted 24 hours in some patients when FITC-labeled MoAbs were used. CD4 evaluation should be delayed in patients who have undergone recent FA or the analysis should be performed with PE-labeled MoAbs.