Evaluation of ⁵¹Cr as a Leucocyte Label

Summary. A double label technique has been developed to compare the behaviour of ⁵¹Cr labelled leucocytes with DF³²P labelled leucocytes. Whole blood is divided into two aliquots and the leucocytes in each are labelled with a different isotope. After infusion of labelled cells, the radioactivity of each isotope can be determined simultaneously on the same blood sample using liquid scintillation counting. In studies of seven patients with solid tumours and one with leukaemia, the intravascular disappearance of autologous leucocytes labelled with ⁵¹Cr and DF³²P appeared similar in five of the eight patients during the initial 6 hr following infusion. Thereafter in all but one instance, ⁵¹Cr labelled leucocytes had slightly higher specific activities. ⁵¹Cr labelled lymphocytes and DF³²P labelled lymphocytes also behaved in the same manner. It is concluded that⁵¹Cr is a suitable leucocyte label and may be substituted for DF³²P under certain circumstances.