Quantitative estimation of red-cell uptake in the spleen using⁸¹Rb – and⁵¹Cr-labelled red cells

Abstract

A method is described for converting the data obtained by external counting after administration of 51Cr-labelled red cells into a quantitative measurement of splenic sequestration. This involves the administration at a later stage of a second sample of red cells, which are double labelled with 81Rb and 51Cr and are damaged in vitro with l-mercuri-2-hydroxypropane to ensure their preferential uptake by the spleen. By means of a scan of the 81Rb activity the fractional uptake of the in vitro-damaged cells by the spleen can be measured, and then related to the external count. This permits the sequestration by the spleen of 51Cr-labelled natural cells to be estimated quantitatively. This provides a more reliable measurement than external counting alone in evaluating the role of the spleen in haemolytic anaemias and the indications for splenectomy. The reasons for selecting 81Rb and the theoretical considerations are presented. The method has been applied in a study on a patient suffering from hereditary spherocytosis. There was an uptake of 14·3 per cent of 51Cr-labelled red cells in the spleen in a 15-day period. This represented approximately 28 per cent of the 51Cr-labelled cells.