Identification of factors affecting technetium 99m leucocyte labelling by phagocytic engulfment and development of an optimal technique.

Human autologous leucocytes can be simply and reproducibly labelled by phagocytic engulfment of technetium 99m stannous colloid with high leucocyte-labelling efficiency (LLE), similar human biodistribution to indium-111-oxine labelled leucocytes and good cell viability. A mean particle size of 2.1 microns is optimal for phagocytosis and the most important parameter in maintaining reproducibly high neutrophil uptake. It is more critical than hitherto appreciated. When such variables as type of colloid, purity of starting materials, speed of mixer rotation when preparing colloid and labelling leucocytes, heparin concentration, freshness of colloid preparation, type of sterilising membrane filter used and incubation time of cells with colloid are rigidly controlled, consistent labelling efficiencies in excess of 90% can be obtained with neutrophil predominance. The lyophilised kit tested produced suboptimal results.