An improved method for radio-labelling leucocytes in vitro with Tc-99m d,1-HMPAO (Technetium-99m-d,1-hexamethyl propyleneamine oxime) for use in scintigraphic imaging of inflammatory lesions enhances the labelling efficiency by incubating the leucocytes with Tc-99m d,1-HMPAO in the presence of an acid citrate dextrose solution and by depleting residual RBCs from the leucocytes prior to such incubation step. The RBC depletion is accomplished by means of a rocking step.

An assay method for detecting the response or activation of cells, including lymphocytes, and a method for detecting immunological sensitization in a subject, which involves the introduction of cell-activating substance which causes an enzyme of the cells to become available for reaction, and the measurement of the enzymatic reaction using a substrate which generates a detectable product, and a kit for performing such assays.

Disclosed is a method for separating leukocytes from platelets. Blood serum is added to a centrifuge tube. A suspension containing leukocytes and platelets is then added to form a layer on top of the blood serum, the layer having a density less than the density of the blood serum. The cells and the layers are centrifuged at a force and for a time sufficient to separate the leukocytes from the platelets. The resulting, isolated leukocytes are then recovered from the centrifuge tube. In some embodiments, a suspension of the leukocyte cells are pretreated by incubating with a stannous ion reducing agent, the suspension having a stannous ion concentration of from about 50 .mu.g to about 1000 .mu.g stannous ion per 10.sup.8 leukocyte cells. A suspension of the pretreated leukocyte cells is then incubated with a solution containing a technetium-99m (VII) salt, preferably sodium .sup.99m Tc-pertechnetate, to radiolabel the leukocyte cells.