Detection of acute infection/inflammation with Tc-99m labeled intact polyvalent human IgG

Intact polyvalent human immune globulin (IgG) labeled with Tc-99m by a mild chemical method was investigated with animals infected with either S. aureus or E. coli in the thigh muscle. Focal infection was clearly visualized by Tc-99m IgG scintigraphy within 1 h postinjection. Tc-99m IgG appeared to be concentrated in the liver, spleen, kidneys and urinary bladder. It cleared rapidly via the kidneys resulting minimal of tissue background activity and high infection-to-normal organ ratios. At 24 h postinjection, the ratios of infectious lesion to blood, normal muscle and bone averaged 10:1, 23:1, and 24:1 for S. aureus infection vs 4:1, 9:1 and 9:1 for E. coli infection, respectively. Tc-99m labeled IgG also concentrated in terpentine-induced aseptic inflammatory lesion with a target-to-blood ratio of 4:1, bone 6:1 and normal muscle about 10:1. These findings suggest potential value of Tc-99m IgG as an imaging agent for the early detection of focal infection and inflammation.