High RBC labeling efficiency by controlling pretinning with the modified in vivo/in vitro labeling method.

OBJECTIVE The image quality for gastrointestinal bleeding studies depends on the efficiency of red blood cell labeling. The in vitro technique has been used widely because of its high labeling efficiency. New data for the modified in vivo/in vitro method are lacking. This study reports on the high labeling efficiency that can be obtained with the modified in vivo/in vitro method and the pitfalls to avoid. METHODS A consecutive series of 91 labeling studies was analyzed. Different amounts of tin, red blood cell concentrations, and infusions of interfering substances also were studied. RESULTS A mean efficiency of red blood cell labeling of 97% (80%-99%) was obtained. Only 3 cases showed unacceptable results. Suboptimal results were obtained with amounts of tin below 10 microg SnCl2/kg body weight, a reduced hematocrit, and blood transfusion or infusion of HES solution during pretinning. CONCLUSION The modified in vivo/in vitro red blood cell labeling technique is performed easily, is useful and is comparable to the gold standard in vitro method, provided that the pretinning period is controlled carefully.