A PITFALL IN CALCULATING DIFFERENTIAL RENAL-FUNCTION IN PATIENTS WITH RENAL-FAILURE

Measurement of relative renal function in azotemic patients can be misleading due to elevated background activity and delayed renal concentration of radiotracer. When there is delayed excretion of the tracer and obvious splenic or hepatic activity superimposed over one of the kidneys, it often is advantageous to delay the differential uptake measurement to allow renal activity to increase and background activity to decrease rather than use the standard 1- to 2- or 2- to 3-minute interval after radiopharmaceutical injection. The accompanying case illustrates the use of delayed images to obtain a more accurate assessment of relative renal function. The measurement must be made before the excretion of tracer into the ureter or bladder.