Mag3 Renal Scan Interpretation

Normal renogram curve

The shape of the renogram curve (following subtraction of background activity) is dependent on—

1. MAG3 uptake from blood into kidney

2. MAG3 elimination from kidney into bladder

Classically, the normal MAG3 renogram curve has three phases (see figure 4.1):

• The first phase: steep upward rise following intravenous contrast injection; this is indicative of the speed of tracer injection and its delivery to the kidneys (i.e., renal vascular supply)

• The second phase: a more gradual slope which represents renal handling of MAG3 (renal uptake by tubular secretion and glo-merular filtration) and peaks between 2 and 5 minutes. Time taken for the curve to peak following tracer injection is referred to as Tmax. This may be delayed in patients with renovascular insufficiency, renal failure, and obstruction

• The third phase: commences after the peak. Associated with the emergence of tracer in the bladder. Represents elimination (but also delivery) of tracer from the kidney. After 3 minutes

Mag3 Obstruction
FIGURE 4.1. MAG3—Renography curve patterns in F + 20 diuresis renography (with permission from Comprehensive Urology, Weiss, Mosby, 2001, 141)

both elimination and uptake are in competition, but the former subsequently dominates. It is this elimination curve that is dependent on the upper tract urodynamics. The elimination curve may have a smooth or stepwise (variant of normal) pattern and when normal, excludes the presence of obstruction. A delayed upward deflection may indicate intermittent obstruction or vesico-ureteric reflux

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