Holding ARBs Before Captopril Renogram
Angiotensin Receptor Blockers (ARBs) should be held for 2 to 5 days before performing a captopril renogram to prevent false-negative results. 1
Rationale for Medication Withdrawal
The American College of Cardiology guidelines explicitly state that ACE inhibitors are best withheld for 2 to 5 days before the test to reduce the possibility of a false negative result that may be seen with long-term ACE inhibition. 1 While these guidelines specifically mention ACE inhibitors, the same principle applies to ARBs since both drug classes block the renin-angiotensin-aldosterone system at different points but achieve similar functional effects on glomerular hemodynamics. 2
Mechanism Behind the Recommendation
Captopril renography works by acutely blocking angiotensin II-mediated efferent arteriolar vasoconstriction, which unmasks the hemodynamic significance of renal artery stenosis by causing a detectable decrease in glomerular filtration rate on the affected side. 1
Chronic blockade of the renin-angiotensin system (whether by ACE inhibitors or ARBs) may already be exerting this effect, potentially blunting the acute response to captopril administration and leading to false-negative results. 1
Research has shown that in patients on chronic ARB therapy, adding captopril can still produce diagnostic changes, but this was studied in the context of acute captopril addition to ongoing ARB therapy, not as a replacement for proper medication withdrawal. 3
Practical Implementation
The 2-5 day withdrawal period allows sufficient washout of the medication while maintaining a reasonable timeframe for clinical scheduling. 1
Other antihypertensive medications (except other renin-angiotensin system blockers) may generally be continued during this period. 1
Patients should be adequately hydrated before the test, particularly if they are taking diuretics. 1
Blood pressure should be monitored frequently during the procedure, especially after captopril administration. 1
Important Caveats
The guidelines note that beta-blockers, centrally acting drugs, and diuretics should ideally be stopped for approximately 2 weeks before testing when feasible, though this is more relevant for plasma renin activity testing than for captopril renography specifically. 2
Long-acting calcium channel blockers and alpha-receptor antagonists can be used as alternative antihypertensive agents during the withdrawal period as they minimally interfere with the test. 2
The test's sensitivity may be reduced in patients with bilateral renal artery stenosis, severe renal impairment, or urinary obstruction, regardless of medication withdrawal. 1, 4
In patients with glomerular filtration rate below 10 ml/min/1.73 m² or split renal function of 10% or less, scintigraphic parameters become nonspecific and the test may not be reliable. 4