What is the role of a renogram in the workup of renovascular hypertension (RVHT)?

Updated: Dec 01, 2020
  • Author: Rebecca J Schmidt, DO, FACP, FASN; Chief Editor: Vecihi Batuman, MD, FASN  more...
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Answer

Because of its high false-negative rate (20-25%), the nonstimulated renal scan has limited efficacy and is not universally recommended as a screening test. The predictive value of radioisotope scanning, however, can be enhanced by the administration of captopril orally (25-50 mg) 1 hour before the isotope is injected. Decreased function after treatment with captopril indicates a high likelihood of renovascular stenosis. If the scan findings remain normal, renovascular disease is not ruled out.

A marker of glomerular filtration (eg, diethylenetriamine pentaacetic acid [DTPA]) or compounds that are secreted by the proximal tubule (eg, hippurate, mercaptotriglycylglycine [MAG-3]) can be used to estimate total, as well as differential, kidney function—information that may be useful in the assessment of treatment options. The latter may be more reliable in patients with renal insufficiency.Removal of angiotensin II–mediated vasoconstriction by ACE inhibition induces a decline in the GFR of the stenotic kidney and often an equivalent increase in the GFR of the contralateral kidney. The difference in the GFR between the 2 kidneys is enhanced by radioisotope and is visible on the renogram.

Positive results from an ACE inhibitor renogram are determined according to the following 2 criteria:

  • Relative uptake of the isotope decreased, with 1 kidney accounting for less than 40% of the total GFR

  • Peak uptake of the isotope delayed to more than 10-11 minutes (normal, 3-6 minutes)

A slower washout of the isotope may occur in the stenotic kidney, as demonstrated in unilateral RAS by a delay of 5 minutes or longer in washout on the involved side. This criterion may be evaluated best with a compound such as hippurate, which is secreted into the tubules rather than only being filtered.

While the availability of more sophisticated imaging along with a number of limitations have relegated the renogram away from favor as a screening test for RVHT, it remains useful for determining differential (relative) function of each kidney in settings where a nephrectomy is contemplated.

 


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