From the Guidelines
The laboratory finding that best predicts whether an operation that relieves the obstruction will reduce the blood pressure to normal is increased renin activity in the affected kidney, as evidenced by a significant difference in renal vein renin levels between the affected and unaffected kidney. This is based on the understanding that in patients with unilateral renal artery stenosis (RAS), the ischemic kidney secretes increased renin, leading to asymmetry in renal vein renin levels 1. The use of renal vein renin assays to predict response to revascularization has been studied extensively, with earlier studies supporting its validity, but later studies revealing high rates of false-negative and false-positive results 1. However, the principle that increased renin activity in the affected kidney is a marker of renovascular hypertension remains a cornerstone in the diagnosis and management of this condition. Key points to consider include:
- The affected kidney increases renin production as a compensatory mechanism for reduced blood flow due to stenosis.
- A significant difference in renin levels between kidneys suggests that the stenotic kidney is the primary driver of hypertension.
- Other supportive findings may include elevated peripheral plasma renin activity, especially in response to ACE inhibitors, although the specificity and sensitivity of these tests can be limited 1. Given the complexities and limitations of diagnostic tests in this context, increased renin activity in the affected kidney remains the most relevant laboratory finding for predicting the success of revascularization in normalizing blood pressure.
From the Research
Laboratory Findings for Renal Artery Stenosis
The laboratory finding that best predicts whether an operation that relieves the obstruction will reduce the blood pressure to normal in a patient with hypertension due to renal artery stenosis is:
Rationale
Increased renin activity is a key indicator of renovascular hypertension, which is caused by the activation of the renin-angiotensin system in response to decreased blood flow to the kidney 4, 5, 3.
Predictive Value
Studies have shown that patients with renal artery stenosis who have increased renin activity are more likely to have their blood pressure normalized after relief of the obstruction 2.
Mechanism
The mechanism of renin release in renovascular hypertension is thought to be related to the decrease in hydrostatic pressure in the afferent arteriole, which stimulates the juxtaglomerular cells to release renin 3.
Clinical Implications
The presence of increased renin activity in a patient with renal artery stenosis suggests that the stenosis is causing renovascular hypertension, and that relief of the obstruction may lead to normalization of blood pressure 4, 5.