How to check for renal artery stenosis?

Renal artery stenosis is a common renal vascular disease in clinical practice. The vast majority of renal artery stenosis is caused by atherosclerosis. This type of disease is more common among the elderly and young women. Many people like to diagnose diseases based on symptoms, which is particularly prone to misdiagnosis. No matter what the disease is, professional medical examinations should be conducted. So how should renal artery stenosis be examined?

1. Peripheral plasma renin activity measurement

It is one of the preferred screening tests for renovascular hypertension. A blood test in the morning sitting position is important for determining abnormally high renin secretion. It is elevated in 3/4 patients with renovascular hypertension. Peripheral renin levels can represent the level of renal vein renin secretion. Patients with significantly elevated PRA have better surgical outcomes. However, there is not a simple parallel relationship between PRA and blood pressure. Moreover, there are certain "false positives" and "false negatives" in PRA determination. Therefore, an increase in PRA only indicates the possibility of renal vascular hypertension, and further tests of renal vein renin activity and ACEI should be performed on both sides.

2. Captopril test

This is the most sensitive test for diagnosing renovascular hypertension, but it cannot distinguish whether the lesions are bilateral or unilateral. After the administration of captopril, the renin responsiveness of patients with renovascular hypertension increased far more than that of patients with essential hypertension. The criteria for judging a positive test result are: ① after stimulation, plasma renin activity >12 ng/(ml·h); ② the absolute value of plasma renin activity increases by 10 ng/(ml·h) or more; ③ the percentage of increase in plasma renin activity reaches 150% or more. If the basal level of plasma renin activity is lower than 3 ng/(m1·h), the percentage of increase should reach 400%. The test has a sensitivity and specificity of 95%, which is suitable for patients taking beta-blockers, but has poor reliability for patients with azotemia. For those with negative test results, the surgical effect is poor.

3. Renal B-ultrasound and color Doppler vascular ultrasound

The examination has high specificity and can demonstrate the renal artery anatomy, intrarenal hemodynamics, and kidney volume. In clinical practice, conventional ultrasound is generally combined with Doppler ultrasound to screen and follow up renal artery stenosis by measuring the hemodynamic indicators of the renal artery (i.e. resistance index, pulsatility index, difference between the resistance index or pulsatility index of both kidneys, systolic acceleration index, systolic acceleration time, etc.).

4. Radionuclide examination

There are two examination methods: radionuclide renogram and captopril renogram.

(1) Radionuclide renal examination: The radionuclides used for renal examination are 131I-sodium hippurate and Tc-diethylenetriamine (99m Tc-DTPA). 80% of the former is taken up by renal vascular epithelial cells and secreted into the renal tubular lumen, and 20% is filtered from the glomerulus and can be used to measure kidney size and renal blood flow. The latter is mainly filtered from the glomerulus and can be used to measure GFR. Radionuclide renography has high false-positive and false-negative rates (20% each) and is therefore generally not used as a screening test for renovascular hypertension.

(2) Captopril renal tracing: Oral administration of 25-50 mg of captopril was performed, and the renal tracings were compared 60 minutes before and after administration. If there is functionally significant stenosis, since captopril eliminates the contractile effect of AngII on the afferent arterioles, the GFR will be reduced by more than 10% compared with before taking the medicine, which is positive and can be used to judge whether there is functionally significant stenosis. Its diagnostic sensitivity and specificity were 80% and 95%, respectively. The criteria for diagnosing renal artery stenosis are: ① 1.5 to 2.5 minutes after injection of the radionuclide, the asymmetric uptake of the radionuclide by the kidney exceeds 60%; ② The peak is delayed; ③ 15 to 20 minutes after injection of the radionuclide, the peak activity percentage is higher than normal.

5. Magnetic resonance angiography (MRA)

It includes time-of-flight MRA, phase contrast MRA and three-dimensional gadolinium-enhanced MRA (3D-CE-MRA). Its resolution is sufficient to observe blood vessels as small as 1 mm in diameter within the renal parenchyma, and the diagnosis rate of renal artery lesions is 91.1%.

6. CT Angiography (CTA)

CTA can provide detailed information about the aorta and renal arteries. The sensitivity and specificity for diagnosing proximal renal artery atherosclerosis are both over 90%.