Renin | Laboratory research

Renin is an enzyme belonging to the aspartyl-protease family; Renin synthesis was initially detected in the juxtaglomer apparatus of the kidney, but it was later found that it can also occur in the smooth muscle cells of the brain, heart, and arteries.

Renin circulates in two different forms: Prorenin და Active renin. Prorenin is a precursor of renin without enzymatic action; It is converted to active renin in the secretory granules of cells of the juxtaglomerular apparatus.

Active renin has substrate specificity and converts angiotensinogen to biologically inactive angiotensin I.

In turn, angiotensin I is broken down by angiotensin-converting action to form the active octapeptide angiotensin II, the most potent vasopressor, which plays an important role in regulating blood pressure. Angiotensin II also stimulates the production of aldosterone by the adrenal glands;

The renin-aldosterone system controls sodium and potassium balance, blood volume, and blood pressure. Sodium reabsorption in the kidneys affects plasma volume. Hypovolemia, hypotension, and hyponatremia stimulate renin secretion, leading to increased aldosterone levels. Aldosterone causes water retention, increased blood pressure, and loss of potassium.

Renin determination is useful in the differential diagnostics of hypertensive patients. Elevated plasma renin levels are observed in patients with hypertension caused by renal artery stenosis (renal vascular hypertension).

Renin testing may also be helpful in diagnosing patients with primary hyperaldosteronism who typically have low renin levels.

In addition, testing is recommended for patients with primary hyperaldosteronism, first-degree relatives with hypertension. For screening purposes, the guideline recommends estimating the aldosterone / renin ratio in these patients.

Plasma renin is also used to monitor cortisone replacement therapy in patients with adrenal insufficiency.

In most patients with essential hypertension, renin has normal or low levels. However, there is a group of patients in whom renin levels are elevated, which poses an increased risk of developing myocardial infarction or stroke.

When to take a test on renin?

• Differential diagnostics of primary and secondary hyperaldosteronism, with simultaneous determination of serum aldosterone levels by calculating the aldosterone / renin ratio and performing some functional tests;
• Diagnosis and management of patients with hypertension due to renal artery stenosis;
• Monitoring of cortisone replacement therapy in patients with adrenal insufficiency;
• Assessing the risk of vascular complications in patients with essential hypertension;

How to prepare for the test?

In order to detect primary hyperaldosteronism, it is recommended:

Treatment with the drugs that affect the test should be stopped at least 4 weeks before the test: potassium-sparing drugs (spironolactone, amiloride, triamterene, elferonone), potassium-sparing diuretics, and licorice root products (licorice).

1. Normal intake of table salt in patients (approximately 3 g of sodium per day) is recommended.
2. If it is necessary to maintain control of blood pressure, it is advisable to take drugs with reduced impact on the test.
3. It is mandatory to specify the patient's posture when taking the sample. In the supine position it is advisable to do the test early in the morning. During orthostatic posture it is essential that the patient remain in this position for at least 30 minutes before receiving the sample.
4. It is advisable to know in advance the concentration of sodium and potassium in the blood and urine.
5. You should avoid taking radioactive isotopes for 24 hours before.

Possible interpretation of the results

A primary hyperaldosteronism test is considered positive if the aldosterone / renin ratio is> 20. Then confirmatory tests (sodium load test, saline infusion test, fludrocortisone suppression test, or captopril test) are used.

Elevated plasma renin and serum aldosterone levels have been reported in renal artery stenosis.

Renin data are important for the appropriateness of performing visual studies of renal blood vessels.