Renin is an enzyme released by the juxtaglomerular apparatus of the kidney in response to decreased extracellular fluid volume, serum sodium, and renal perfusion pressure. It catalyzes the conversion of angiotensinogen, produced by the liver, to angiotensin I. Angiotensin I is then converted to angiotensin II in the lungs. Angiotensin II elevates systemic blood pressure by causing vasoconstriction and by stimulating the release of aldosterone.

Renin released by the kidneys is found initially in the renal veins. Thus, the output of renin by each kidney may be determined by obtaining samples directly from the right and left renal veins and comparing the results with those obtained from an inferior vena cava sample. This test is indicated when renal artery stenosis is suspected, because the kidney affected by decreased perfusion releases higher amounts of renin. Renal vein assay for renin is performed using fluoroscopy and involves cannulation of the femoral vein and injection of dye to aid in visualizing the renal veins. Because this is an invasive procedure, a signed consent is required.

Note: Values for peripheral vein samples should be substantially higher (e.g., 2.9-24 [ng/hr]/mL) in clients who are sodium depleted and in the upright position. These values also may vary according to the laboratory performing the test.

• Failure to follow dietary restrictions, if ordered, before the test may affect the test results.
• Failure to take prescribed diuretics, if ordered, before the test may affect the test results.
• Failure to maintain required positioning (e.g., upright versus recumbent) for at least 2 hours before the test may affect the test results.
• High-dose adrenocorticosteroid therapy, excessive salt intake, and excessive licorice ingestion may produce decreased levels.

• Assessment of renin production by the kidneys when client has hypertension of unknown etiology or when other disorders associated with altered renin levels are suspected:
  • Elevated renin levels are seen in renovascular and malignant hypertension, adrenal hypofunction (Addison's disease), salt-wasting disorders, end-stage renal disease, renin-producing renal tumors, and secondary hyperaldosteronism.
  • Decreased levels are associated with primary hyperaldosteronism, hypervolemia, excessive salt ingestion or retention, excessive adrenocorticosteroid levels resulting from either disease or drug therapy, and excessive licorice ingestion.
  • Renin levels may be high, low, or normal in essential hypertension.
  • In primary hyperaldosteronism, plasma renin levels are decreased, even with salt depletion before the test (results should be evaluated in relation to the serum aldosterone level, which is elevated in primary hyperaldosteronism).
  • Suspected renal artery stenosis as the cause of hypertension, as indicated by renal vein output of renin by the affected kidney more than 1.4 times that of the vena cava sample

Nursing Alert

• The renal vein assay for renin should be performed with extreme caution, if at all, in clients with allergies or previous exposure to radiographic dyes.

Nursing Care Before the Procedure

Client preparation varies according to the method for obtaining the sample and the factors to be controlled (e.g., salt depletion).

1. Peripheral vein, normal salt intake. Client preparation is essentially the same as that for any test involving collection of a peripheral blood sample. The client should follow a normal diet with adequate salt and potassium intake. Licorice intake and certain medications may be restricted for 2 weeks or more before the test, although this practice should be confirmed with the person ordering the study. The position relevant to the type of sample (e.g., upright versus recumbent) should be maintained for 2 hours before the test.
2. Peripheral vein, sodium depleted. Client preparation is the same as just described, except that a diuretic is administered for 3 days before the study and dietary sodium is limited to "no added salt" (approximately 3 g/day). Sample menus should be provided. The purpose of the diuretic therapy and sodium restriction should be explained, and client understanding and ability to follow pretest preparation should be ascertained.

Explain to the client:

• The purpose of the study
• That a "no added salt" diet must be followed for 3 days before the study
• That prescribed diuretics must be taken for 3 days before the study
• Other restrictions in diet (e.g., licorice) or drugs necessary before the study
• That the test will be performed in the radiology department by a physician and will take about 30 minutes
• The general procedure, including the sensations to expect (momentary discomfort as the local anesthetic is injected, sensation of warmth as the dye is injected)
• Whether premedications will be given
• After-procedure assessment routines (e.g., frequent vital signs) and activity restrictions

Encourage questions and verbalization of concerns appropriate to the client's age and mental status. Then:

• Question the client about possible allergies to radiographic dyes.
• Ensure that signed consent has been obtained.
• To the extent possible, ensure that the dietary and medication regimens and restrictions are followed.
• Assist the client in maintaining the upright position (standing or sitting) for 2 hours before the test, if ordered, to stimulate renin secretion.
• Take and record vital signs and have the client void; provide a hospital gown.
• Administer premedication, if ordered.
• Obtain a stretcher for client transport.

The procedure varies with the method for obtaining the sample.

1. Peripheral vein. A venipuncture is performed and the sample collected in a chilled lavender-topped tube. The tube should be inverted gently several times to promote adequate mixing with the anticoagulant, placed in ice, and sent to the laboratory immediately.
2. Renal vein. The client is assisted to the supine position on the fluoroscopy table, and a site is selected for femoral vein catheterization. The skin may be shaved (if necessary), cleansed with an antiseptic, draped with sterile covers, and injected with a local anesthetic.

A catheter is inserted into the femoral vein and advanced to the renal veins under fluoroscopic observation. Radiographic dye may be injected into the inferior vena cava at this point to aid in identification of the renal veins. A renal vein is entered and a blood sample obtained. The other renal vein is then entered and a second blood sample obtained. The catheter is then retracted into the inferior vena cava and a third sample obtained.

The samples are placed in chilled lavender-topped tubes that are labeled to identify collection sites. The tubes should be inverted gently several times to promote adequate mixing with the anticoagulant, placed in ice, and sent to the laboratory immediately.

The femoral catheter is removed after the third sample is obtained, and pressure is applied to the site for 10 minutes. A pressure dressing is then applied.

Nursing Care After the Procedure

1. Peripheral vein. Care and assessment after the procedure are the same as for any study involving the collection of a peripheral blood sample. Pretest diet and medications, which may have been modified or restricted before the study, should be resumed.
2. Renal vein. Maintain the client on bed rest for 8 hours after the procedure. Monitor vital signs and record according to the following schedule: every 15 minutes for 1 hour, every 30 minutes for 1 hour, and every hour for 4 hours. Monitor the catheterization site for bleeding or hematoma each time vital signs are checked. Resume previous diet and medications.
   • Abnormal values: Note and report results and correlate with urinary sodium, serum, and urinary aldosterone. Monitor blood pressure, especially if antihypertensive medications have been withheld. Monitor I&O for fluid deficit or excess.
   • Allergic response (renal vein): Note and report allergic response to dye injection and assess for rash, urticaria, dyspnea, and tachycardia. Administer ordered antihistamine or steroids and oxygen. Have emergency equipment and supplies on hand.
   • Vein thrombosis (renal vein): Note and report any flank or back pain, hematuria, or abnormal renal test results (blood urea nitrogen, creatinine).