Synonym/Acronym
Plasma renin activity (PRA), angiotensinogenase.
Rationale
To assist in evaluating for a possible cause of hypertension.
Patient Preparation
There are no fluid restrictions unless by medical direction. The patient should be on a normal sodium diet (1–2 g sodium per day) for 2 to 4 wk before the test. Inform the patient or family member that the position required (supine or upright) must be maintained for 2 hr before specimen collection. By medical direction, the patient should avoid diuretics, antihypertensive drugs, herbals, cyclic progestogens, and estrogens for 2 to 4 wk before the test. Protocols may vary among facilities.
Normal Findings
Method: Enzyme-linked immunoassay.
| Age and Position | Conventional Units | SI Units (Conventional Units × 1) |
|---|
| Newborn–12 mo | 2–35 ng/mL/hr | 2–35 mcg/L/hr | | Supine, normal sodium diet | | | | 1–3 yr | 1.7–11.2 ng/mL/hr | 1.7–11.2 mcg/L/hr | | 4–5 yr | 1–6.5 ng/mL/hr | 1.0–6.5 mcg/L/hr | | 6–10 yr | 0.5–5.9 ng/mL/hr | 0.5–5.9 mcg/L/hr | | 11–15 yr | 0.5–3.3 ng/mL/hr | 0.5–3.3 mcg/L/hr | | Adult | 0.2–1.6 ng/mL/hr | 0.2–1.6 mcg/L/hr | | Upright, normal sodium diet | | | | Children (4–15 yr) | Equal to or less than 15–17 ng/mL/hr | Equal to or less than 15–17 mcg/L/hr | | Adult–older adult | 0.5–4 ng/mL/hr | 0.5–4 mcg/L/hr |
Values vary according to the laboratory performing the test, as well as the patient’s age, gender, dietary pattern, state of hydration, posture, and physical activity. |
Study type: Blood collected in a lavender-top [EDTA] or pink-top [K2-EDTA] tube; related body system: Endocrine and Urinary systems. Specify patient position [upright or supine] and exact source of specimen [peripheral vs. arterial]. Venipuncture should be performed after the patient has been in the upright [sitting or standing] position for 2 hr. If a supine specimen is requested on an inpatient, the specimen should be collected early in the morning before the patient rises. The specimen should be immediately transported in an ice slurry to the laboratory.
Renin is an enzymatic peptide hormone secreted by the granular cells of the juxtaglomerular apparatus in the kidney in response to sodium depletion and hypovolemia. Renin activates the renin-angiotensin system through the conversion of angiotensinogen to angiotensin I. Angiotensin I is converted to the biologically active angiotensin II by angiotensin-converting enzyme primarily within the capillaries of the lungs. Angiotensin II is a powerful vasoconstrictor that ultimately maintains the appropriate perfusion pressure in the kidneys. Angiotensin II stimulates aldosterone production in the adrenal cortex, secretion of antidiuretic hormone from the pituitary, and stimulates the thirst reflex from the hypothalmus. The net effect is regulation of blood pressure by regulating arterial vasoconstriction and the movement of extracellular fluids such as plasma, lymphatic fluid, and interstitial fluid. Excessive amounts of angiotensin II cause renal hypertension. The random collection of specimens without prior dietary preparations does not provide clinically significant information. Values should also be evaluated along with simultaneously collected aldosterone levels (see studies titled “Aldosterone” and “Angiotensin-Converting Enzyme”).
Factors That May Alter the Results of the Study
- Drugs and other substances that may increase renin levels include albuterol, amiloride, azosemide, benazepril, bendroflumethiazide, captopril, chlorthalidone, cilazapril, desmopressin, diazoxide, dihydralazine, doxazosin, enalapril, felodipine, fenoldopam, fosinopril, furosemide, hydralazine, hydrochlorothiazide, laxatives, lisinopril, lithium, methyclothiazide, metolazone, muzolimine, nicardipine, nifedipine, opiates, oral contraceptives, perindopril, ramipril, spironolactone, triamterene, and xipamide.
- Drugs and other substances that may decrease renin levels include acetylsalicylic acid, angiotensin, angiotensin II, atenolol, captopril, carbenoxolone, carvedilol, clonidine, cyclosporin A, furosimide, glycyrrhiza, indomethacin, labetolol, levodopa, metoprolol, naproxen, nicardipine, NSAIDs (ibuprofen, sulindac), oral contraceptives, oxprenolol, potassium, propranolol, reserpine, and vasopressin.
- Upright body posture, stress, and strenuous exercise can increase renin levels.
- Diet can significantly affect results (e.g., low-sodium diets stimulate the release of renin).
- Hyperkalemia, acute increase in blood pressure, and increased blood volume may suppress renin secretion.
Before the Study: Planning and Implementation
Teaching the Patient What to Expect
- Discuss how this test can assist in evaluating for high blood pressure.
- Explain that a blood sample is needed for the test. Inform the patient that multiple specimens may be required.
Potential Nursing Actions
- Verify adherence to ordered pretest instructions regarding diet and medications.
After the Study: Implementation & Evaluation Potential Nursing Actions
Treatment Considerations
- Resume the usual medications, as directed by the health-care provider (HCP).
- Explain the importance of notifying the HCP of any signs and symptoms of dehydration or fluid overload related to abnormal renin levels or compromised sodium regulatory mechanisms.
- Fluid loss or dehydration is signaled by the thirst response. Decreased skin turgor, dry mouth, and multiple longitudinal furrows in the tongue are symptoms of dehydration.
- Fluid overload may be signaled by a loss of appetite, nausea, and pitting edema.
- Provide education on the importance of proper water balance. In the case of hard water, untreated tap water contains minerals such as calcium, magnesium, and iron. Water-softening systems replace these minerals with sodium, and therefore patients on a low-sodium diet should avoid drinking treated tap water and drink bottled water instead.
Nutritional Considerations
- Advise those with depleted sodium that the major source of dietary sodium is found in table salt, milk and other dairy products, and processed foods.
- Advise those on low-sodium diets to avoid beverages such as colas, ginger ale, sports drinks, lemon-lime sodas, and root beer. Many over-the-counter medications, including antacids, laxatives, analgesics, sedatives, and antitussives, contain significant amounts of sodium. A registered dietitian should be consulted before using salt substitutes.
- Explain that potassium is present in all plant and animal cells, making dietary replacement fairly simple to achieve.
Clinical Judgement
- Consider how to gain buy-in regarding reading food labels to help maintain a healthy sodium level.
Follow-Up and Desired Outcomes
- Recognizes the value of reading all food, beverage, and medicine labels to evaluate nutritional value.
- Understands that renin levels affect the regulation of fluid balance and electrolytes.