Plasma Renin assay, Plasma Renin Activity, Angiotensin
Sample
- Venous blood of the patient is needed and use EDTA as the anticoagulant.
- EDTA preserve the angiotensin.
- Draw blood in the chilled tubes and while in the transportation keep the sample on ice.
- A fasting sample is needed.
- 24 hours of urine sodium is also helpful in making the diagnosis.
Precautions
- Stop 2 to 3 weeks before the use of diuretics, estrogen, and antihypertensive drugs (beta-blockers and ACE inhibitors).
- Stop taking foods containing caffeine like tea or coffee, one day before the test.
- Advise a low sodium diet 3 days before this test.
- There should be fast for at least 8 hours.
- Renin assay will be affected when the patient is taking:
- Aspirin.
- Taking high doses of corticosteroids.
- There will be a change in pregnancy.
- There will be an effect on the position of the patient.
Purpose of the test (Indications):
- This test is advised in a patient with hypertension.
- This test differentiates hypertension whether essential, renal, or renovascular.
- This test differentiates primary aldosteronism.
Pathophysiology
- Renin is enzymes released by the juxtaglomerular apparatus of the kidneys into the renal vein in response to:
- Hyperkalemia.
- Sodium depletion.
- Hypovolemia.
- Decreased kidney blood perfusion.
- Renin-angiotensin system:
- Renin is the enzyme of the hydrolase class which will catalyze the cleavage of angiotensinogen to create angiotensin I.
- Angiotensinogen is derived from the liver and is alpha-2 globulin.
- Angiotensin I is converted to angiotensin II in the lung where there is an abundance of the angiotensin-converting enzyme.
- Angiotensin II is the potent vasopressor agent responsible for the renal type of hypertension.
- Angiotensin II also releases aldosterone from the adrenal cortex.
- Angiotensin II + aldosterone both leads to :
- Hypertension.
- Increase in the blood volume.
- Serum sodium.
- The Renin+aldosterone regulate:
- Sodium and potassium balance.
- Blood pressure.
- Blood volume.
- Renin is released when there is:
- Low plasma volume.
- Low blood pressure.
- Low sodium.
- Increased Potassium.
- Renin release is suppressed when there is:
- Loss of potassium.
- Increased blood volume.
- An acute increase in blood pressure.
- Renin value increases when the position changes from the recumbent to upright.
- High sodium intake decreases the renin level.
- The measurement of plasma renin activity is used in the differential diagnosis of hypertension.
- Renin stimulation test is advised to diagnose and differentiate between primary and secondary hyperaldosteronism.
Normal
Source 1
Normal Plasma Angiotensin I level
Angiotensin1
Age | ng /mL/hour |
Cord blood | 4.0 to 32.0 |
Newborn 1 to 7 days | 2.0 to 35.0 |
Child Normal sodium diet, supine | |
1 to 12 month | 24.0 to 37.0 |
1 to 3 years | 1.7 to 11.2 |
3 to 5 years | 1.0 to 6.5 |
5 to 10 years | 0.5 to 5.9 |
10 to 15 years | 0.5 to 3.3 |
Adult Normal, sodium diet | |
Supine | 0.2 to 1.6 |
Standing (4 hours) | 0.7 to 3.3 |
- To convert into SI unit x 1.0 = µg x hour -1 x L-1
Renin direct
- Adult =
- Supine = 12 to 79 mU/L
- Upright = 13 to 114 mU/L
Source 2
Plasma Renin assay
- Adult / elder:
- Upright position + sodium depletion (sodium-restricted diet)
- 20 to 39 years = 2.9 to 24 ng/mL/hour.
- >40 years = 2.9 to 10.8 ng/mL/ hours.
- Upright position + normal sodium intake
- 20 to 39 years = 0.1 to 4.3 ng/mL/hour.
- >40 years = 0.1 to 3 ng/mL/hour.
- Childre:
- o to 3 years= <16.6 ng/ mL/ hour.
- 3 to 6 years = <6.7 ng/ mL/ hour.
- 6 to 9 years = <4.4 ng / mL / hour.
- 9 to 12 years = <5.9 ng /mL / hour.
- 12 to 15 years = <4.2 ng / mL / hour.
- 15 to 18 years = <4.3 ng / mL / hour.
- Upright position + sodium depletion (sodium-restricted diet)
Source 5
Plasma renin assay
Normal sodium diet
- Adult
- supine = 0.2 to 1.6 ng/mL
- Standing = 0.7 to 3.3 ng/mL
Low sodium diet
- Adult
- Supine = Level increases 2 times the normal
- Standing = Level increases 6 times the normal
Another source
- Adults, on a normal sodium diet.
Patient age | Normal Angiotensin 1 ng/mL /hour |
Supine (adult) | 0.2 to 1.6 |
Standing for 4 hours (adult) | 0.7 to 3.3 |
Neonates cord blood | 4 to 2 |
Neonates 1 to 7 days | 2 to 35 |
Infants 1 to 12 months | 2.4 to 37 |
Children 1 to 3 years | 1.7 to 11.2 |
Children 3 to 5 years | 1 to 6.5 |
Children 5 to 10 years | 0.5 to 5.9 |
Children 10 to 15 years | 0.5 to 3.3 |
- (Note. These are from two different sources. Values vary depending on diet, health, age, and sex).
Increased Renin level is seen in:
- Secondary aldosteronism with malignant hypertension.
- Chronic renal failure.
- Renovascular hypertension.
- Salt losing status due to GI diseases.
- Renin producing tumor of the kidney.
- Pheochromocytoma.
- Few patients with essential hypertension around 15%.
- Reduced plasma volume due to low sodium.
- Drugs like diuretics.
- Addison disease.
- Cirrhosis.
- Hyperkalemia.
- Hemorrhage.
Decreased Renin level is seen in:
- Unilateral renal artery stenosis.
- Primary aldosteronism (98%).
- Congenital adrenal hyperplasia with 17- hydroxy deficiency.
- Administration of salt-retaining steroids.