Plasma Renin assay, Plasma Renin Activity, Angiotensin

Sample

1. Venous blood of the patient is needed and use EDTA as the anticoagulant.
2. EDTA preserve the angiotensin.
3. Draw blood in the chilled tubes and while in the transportation keep the sample on ice.
4. A fasting sample is needed.
5. 24 hours of urine sodium is also helpful in making the diagnosis.

Precautions

1. Stop 2 to 3 weeks before the use of diuretics, estrogen, and antihypertensive drugs (beta-blockers and ACE inhibitors).
2. Stop taking foods containing caffeine like tea or coffee, one day before the test.
3. Advise a low sodium diet 3 days before this test.
4. There should be fast for at least 8 hours.
5. Renin assay will be affected when the patient is taking:
   1. Aspirin.
   2. Taking high doses of corticosteroids.
6. There will be a change in pregnancy.
7. 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

1. Renin is enzymes released by the juxtaglomerular apparatus of the kidneys into the renal vein in response to:
   1. Hyperkalemia.
   2. Sodium depletion.
   3. Hypovolemia.
   4. Decreased kidney blood perfusion.
2. Renin-angiotensin system:
3. Renin is the enzyme of the hydrolase class which will catalyze the cleavage of angiotensinogen to create angiotensin I.
4. Angiotensinogen is derived from the liver and is alpha-2 globulin.
5. Angiotensin I is converted to angiotensin II in the lung where there is an abundance of the angiotensin-converting enzyme.
   1. Angiotensin II is the potent vasopressor agent responsible for the renal type of hypertension.
   2. Angiotensin II also releases aldosterone from the adrenal cortex.
   3. Angiotensin II + aldosterone both leads to :
      1. Hypertension.
      2. Increase in the blood volume.
      3. Serum sodium.

5. The Renin+aldosterone regulate:
   1. Sodium and potassium balance.
   2. Blood pressure.
   3. Blood volume.
6. Renin is released when there is:
   1. Low plasma volume.
   2. Low blood pressure.
   3. Low sodium.
   4. Increased Potassium.
7. Renin release is suppressed when there is:
   1. Loss of potassium.
   2. Increased blood volume.
   3. An acute increase in blood pressure.
8. Renin value increases when the position changes from the recumbent to upright.
   1. High sodium intake decreases the renin level.
9. The measurement of plasma renin activity is used in the differential diagnosis of hypertension.
10. 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.

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:

1. Secondary aldosteronism with malignant hypertension.
2. Chronic renal failure.
3. Renovascular hypertension.
4. Salt losing status due to GI diseases.
5. Renin producing tumor of the kidney.
6. Pheochromocytoma.
7. Few patients with essential hypertension around 15%.
8. Reduced plasma volume due to low sodium.
9. Drugs like diuretics.
10. Addison disease.
11. Cirrhosis.
12. Hyperkalemia.
13. Hemorrhage.

Decreased Renin level is seen in:

1. Unilateral renal artery stenosis.
2. Primary aldosteronism (98%).
3. Congenital adrenal hyperplasia with 17- hydroxy deficiency.
4. Administration of salt-retaining steroids.

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