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Aldosterone and Renin Activity

Blood Sciences Test


Specimen

EDTA

Taken from

Endocrinology Handbook

Endocrine Unit

Imperial College Healthcare NHS Trust

Charing Cross, Hammersmith and St. Mary’s Hospitals

Updated: March 2010

INDICATIONS

  • Accelerated hypertension.
  • Drug resistant hypertension
  • Hypertension and adrenal incidentaloma
  • Hypertension with hypokalaemia, spontaneous or easily provoked, i.e. by diuretics or sodium loading – consider if plasma potassium is <3.6 mmol/L. As the treatment of hyperaldosteronism is far more effective in correcting hypokalaemia rather than the hypertension extensive investigation in normokalaemic patients is not justified.

CONTRAINDICATIONS.

None

SIDE EFFECTS

None

First Line Investigation OF PRIMARY HYPERALDOSTERONISM (CASE DETECTION):

It is important to remember that normokalaemic hypertension constitutes the most common presentation of this disease. Therefore, hypokalaemia alone has a low positive predictive value for primary hyperaldosteronism.

Random plasma aldosterone/renin ratio

Outpatient procedure

Stop beta blockers for 2 weeks prior to the sample, as beta blockers prevent renin release and stop spironolactone 6 weeks before sample.

Other drugs need not be stopped unless further investigations are required (see below)

Supply details of all therapy on request form

Ensure adequate salt intake – NOT loading

Correct severe hypokalaemia (<3.0 mmol/L) first, as a low potassium directly will reduce aldosterone secretion.

Method

Sit patient quietly for at least 10 minutes

1 X EDTA samples (7.5 ml red top)

Send to lab (must be received within 6 hr of sample collection). Do not send sample on ice.

Interpretation of results

Aldosterone/renin ratio

>2000          Conn’s likely if renin >0.3 pmol/mL/h

800 – 2000    Possibly Conn’s, investigate further

<800            Conn’s unlikely

For diagnosis of Conn’s: low renin expected

Plasma renin         ≤0.3 pmol/ml/hr      (ref. 0.5-3.1)

Aldosterone           usually > 350 pmol/L  (ref. 100-800) ie. may be normal or high

SECOND LINE INVESTIGATION: CONFIRMATION OF PRIMARY HYPERALDOSTERONISM

Saline infusion test:

Stop spironolactone and epelerone for 6 weeks before the test

Stop beta blockers, calcium channel antagonists, ACE inhibitors and AT2 blockers for 2 weeks before the test.

Can continue to use alpha blockers to manage hypertension eg doxazosin

Ensure plasma K in normal range (ideally >4) prior to performing test

Examine patient for signs of cardiac failure. This test should not be performed in patients with severe uncontrolled hypertension, renal insufficiency, cardiac insufficiency, cardiac arrhythmia, or severe hypokalemia.

Patients stay in the recumbent position for at least 1 hour before test begins.

Cannulate and take blood for plasma aldosterone, plasma renin activity, U and Es.

Infuse 2 litres of 0.9% saline over 4 hours, starting at 9.00 a.m. Blood pressure, oxygen saturation and heart rate are monitored throughout the test. After 4 hours (ie 13:00), take further blood sample for aldosterone, U and Es (IV saline infusion can promote hypokalaemia).

Interpretation

Principle of test is that the lack of suppression of aldosterone excretion with intravascular expansion indicates primary hyperaldosteronism.

Post-infusion plasma aldosterone levels <140 pmol/L (5 ng/dL ) make the diagnosis of primary hyperadosteronism  unlikely

Aldosterone levels  >280pmol/(10 ng/dL) are a very probable sign of primary hyperaldosteronism.

Values between 140 – 280 pmol/L (5 – 10 ng/dL) are indeterminate.

References:

Rossi GP et al Prospective evaluation of the saline infusion test for excluding primary hyperaldosteronism due to an aldosterone producing adenoma. Journal of Hypertension 25:1433-1442

Funder JW et al Primary hyperaldosteronism guidelines: Case detection, diagnosis and treatment of patient with primary hyperaldosteronism: An Endocrine Society Clinical Practice Guideline. JCEM Epub ahead of print Jun 13

Availability

Referred test

 

Specimen Labelling Procedure
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