Blood Sciences Test
Aldosterone and Renin Activity
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
