In the diagnosis of primary aldosteronism or similar forms of hypokalaemic hypertension.
In localising the aldosterone adenoma by adrenal vein catheter sampling.
In certain types of adrenocortical insufficiency - particularly hypoaldosteronism or other salt wasting disease associated with abnormalities of steroid biosynthesis.
In cases of hypokalaemia query cause, eg Bartters syndrome.
Hyporeninaemic syndromes producing hyperkalaemia.
Note: Renin measurement is indicated in most of the above applications.
Interpretation of adrenal vein aldosterone levels require simultaneous central (adrenal vein) and peripheral sampling for cortisol and aldosterone levels. Constant low dose ACTH stimulation may assist interpretation of results. Please consult with an Endocrinologist before undertaking adrenal vein sampling tests. Remember that prior drug use (eg. spironolactone, amiloride, ACE inhibitors, AT2 antagonists, beta blockers and diuretics) may affect interpretation of aldosterone and renin results.
Patient's posture, salt intake, drug therapy, age and time of sampling affect levels. Potassium depletion and/or hypokalaemia lower renin - aldosterone secretion.
Outpatients are best screened as follows: If possible stop non-essential anti-hypertensives for 2 weeks before sampling. Many hypotensive drugs alter renin - aldosterone levels; preferred agents are Alpha-blockers (Doxazosin, Prazosin) and non-dihydropyridine calcium channel blockers (Verapamil, Diltiazem) since they do not greatly alter renin - aldosterone. Screening tests for primary hyperaldosteronism and related conditions can still be done in patients on betablockers, ACE inhibitors and/or diuretics, BUT interpretation must allow for the potent effects these drugs have on the renin - aldosterone axis. Patients should attend (non-fasting) prior to 10.00 am for "ambulant sampling of plasma aldosterone and renin. It is usually wise to check plasma Na, K and creatinine at the time of sampling.
Inpatients are screened as above and should be ambulated for at least 30 minutes before sampling.
Other protocols involving plasma aldosterone/renin measurement include saline suppression (2L saline over 4 hours), 4-hour posture test (08.00 overnight supine aldosterone, repeated after 4 hr of upright posture) and tests using ACTH stimulation or dexamethasone suppression.
If patient is on high dose Biotin therapy (>5 mg/day), wait until at least 8 hours after last dose to take blood sample.
Specimen Collection Protocols:
EDTA blood collected and centrifuged at room temperature. Whole blood EDTA is stable for 8 hours at room temperature. Separated EDTA plasma is stable for 5 hours at room temperature.
Plasma stored and transported deep-frozen. Thawed samples will not be assayed. If Renin or Aldosterone - Renin ratio is required, preferably collect blood before 10 am.
For aldosterone alone 1.5 ml EDTA blood (1.2 ml paediatric).
If overnight - Frozen
DO NOT STORE OR TRANSPORT AT 4oC to prevent cryoactivation of prorenin
Interpretation depends on renin status. Plasma Aldosterone-Renin ratio greatly assists in diagnosis.
High plasma aldosterone levels occur in primary aldosteronism, where the aldosterone/PRA ratio is >30.5 (pmol/L)/(mIU/L) (Adult) using Endolab methods. Note that hypokalaemia could affect interpretation, since aldosterone secretion is reduced by potassium depletion. High values may also occur in secondary hyper-aldosteronism, in sodium depletion and in many oedematous disorders and in these states Renin is usually elevated.
Low plasma aldosterone levels – hypoaldosteronism, hyporeninaemia syndromes, (eg non-aldosterone dependent forms of hypermineralocorticoidism), Addison’s disease and some forms of congenital adrenal hyperplasia. Low values may also occur in normal subjects receiving liberal salt intakes, and in the aged (>60 years).
Details regarding drug therapy, time of sampling, and posture are necessary for interpretation.
Table to be inserted ???
Age affects aldosterone levels. Values are higher in very young children and lower in subjects over 60 yrs. Plasma aldosterone values are likely to be unreliable in severe renal failure, including patients on dialysis.
4hr Saline Loading for Hyperaldosteronism
07.00 – 10.00 Ambulant (adult): 103 – 1197 pmol/L
07.00 – 10.00 Supine (adult): 103 – 859 pmol/L
$40.90 (Exclusive of GST)