Aldosterone

Diagnostic Use

Aldosterone is the predominant mineralocorticoid hormone and has an important role in intravascular volume regulation. The renin-angiotensin-aldosterone system is activated in response to low plasma volume. Biological actions of aldosterone include renal sodium and water retention, renal potassium and hydrogen ion excretion and arterial vasoconstriction.

Aldosterone is usually requested with a paired renin request, and results may be interpreted as the aldosterone renin ratio (ARR). Most commonly, the ARR is requested as a screening test for primary aldosteronism. Further diagnostic tests for primary aldosteronism include the saline suppression test and adrenal vein sampling - both of these tests also rely on aldosterone measurement.

Rarer indications for aldosterone measurement include investigation of conditions associated with mineralocorticoid deficiency (hypoaldosteronism) and resistance (pseudohypoaldosteronism) and in the investigation of certain renal tubular disorders (e.g. Bartter and Gitelman syndromes).

Aldosterone measurement is not routinely recommended for the diagnosis or monitoring of primary adrenal insufficiency; plasma renin is preferred for assessment of mineralocorticoid replacement

Department

Endocrinology Lab

Delphic Registration Code

ALD

Laboratory Handling

Phlebotomy

Please collect one full EDTA tube dedicated to this test.

Registration

Please register separately to plasma metanephrines (often requested together).

Separating

Samples should be separated within 6 hours and frozen at -20C.

Laboratory

Samples should be separated within 6 hours and frozen at -20C.

Test Adds

Not available.

Turnaround Time

7 days

Test Code

8376

Specimen Type

• Plasma

Specimen Requirements

Tube/Container Type:

Preferred

• EDTA (Lavender Cap)

Preferred Sample Volume (ml)

5

Minimum Sample Volume (ml)

1.5

No of Samples Required

1

Paediatric Specimen Requirements

Tube/Container Type:

Preferred

• EDTA (Lavender Cap)

Preferred Sample Volume (ml)

5

Minimum Sample Volume (ml)

1.5

Pre-testing Requirements

Many pre-analytical factors can affect plasma aldosterone levels. It is important to prepare a patient for aldosterone testing so that the result may be interpreted with confidence:

Posture and timing
The specimen should be collected in the mid-morning after the patient has been ambulant for at least 2 hours

The specimen should be collected after the patient has been seated for at least 5 minutes

Interfering medications
Many antihypertensive medications interfere with plasma aldosterone levels and may lead to falsely low or high ARR results.

ACE inhibitors, angiotensin receptor blockers, beta blockers and centrally acting alpha-2 antagonists (e.g. clonidine) all suppress aldosterone, although beta blockers and alpha-2-antagonists may falsely elevate the ARR due to a greater suppressive effect on renin levels.

Diuretics and aldosterone receptor antagonists will increase plasma aldosterone.

Ideally patients on potentially interfering medications should have their medications changed to non-interfering drugs for at least 4 weeks before testing takes place. Non-interfering antihypertensives include peripherally acting alpha-antagonists (e.g. doxazosin) and non-dihydropyrimidine calcium channel blockers (e.g. diltiazem).

Impact of potassium and sodium status
Hypokalaemia will suppress aldosterone production. Patients with hypokalaemia should receive adequate potassium replacement before measuring the ARR.

Dietary sodium restriction will stimulate aldosterone production. Patients should not restrict salt intake in the days leading up to testing

Impact of the menstrual cycle
If possible, ARR testing should take place during the follicular phase of the menstrual cycle (i.e. days 1-14) as aldosterone and renin increase during the luteal phase of the cycle and results may be less reliable

Additional Specimen Information

Paired aldosterone and renin samples have different storage and transport requirements. Please refer to the test guide entry for renin for more information.

Separate tubes are required for renin and aldosterone testing.

Aliquot Instructions

Sample Type

• Plasma

Minimum Volume (ml)

1

Transport to Lab

Frozen
If overnight - Frozen

Additional Referral/Aliquot Information

Separate within 6 hours and freeze at -20C as soon as possible.
Rural collection sites without the ability to separate and freeze plasma and transport frozen samples should consider sending patient to a main centre for collection to ensure sample integrity.

Interpretation

Interpretation of the aldosterone-renin ratio (ARR)

An ARR >50 pmol/mIU is supportive of, but not diagnostic of primary aldosteronism (PA).  In PA, the renin is usually suppressed and the aldosterone is usually inappropriately elevated relative to the renin concentration (e.g. >200pmol/L).

An ARR of 30-50 pmol/mIU is considered an equivocal result.  Patients with an ARR in this range may require further testing, particularly if there is a higher pre-test probability of primary aldosteronism.

An ARR of <30 pmol/mIU is makes primary aldosteronism unlikely, assuming that the correct pre-analytical processes were followed (see section above on pre-testing requirements).

An ARR is a screening test only.  Positive results often require a further diagnostic test, particularly if the patient is a candidate for potentially curative surgery.

The ARR is an imperfect screening test.  It is reasonable to repeat the ARR in cases of ongoing diagnostic uncertainty regardless of the initial result.

Interpretation of the saline suppression test

A post-infusion aldosterone >160 pmol/L (after infusion of 2L of 0.9% saline over 4 hours) is supportive of primary aldosteronism.

Interpretation of aldosterone in other settings

In rarer clinical settings (e.g. suspected hypoaldosteronism or pseudohypoaldosteronism), consultation with a chemical pathologist or specialist clinician is recommended if assistance is required in interpreting an aldosterone result.

Reference Intervals

Reference intervals are not reported for this test

See above for information on interpretation.

Test Method

LC-MS/MS

Non-Funded Test Cost

$49.73 (Exclusive of GST)

Billing Code

8376

Contact Information

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