Newcastle Laboratories

Aldosterone, plasma

Clinical Background:

Aldosterone is the principal mineralcorticoid secreted by the zona glomerulosa of the adrenal cortex and is a potent regulator of electrolyte secretion. The interaction of aldosterone, renin and an...

Aldosterone is the principal mineralcorticoid secreted by the zona glomerulosa of the adrenal cortex and is a potent regulator of electrolyte secretion. The interaction of aldosterone, renin and angiotensin is important in the regulation of extracellular fluid volume, blood pressure and the balance of sodium and potassium ions.
The major application of the measurement of aldosterone is in the investigation of primary hyperaldosteronism. Primary hyperaldosteronism (also known as Conn’s syndrome) can be defined as the inappropriate hypersecretion of aldosterone in the absence of activation of the renin-angiotensin system. Overproduction is usually due to autonomous production by an adenoma or hyperplasia in both adrenals (idiopathic adrenal hyperplasia) but can also be due to adrenal carcinoma or familial glucocorticoid-suppressible aldosteronism.

The aldosterone to renin ratio (ARR) is considered the best first line investigation of suspected hyperaldosteronism. However, the ARR is influenced by a range of factors and appropriate patient preparation and potentially interfering medications should be accounted for.

The ARR is considered to be a screening or case-detection test, rather than diagnostic due to its limited positive predictive value. Confirmatory testing (e.g. saline infusion test, fludrocortisone suppression test) is recommended in cases where the ARR is raised. These tests involve measurement of plasma aldosterone to determine if appropriate suppression has occurred.

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Test Details

  • Discipline:

    Biochemistry

    Biochemistry

  • Specimen Container Adult:

    Plasma-EDTA

    Plasma-EDTA

  • Specimen Container Paediatric:

    Plasma-EDTA

    Plasma-EDTA

  • Minimum Volume Adult:

    3 mL blood

    3 mL blood

  • Minimum Volume Paediatric:

    2 mL blood

    2 mL blood

  • Special Requirement:

    Please include details of any hypertensive medication as this may affect interpretation of the aldosterone/renin ratio (ARR). Endocrine Society Guidelines recommend the following patient preparatio...

    Please include details of any hypertensive medication as this may affect interpretation of the aldosterone/renin ratio (ARR). Endocrine Society Guidelines recommend the following patient preparation:

    Attempt to correct any underlying hypokalaemia.

    Encourage liberal (rather than restricted) sodium intake.

    Withdraw agents that markedly affect ARR for at least 4 weeks (e.g. spironolactone, amiloride, K-wasting diuretics).

    Withdrawal of other agents should be considered in cases of a non-diagnostic ARR and if hypertension can be controlled on relatively non-interferring medications.

    Blood should ideally be collected mid-morning after the patient has been ambulant for at least 2 hours and then seated for 5-15 minutes.

    If renin has also been requested, note that the sample should not be stored at refrigerator temperature at any point (to avoid cryo-activation of renin) and should be separated immediately on receipt and stored frozen.

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  • Sample Stability:

    Unseparated: Same day (6 hrs if renin requested)
    Separated: 4 days at 4-8°C (unless renin requested), 1 month at -20°C

    Unseparated: Same day (6 hrs if renin requested)
    Separated: 4 days at 4-8°C (unless renin requested), 1 month at -20°C

  • Transport Requirements:

    Ambient (frozen if renin requested)

    Ambient (frozen if renin requested)

  • Interpretation:

    The ARR cut-off for exclusion of primary aldosteronism is 30 pmol/mIU. In addition to a raised ARR the aldosterone concentration should also be taken into account. Aldosterone is typically >400 pmo...

    The ARR cut-off for exclusion of primary aldosteronism is 30 pmol/mIU. In addition to a raised ARR the aldosterone concentration should also be taken into account. Aldosterone is typically >400 pmol/L in primary aldosteronism, although an aldosterone between 250 and 399 pmol/L has been reported in some cases.

    It is important to take into account possible effects of anti-hypertensive medication that can alter the ARR. Some medications may raise the ARR (e.g. beta-blockers, NSAIDs, central alpha-2 agonists) or lower it (e.g. diuretics, ACEi, ARB, dihydropyridine Ca channel-blockers) potentially leading to false positives or false negatives, respectively.

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  • Reference Ranges:

    Upright: 103 to 1197 pmol/L
    Supine: 103 to 859 pmol/L

    Upright: 103 to 1197 pmol/L
    Supine: 103 to 859 pmol/L

  • Factors Affecting Result:

    Gross haemolysis, icterus or lipaemia may interfere.

    N.B. Heterophilic antibodies can interfere with immunoassays.

    Gross haemolysis, icterus or lipaemia may interfere.

    N.B. Heterophilic antibodies can interfere with immunoassays.

  • Routine Contact Name:

    Duty Biochemist

  • Routine Telephone:

    Freeman: 0191 244 8889

    RVI: 0191 282 9719

    Freeman: 0191 244 8889

    RVI: 0191 282 9719

  • Routine Email:

    - For external users: TNU-Tr.duty.biochemist@nhs.net

    - For Trust users: DutyBiochemist@nuth.nhs.uk

  • Specialist Test:

    Yes

    Yes

  • Specialist Contact Name:

    Endocrine Lab

    Endocrine Lab

  • Specialist Telephone:

    0191 282 4025

    0191 282 4025

Availability:

Available during full access hours
Assayed weekly
Site of analysis: RVI

Turn Around:

Within 2 weeks

Send To:

Department of Blood Sciences 
Level 3
Leazes Wing
Royal Victoria Infirmary
Queen Victoria Road
Newcastle upon Tyne
NE1 4LP

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