Chemistry, toxicology & urinalysis
Organ specific
Adrenal
Aldosterone
Author: Renu Virk, M.D.
Last author update: 1 January 2010
Last staff update: 2 April 2020
Copyright: 2002-2023, PathologyOutlines.com, Inc.
PubMed Search: Aldosterone [title] adrenal
Table of Contents
Definition / general | Pathophysiology | Clinical features | Laboratory | Additional referencesCite this page: Virk R. Aldosterone. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/chemistryaldosterone.html. Accessed March 22nd, 2023.
Definition / general
- Hormone that increases the reabsorption of sodium and water and the release (secretion) of potassium in the kidneys
- This increases blood volume and, therefore, increases blood pressure
Pathophysiology
- Synthesized and released into bloodstream by zona glomerulosa of the adrenal gland
- Average daily production is 0.1 to 0.7 μml (50 to 250 μg) with normal salt intake
- Inactivated in liver by conjugation with glucuronic acid or sulfuric acid
- Secretion is regulated by renin-angiotensin system (main regulator), serum potassium concentration and ACTH levels
- Decrease in effective circulating blood volume increases aldosterone via renin-angiotensin axis
- Increase in serum potassium increases aldosterone levels
- ACTH plays a minor role in regulation of aldosterone synthesis
- Aldosterone secretion in healthy subjects is increased by low-salt diet (< 2 gm/day), stress, upright posture and diuretic therapy, and is decreased by high salt diet or lying supine (lying down with face up)
Clinical features
Function:
- Major regulator of effective circulating blood volume
- Increases renal reabsorption of sodium and water to maintain blood pressure and tonicity
- Acts through mineralocorticoid receptors in renal cortical collecting ducts
- Also increases urinary excretion of potassium and hydrogen ions
- Recently discovered to have an effect on endothelium and coronary relaxation (Pharmacol Rep 2009;61:58)
Laboratory
Methodology to measure levels:
Specimen collection:
Indications for serum or urine aldosterone testing:
Limitations:
Reference ranges:
Interpretation:
- Radioimmunoassay (RIA) is most common method
- Extraction of aldosterone from plasma or urine followed by chromatography is done if levels of deoxycorticosterone or cortisterone are high, as antialdosterone antibodies may cross-react with them
- Note: It is important to control the time of sampling, posture and dietary sodium while collecting the sample
- Ideally sample should be obtained at 8 am after 4 hours of lying down (recumbency) and on unrestricted salt diet
Specimen collection:
- Urine or serum
- Same laboratory methods can be used for both specimens, except that urine is acid hydrolyzed before assay
- 24 hr urine sample is ideal specimen - urine is collected with boric acid as preservative
- Urine is acidified by adding acetic acid
- Urine aldosterone is measured in the form of 18-glucuronide by radioimmunoassay
Indications for serum or urine aldosterone testing:
- To diagnose hyperaldosteronism
- To differentiate aldosteronoma from idiopathic hyperaldosteronism
Limitations:
- Isolated serum aldosterone measurement has little clinical value
- Serum aldosterone levels should be interpreted in conjunction with plasma renin activity and serum potassium concentration
- Note: Urine aldosterone measurement is more useful clinically than random plasma aldosterone levels
Reference ranges:
- Plasma aldosterone, supine position and normal sodium diet: 2-9 ng/dl (55 - 250 pmol/L)
- Plasma aldosterone, upright position (standing / seated for at least 2 hr) and normal sodium diet: 2 - 5x supine value
- Urine aldosterone: 5 - 20 μmg/24 hr (14 - 56 nmol/24 hr)
- Conversion factor: multiply by 0.0277 to convert from ng/dl to nmol/L
Interpretation:
- High values: primary hyperaldosteronism, aldosterone secreting adrenal tumor, idiopathic adrenal hyperaldosteronism
- Low values: adrenal insufficiency, congenital adrenal hyperplasia due to 11-beta-hydroxylase deficiency
Additional references
