investigation

Last edited 08/2021 and last reviewed 05/2022

Preliminary investigations:

• hypokalaemia*- ensuring absence of diuretics, steroids, laxatives
• hypernatraemia - sodium may be mildly elevated or normal
• metabolic alkalosis

Special investigations:

• plasma renin and aldosterone - low renin and high aldosterone (raised aldosterone: renin ratio) suggests primary hyperaldosteronism - note that a normal or high renin may occur secondary to compensatory mechanisms
  • assess the effect of posture on renin, aldosterone and cortisol (measure at 9am lying and at noon standing) - this provides further information as to the cause of primary hyperaldosteronism
    • if reduced aldosterone and reduced cortisol on standing then ACTH dependent cause e.g. adrenocortical adenoma (Conn's syndrome)
    • if increased aldosterone and reduced cortisol then angiotensin-II dependent cause e.g. bilateral adrenocortical hyperplasia
• 24 hour urinary aldosterone - raised in primary disease

Distinction between adenoma and hyperplasia:

• CT scan - a unilateral adrenal mass suggests adenoma
• adrenal vein sampling:
• in bilateral adrenal hyperplasia the aldosterone:cortisol ratio is higher in each adrenal vein than in the inferior vena cava
• in unilateral adenomata the aldosterone:cortisol ratio is higher in the adrenal vein draining the adenoma than in IVC; the ratio is reversed in the contralateral adrenal

• measure plasma aldosterone 9 am after overnight recumbency and then at 12 pm after patient has been up and about:
• hyperplastic adrenals respond to angiotensin II which increases over the morning resulting in higher aldosterone at 12 pm
• adrenal adenomata respond to ACTH which is higher at 9 am resulting in lower aldosterone at 1200 pm

* there is an increasing frequency in the diagnosis of primary aldosteronism (1):

• principal reason for the increasingly frequent diagnosis of this disease, once viewed as rare, is that normokalemic Conn's syndrome is now recognized as an independent disease entity
• normal serum potassium may be present in up to 38% of patients, especially in patients with adrenal hyperplasia or familial aldosteronism
• found in 5% to 18% of patients with high blood pressure

Reference:

• Aronova A, Fahey TJ III, Zarnegar R. Management of hypertension in primary aldosteronism. World J Cardiol. 2014 May 26;6(5):227-33