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