Conn's syndrome

Syndrome of hypertension and hypokalaemia caused by hyperaldosteronism. A diagnosis of Conn's may be caused by a unilateral adrenal adenoma or bilateral adrenal hyperplasia.

Baseline investigations - all patients

Full blood count

Useful indicator of general health and underlying disease.

Erythrocyte sedimentation rate

ESR is a useful indicator of underlying disease, particularly if there is clinical suspicion of renal or inflammatory disease.

Urea and electrolytes

Hypokalaemic alkalosis is seen in Conn's syndrome of any cause. It is important to document the severity of hypokalaemia when patients are off all treatments. If this is not possible, it is crucial to document all medications being taken at the time of any biochemical assessments.

Liver function test

Fatty liver is common in obesity, diabetes and Cushing's.

Bone profile

Useful indicator of general health and underlying disease.

Thyroid stimulating hormone

Untreated hyperthyroidism is associated with hypertension and can be associated with hypokalaemia in hypokalaemic periodic paralysis.

Fasting lipids, glucose, glycosylated haemoglobin

It is essential to stratify cardiovascular risk in all patients with hypertension.

Random recumbent renin and aldosterone

Recent guidelines suggest taking a baseline random renin and aldosterone to calculate ratio is a worthwhile initial screen even in the presence of interfering medications.

Assay methods, and units of measurement vary, but ratios above 800 using the units below, should prompt medication review and formal evaluation.

Aldosterone/renin ratio: 

>2000 Almost certainly Conn's
800-2,000 Possibly Conn's, investigate further
<800 Excludes Conn's

Plasma renin: 

Typically <0.5pmol/ml/hr (normal range 0.5-3.1)


Typically >250pmol/l (normal range 100-800)


ECG should be taken to assess cardiovascular status and seek end organ damage.

Chest radiograph

Chest XR should be taken to assess cardiovascular status and seek end organ damage.

Further investigations - selected cases only

Computerised tomography adrenals

After the biochemical diagnosis is confirmed, the adrenals should be imaged with CT scan prior to venous sampling. A typical Conn's adenoma is homogeneous with no clacification, has a smooth outline, has an attenuation coefficient Hounsfield unit (HU) value <10 or rapid washout of enhancement in those with HU>10.

Recumbent renin and aldosterone off all interfering medications

If the initial screening ratio is above 800, arrange for repeat assessment off all interfering medication as discussed in the management page.

Adrenal venous sampling

In patients over 50, non functioning adrenal adenomas are very common. In this group, lesions should be confirmed as functioning by performing selective venous sampling of both adrenals prior to considering surgery.

In patients under 50, if a unilateral adenoma is clearly visualised and the contralateral adrenal is clearly normal, sampling may not be necessary prior to surgery.

In all cases where both adrenals appear normal, or both appear bulky, sampling is required to determine whether disease is unilateral or bilateral.

Urinary free cortisol

Two 24 hour urinary collections for cortisol should be performed if Cushing’s is suspected. This is a sensitive but not specific initial screen for Cushing’s Syndrome.

Two normal results are reassuring if taken in conjunction with low probability of Cushing’s on thorough clinical assessment. This is also useful as it can be performed and interpreted in patients taking oestrogen containing medication such as the oral contraceptive pill.

However, this should never be considered as a screening test alone - multiple conditions lead to false positive results, for example obesity, depression, alcohol excess, and false negative results occur with cyclical and biochemically mild disease.

Other 24-hour urinary collections

24-hour urinary collection for sodium, potassium, protein, calcium or amino acid estimations should be considered where other causes of hypokalaemia are suspected such as Bartter's or Gitelman's syndromes.