Detecting patients with Cushing's syndrome: The importance of initial test selection

BACKGROUND AND OBJECTIVES

The recommended initial tests for suspected Cushing's syndrome are late-night salivary cortisol (LNSC), 24-hour urinary free cortisol (UFC) and the 1 mg overnight dexamethasone suppression test (ONDST). These tests have higher sensitivity and specificity than serum cortisol. The aim of this study was to determine the relative frequency of these requested tests in primary care.

METHOD

Initial test selection for investigation of Cushing's syndrome was audited by reviewing pathology request forms for cortisol tests made to a major community-based laboratory in 2019. Those with hypertension or adrenal incidentaloma as the documented indication for testing were included.

RESULTS

In 214 of 272 cases (78.7%; 95% confidence interval: 73.2%, 83.3%) initial testing was by measurement of serum cortisol alone.

DISCUSSION

The relatively infrequent selection of the higher sensitivity tests (ONDST, UFC and LNSC) for investigation of suspected Cushing's syndrome signifies a risk of delayed or missed diagnosis, with important implications for morbidity and mortality.

Approach to the diagnosis of secondary hypertension in adults

Presentations that should raise suspicion of secondary hypertension include early-onset, severe or resistant hypertension. A suggestive family history or clinical clues can point to a specific secondary cause. The most common causes and associations are renal disease, primary aldosteronism and obstructive sleep apnoea. Medicines, illicit substances and alcohol may also be responsible. The assessment of patients begins with history taking and examination, to look for clinical clues. Laboratory tests include electrolytes, urea, creatinine and the aldosterone:renin ratio, urinalysis and the urine albumin:creatinine ratio. Abnormal results should prompt further investigation. Initial testing for primary aldosteronism is best done before starting potentially interfering antihypertensive drugs. If the patient is already taking interfering antihypertensive drugs that cannot be stopped, the interpretation of the aldosterone:renin ratio must consider the presence of those drugs. Specialist advice can be sought if needed.