How to make a lab diagnosis of Cushing’s syndrome (CS)

When should we investigate for Cushing’s syndrome CS? Remember it is a laboratory diagnosis. the symptoms and signs are non-specific and there can be a lot of overlap in patients being treated with steroids of which the indications are becoming more and more common and diverse: kidney and other organ transplants, asthma, sometimes COPD, autoimmune diseases like SLE, Polymyalgia rheumatica, giant cell arteritis, rheumatoid in short bursts, part of the chemotherapy of lymphoma. You get the idea right?

The most common cause of hypercortisolism is ingestion of prescribed glucocorticoid, usually for nonendocrine disease. However, CS can also be caused by other oral, injected, topical, and inhaled glucocorticoids  and by high doses of megestrol acetate or other progestins with some intrinsic glucocorticoid activity. Megestrol acetate is a progestin; is an antineoplastic agent; is a hormone and an appetite stimulant. It is used orally in cancer of the breast, endometrium, anorexia associated with HIV/AIDS and cancer cachexia.

If you are dealing with HIV/AIDS then think of ritonavir. The clearance of some inhaled or injected steroids may be delayed by ritonavir, which inhibits CYP3A4 metabolism of many glucocorticoids, leading to CS.

CS may also be caused by the use of glucocorticoid-containing creams or herbal preparations so beware the hakim sahib and his drugs.

So when should we look for CS? When I was working in the Army at the start of my career every soldier in active service who was found to be hypertensive would be investigated for CS. A 24 hour urinary free cortisol level and serum cortisol level were mandatory. Our awareness of chronic kidney disease was almost zero. Over the decades it became apparent that we were wasting too many lab resources and the trends changed. We checked the levels of serum urea and creatinine or if we were being very clever, the creatinine clearance and kidney size before we checked the hormone levels.

So look for CS if there is refractory hypertension in a young person or hypertension and osteoporosis in a young person. Severe refractory hypertension in patients of any age is a good starting point, specially if there is severe osteoporosis. Then of course there is obesity with red striae at least a cm wide, hirsutism, a round face. Then beware of an ultrasound or other image which says “likely to be an enlarged adrenal gland or a small mass in the adrenal gland. These are “incidentalomas” which you happened across and must investigate.

Initial testing.

A. Use 2 very sensitive tests to start your diagnosis. (You can spend the next 3 months convincing the patient that they do not have the disease).

  • low index of suspicion:  initial testing with one of the following first-line tests:
    • late-night salivary cortisol (two measurements),
    • 24-hour urinary free cortisol (UFC) excretion (two measurements), 
    • the overnight 1 mg dexamethasone suppression test (DST).

For example, a woman with oligomenorrhea and hirsutism might be tested for CS; however, the pre-test probability of the syndrome is low if there are no other associated signs or symptoms. She is more likely to have polycystic ovaries specially if there is infertility.

  • For high index of suspicion (you have excluded exogenous steroid intake and the patient is obviously cushingoid not just obese),  optimize sensitivity, by using the upper limit of the reference range for UFC and salivary cortisol and a serum cortisol concentration <1.8 mcg/dL (50 nmol/L) after dexamethasone as the cutoffs for a normal response.
    • If  you choose UFC  as the initial screening test, the result should be unequivocally increased (threefold above the upper limit of normal for the assay) or the diagnosis of CS is uncertain and other tests should be performed.
    • Or you can use use the longer low-dose DST (2 mg/day for 48 hours) as an initial test.
    • UFC and late-night salivary cortisol measurements are each obtained at least twice because the hypercortisolism in CS may be variable Roghly 84% specific). Two measurements must be abnormal for the test to be considered abnormal; for patients with mild or fluctuating disease, this may require collecting a number of salivary cortisols or UFCs over weeks.

    • Normal results — If initial testing is normal in an individual with a low index of suspicion for CS, it is unlikely that the patient has CS unless it is extremely mild or cyclic. Do not do  additional evaluation unless symptoms progress or cyclic CS is suspected. In this case, referral to an endocrinologist for repeat testing and further evaluation is indicated.

  • Exclude physiological hypercortisolism. This is seen in:
    • Pregnancy, patients with severe obesity, especially those with visceral obesity or PCOS, patients with psychological stress, especially patients with a severe major depressive disorder and melancholic symptoms, poorly controlled diabetes mellitus, rarely, chronic alcoholism

  • Patients who are unlikely to have hypercortisolism include

    physical stress (illness, hospitalization/surgery, pain), malnutrition, anorexia nervosa, intense chronic exercise, hypothalamic amenorrhea, high corticosteroid-binding globulin (CBG) (increased serum cortisol but not UFC), glucocorticoid resistance. There is no need to test them for CS.

  • Patients with severe liver dysfunction, may have transiently increased secretion of corticotropin-releasing hormone (CRH) or impaired hypothalamic or pituitary responsiveness to cortisol. However, their peripheral and petrosal sinus plasma CRH concentrations are normal, although these tests are not clinically indicated. The changes revert to normal after 3 weeks of abstinence.
  • Beware of anomalies. For example, a late-night salivary cortisol test is likely to be abnormal in a shift worker, and a dexamethasone suppression test (DST) response may be abnormal in a woman taking oral estrogen, because of increased corticosteroid-binding globulin (CBG) (and hence total cortisol). These tests would not be ideal and other tests would be chosen based on the individual’s history and lifestyle.
  • Why is UFC reliable? Twenty-four-hour urinary cortisol excretion provides a direct and reliable practical index of cortisol secretion because corticotropin (ACTH) and cortisol are secreted in discrete bursts, not only in normal subjects but also in most patients with Cushing’s disease.

HAve you found the answers?

  • Whom should we investigate for CS?
  • How specific is a late night salivary cortisol level? When is it likely to be incorrect?
  • If you get normal levels initially in all the tests when will you decide that you need to do the tests again?
  • What is polycyclic CS?
  • What is physiological hypercortisolism?
  • In which patients are you likely to find hypercortisolism?
  • What drugs other than steroids can cause hypercortisolism?
  • What drug can you use for anorexia of AIDS and cancer?
  • When is a 2 mg dexamethasone test performed?
  • Why is a UFC better than serum free cortisolism?

B. Try and establish the cause. I have copied an algorithm from UptoDate for your convenience.

Testing to establish the cause of Cushing’s syndrome
ACTH: corticotropin; CRH: corticotropin-releasing hormone; CT: computed tomography; MR: magnetic resonance; MRI: magnetic resonance imaging; dex: dexamethasone; IPSS: inferior petrosal sinus sampling.
* Testing can only be interpreted in the context of sustained hypercortisolism and may be inaccurate with cyclic hypercortisolism.







Published by


I am a Professor of Medicine and a Nephrologist. Having served in the Army Medical College, Pakistan Army for 27 years I eventually became the Dean and Principal of the Bahria University Medical and Dental College Karachi from where I retired in 2016. My passion is teaching and mentoring young doctors. I am associated with the College of Physicians and Surgeons Pakistan as a Fellow and an examiner. I find that many young doctors make mistakes because they do not understand how they should answer questions; basically they do not understand why a question is being asked. My aim is to help them process the information they acquire as part of their education to answer questions, pass examinations and to best take care of patients without supervision of a consultant. Read my blog, interact and ask questions so that I can help you more.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s