There is a Blood Test for Depression!

A blood test, known as the Dexamethasone Suppression Test (DST) has been known for over 20 years, although not widely used.  The test is done by giving the patient with suspected depressive illness a once-off low dose (1 mg) of dexamethasone (a steroid medication) about 11 pm one night, and taking the blood for testing late the next afternoon or evening.  The level of cortisol (cortisone) in the blood is measured.  The person without depression responds to the presence of dexamethasone in their body by drastically reducing (suppressing) the amount of cortisol in their blood automatically, so their blood test shows low levels of cortisol.  However, in about 50 – 60% of people with depressive illness, their body ignores the presence of dexamethasone, and this blood test shows HIGH levels of cortisol the next day.  The failure to suppress cortisol production despite dexamethasone confirms the diagnosis of depressive illness. (Note to doctors: Normal suppression gives levels about 30-40 nmol/l. Levels above 140 after dexamethasone are normally regarded as a positive test indicative of depressive illness, in the absence of severe physical illness, enzyme inducing medications, high alcohol intake or hormonal illnesses)


We do not know why there are two different types of depressive illness, namely one type we can measure by this test, and one type (with identical clinical symptoms) we cannot measure in the laboratory.  Nor do we know why the DST is abnormal in some depressed patients while they are ill, returning to normal when they recover.


Your own physician or psychiatrist can discuss the benefits and limitations of this test in your particular case.  An abnormal DST is not enough evidence alone to diagnose depressive illness (physically ill, malnourished and elderly people have abnormal DST’s in about 20% of cases).  However, in people who are told their symptoms are due to unhappiness or due to unresolved emotional hang-ups, an abnormal DST is very good reason to suggest they have gone on to develop depressive illness, as a result of the stresses involved.


It must also be remembered that 50% of people with depressive illness still DO have the illness, although they respond normally on this test, just as some people have back pain without any abnormality showing on their X-rays.


Important Disclaimer:  This site is medical information only, and is not to be taken as diagnosis, advice or treatment, which can only be decided by your own doctor.


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