If a patient has an autoimmune arthritis like rheumatoid arthritis for example, and he did not respond to the initial conventional medications that we also call non-biologic medications, in that case we shift to one of the biologic medications as they are more potent. The question here is: why do rheumatologists request a tuberculosis test, called the TB test, for those patients who will start a biologic medication? And if the test result came out positive, does that mean that our patient who has rheumatoid arthritis also has tuberculosis and we discovered it by chance?
We will start with some info about the TB test and how we interpret its result and then we will explain the connection between this test and prescribing a biologic medication.
If the TB test is positive, this is the more significant result for the doctor and the patient. A positive test means the patient had been exposed to the tuberculosis organism at some point in time before and that’s why the immune system kept it in its memory. This is what positive test means.
And if the patient’s immune system has been exposed to the tuberculosis organism, this means one of two things:
First: the patient has an immunity to the TB organism but does not have the disease. This is the more common reason for a positive test by the way.
Second: the patient does have the disease and we discovered it by chance while doing the test.
How do we sort out if the positive test means he only has immunity but not the disease from having the disease?
We do a chest X ray any way for all patient to look for evidence of tuberculosis if any, and we also ask more questions during our history taking from the patient and we do the needed relevant clinical examination to exclude tuberculosis.
If the patient is confirmed to have active tuberculosis disease, this will be quite exceptional and the patient will be referred for management of tuberculosis.
But almost all patients with a positive test will belong to the group who have immunity only to tuberculosis, not active disease.
Now let me tell you something that is so peculiar about how the body makes that immunity to the tuberculosis organism as it is the very reason for the connection with biologic medication prescriptions.
The tuberculosis organism is a weak organism and indeed many of us get exposed to it at some point in time. But because it is a weak organism, the immune system inactivates it and makes a wall to surround it and it stays within the confines of that wall forever in an inactive or dormant form.
Should our immunity become weakened for any reason later on some day, maybe this weak organism might get activated to cause the disease tuberculosis.
Now how is this tuberculosis test and tuberculosis story related to biologic medications?
There are certain biologic medications, namely the biologic medications that target and downregulate an inflammatory mediator in the body called tumor necrosis factor or TNF; we use those medications for the control of the inflammation in patients with some autoimmune arthritis like rheumatoid arthritis, ankylosing spondylitis or psoriatic arthritis. The point is that this tumor necrosis factor, also, at the same time, is the very part of the immune system that makes sure that the TB organism stays dormant and confined in an active form. So, if we target this TNF with our anti-TNF biologic medications, there might be a chance that the TB organism gets activated and causes the tuberculosis disease.
For that reason, it is agreed among the different authorities that if a patient with an autoimmune arthritis has a positive TB test that is confirmed to be mere exposure and immunity to the organism and not active tuberculosis, and if that patient will be prescribed an anti-TNF biologic medication, in that case we will start the patient on prophylactic anti-TB medications for a few months and we will delay the start of the biologic medication for a couple of weeks and then start it.
So, this is the connection between the TB test and the biologic medications.
It is important to note here that there are other biologic medications that do not really target the parts or the mediators in the immune system that would contribute to TB reactivation. Nevertheless, the guidelines for TB testing and possible prophylactic anti-TB treatment were extended to also include those medications to be on the very safer side.
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This post was prepared and published by Dr. Hatem Eleishi. Dr. Hatem Eleishi is a professor of rheumatology at Cairo university (Egypt) and is especially dedicated to supporting arthritis patients with online educational videos and articles about arthritis causes and treatment. He also runs a rheumatology clinic in Cairo and a center for www.tabibakom.com/en that, in addition to providing online rheumatology consultations, also provides online medical consultations in several different medical specialties by expert consultants from Egypt, Canada and the United States.
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