Monitoring medication for IBD

Monitoring medication in Crohn's disease and ulcerative colitis

While you are taking medicines to treat your inflammatory bowel disease (IBD), you will need to be monitored by your IBD team. The monitoring usually takes the form of medical tests, such as blood tests.

There are several reasons why you will need to undergo regular monitoring. These include:

  • Checks to make sure the levels of the drug in your body are safe
  • Making sure you aren’t at risk of any unwanted side effects
  • Checking how your IBD is responding to your treatment

As well as having tests, your IBD team will also observe you, ask you about changes to your symptoms, and whether you are having any side effects during your treatment. 

There is a range of tests that are used to help monitor your treatment for Crohn's disease and ulcerative colitis. Which tests you have, and the frequency of these tests, will depend on the medication you are taking, your disease activity and any side effects you are experiencing.


Monitoring through blood tests

With certain medicines, you will have blood tests very regularly at first, becoming less regular as you continue your treatment. For example, when you begin treatment with azathioprine, it is recommended that you have monitoring blood tests weekly for the first four to eight weeks, and then tests at least every three months from then on1.

Things that may be looked at in your monitoring blood tests include:


During your treatment, blood tests will be used to check levels of inflammation in your blood, such as CRP. This will indicate whether your medicine is working effectively, whether your dose needs to be changed, or whether you might need an alternative treatment. 

Red and white blood cells

Some medicines that are used to treat IBD, such as thiopurines, can affect how your bone marrow works, and can reduce levels of red and white cells and platelets in your blood. These levels will be monitored throughout your treatment.

Liver and kidney function

Blood tests are also used to check that your liver and kidneys are tolerating your treatment, and effectively processing and removing the medicines from your body

Vitamins and minerals

Some medicines can affect how your body absorbs certain vitamins and minerals, such as calcium and folic acid. Tests can be used to monitor vitamin and mineral levels in your blood.

Levels of medication

Therapeutic drug monitoring blood tests are used to measure the concentration of the medicine in your blood. This is to check that the levels are within the therapeutic range - where the dose of medicine works most effectively whilst remaining safe. These tests are particularly important in medicines that have a narrow therapeutic index - this means they have a smaller difference between doses that are beneficial and harmful.

The timing of these blood tests is important. After taking a dose of your medicine the amount in your blood rises for a while, peaks, and then starts to fall, reaching its lowest level just before your next dose. For your medicine to be as effective as possible, the peak level and the lowest level should remain within the therapeutic range. If not, changes to the dose of your medicine might be necessary.

You will have therapeutic drug monitoring blood tests if you are taking biologic medicines, such as infliximab or adalimumab, and thiopurines, such as azathioprine and 6-mercaptopurine for inflammatory bowel disease. These medicines all suppress your immune system, and are checked to ensure that they don’t make your immune system too weak.

Stool tests

Stool (poo) tests are sometimes used to monitor the effectiveness of your treatment by measuring faecal calprotectin and faecal lactoferrin levels which indicate there may be inflammation in your bowel.


Endoscopies can be used to monitor how your disease is responding to your treatment. They allow doctors to monitor inflammation in your digestive tract, and biopsies can be taken for examination under a microscope. Adults with IBD are given regular endoscopies to monitor their IBD and how it is responding to treatment, however this isn’t generally done in children unless there are changes that need to be investigated which can’t be done using other tests.

X-rays and scans

There are several types of scans and x-rays that are used to monitor your disease activity, and to check that your treatment is working effectively. These include MRI scans, CT scans, ultrasound scans, abdominal x-rays and barium enema tests. If you are being treated with medicines that can affect your bones, DEXA x-rays can be used to identify and monitor low bone mineral density.

What happens if any tests are abnormal?

If any of the tests you have to monitor your treatment indicate that it is not working effectively, or that the medicine you are taking is not suitable for you, your IBD team will contact you to discuss this. You might need to change your dosage, take additional medicines or supplements alongside your treatment, have further tests, or change to a different type of treatment.

It is really important you keep up to date with your medicine monitoring tests for your inflammatory bowel disease. If you don’t, you are at risk of your disease worsening and becoming very unwell. You are also at risk of developing serious and long-term side effects or complications. 

Your GP will also need to see relevant test results in order to continue to issue prescriptions for your medication.

Monitoring biologic medicines

When you first start biologic medicines, you will be monitored during and immediately afterwards for signs of an allergic reaction.

If you are self-injecting biologics then you will likely have your first few injections in hospital so that emergency medical help is available if you do have a reaction. Once you have had a few injections, you will no longer need to be monitored and can self-inject at home. 

Biologic infusions are always done in hospital, however the time that you will need to be monitored for afterwards will reduce as you have more infusions.

If you have a reaction, you might be given pre-medications at future infusions to reduce the risk of it happening again.

Funding to help in the production of this article was received from PredictSURE IBD, however they had no input into its content.

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