IBD blood tests and children

Learn about why you have blood tests, what the tests can tell us, and what to do if you are feeling worried about having your test.

What is a blood test?

A blood test involves taking a sample of your blood from a vein, usually in your arm or the back of your hand. To do this a nurse will put a tiny needle into your vein, which is attached by a thin plastic tube to a syringe. The syringe will be used to draw your blood up through the tube and into a small container. 

Only a very small amount of blood is taken, and once enough has been taken, the needle will be gently removed. A piece of cotton wool will be pressed down on the place where the needle was - this will stop the flow of blood. You will then have a plaster put on to protect the area and keep it clean.

The whole blood test is over within a minute or two and shouldn’t be painful, just a bit uncomfortable. You can have special numbing cream or freeze spray put on your skin which can help to stop you feeling the needle going in.

Your blood sample will then be sent to a laboratory to be tested.

Blood tests and paediatric IBD

By the time you meet your IBD team, it is likely you will already have had blood tests done. However, at your first appointment in the paediatric gastroenterology department, an initial blood test will be carried out, which will be used to find out lots of things that will help with your diagnosis. 

Some of the reasons you may have a blood test include;

  • Diagnosis - Blood tests cannot be used to directly diagnose inflammatory bowel disease (IBD), but they can tell us if there is inflammation in your body, and that further investigations need to be done
  • Monitoring the activity of inflammation in your body - When you have a flare up, there will be more inflammatory markers in your blood. Testing your blood for inflammatory markers will give your IBD team warning that your disease is active
  • Screening tests - It is important to check for infectious diseases (such as tuberculosis or chicken pox) before you start taking medicines that suppress your immune system. You can also check in advance that your body will be able to tolerate some medicines
  • Checking levels of medicines in your body - Drug monitoring is used to ensure you have the right level of medicine in your body, not too little or too much. This will mean the medicines will work as effectively as possible
  • Monitoring how your body is tolerating medicines - Some medicines can affect other parts of your body, for example your kidneys, liver and bones. Blood tests can be used to make sure your body is functioning properly while on these medicines
  • Checking for anaemia - Lots of people with IBD can develop iron deficiency anaemia, where your red blood cells and iron levels are too low, causing symptoms such as tiredness and lack of energy. Blood tests can be used to measure your red blood cells and your iron levels
  • Checking vitamin and mineral levels - People with IBD can often be deficient in (not have enough) certain vitamins and minerals which are essential to keep you well

You can have blood tests at your clinic appointments, at your GP surgery, and sometimes, when you are starting a new type of medicine and need regular blood tests, community nurses might come to take blood tests at your home.


Common types of blood tests used in children with Crohn's disease, ulcerative colitis or IBDU include:

  • FBC (Full blood count) - A full blood count measures the amount and different types of blood cells (red cells, white cells and platelets). This can be used to check for signs of inflammation (which would show up as a higher white blood cell count and/or an increase in the number of platelets), to check for anaemia (your red blood cell count would be lowered), and to monitor the effect of medicines on your bone marrow
  • Ferritin and transferrin tests - Ferritin is a protein that can be measured to see if there is inflammation in your body. Low levels of ferritin and transferrin can also mean you have low levels of iron in your blood, which could mean you have anaemia
  • U&E (Urea and electrolytes) - If you have diarrhoea, it could mean you get dehydrated. Measuring your electrolytes (which are important to ensure your body works properly) will help to monitor this. A U&E test can also be used to make sure your liver and kidneys are functioning properly whilst taking certain medicines, and can check for rare liver complications that can affect some people with IBD
  • CRP (C-reactive protein) and ESR (Erythrocyte sedimentation rate) - These are both inflammatory marker tests; measuring these biomarkers in your blood can help to see if there is inflammation in your body
  • TPMT (Thiopurine s-methyltransferase) - This test checks to see if you are at increased risk of having side effects if you take thiopurine medicines, such as azathioprine or 6-mercaptopurine
  • Tests for vitamins and minerals - This will include levels of vitamin B12 and folic acid which can be affected if you have damage or inflammation in your small intestine. Your levels of calcium and phosphate can also be affected by inflammation in your small bowel, and/or by a restricted diet, and by some medicines. Vitamin D levels can be low if you have Crohn’s disease, and your magnesium levels can be low if you are being sick a lot or have diarrhoea

Your IBD team will explain to you what they are looking for in your blood. This may feel overwhelming and you may want to write the information down so you can read about it another time.

What happens if I’m scared of blood tests?

It is normal to feel a little worried or anxious about having a blood test, but some people can become very scared, or even develop a phobia (an intense, irrational fear) of blood tests.

  • If you are feeling worried, tell your IBD nurse or the nurse who is doing your blood test
  • Remember these nurses are very experienced and will try to help you feel calmer and more comfortable 
  • You may be asked if you would like to see a play specialist. They can help to keep you busy and take your mind off your test by reading and playing games with you
  • If you are feeling extremely worried, and it is making blood tests difficult, your IBD team can ask the clinical psychology team to help you work to overcome your fears


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