What blood tests are used to monitor IBD in children?

If your child has Crohn's disease or ulcerative colitis, blood tests are likely to become a regular part of their healthcare routine. They help the medical team monitor inflammation, check for nutritional deficiencies, assess how well treatment is working and identify possible medication side effects.

You might see lots of abbreviations on your child's results, such as CRP, ESR, FBC, haemoglobin and ferritin. Understanding what these tests measure can help you feel more confident when discussing your child's health with their gastroenterologist.

Not every child needs every test at every appointment. The tests your child has will depend on their symptoms, treatment, medical history and individual needs.

🔬 Full blood count (FBC or CBC)

A full blood count, also called a complete blood count, measures different types of cells in your child's blood. It is one of the most common tests used to monitor children with IBD.

It includes several important measurements.

Haemoglobin (Hb)

Haemoglobin is the protein in red blood cells that carries oxygen around the body.

Low haemoglobin can indicate anaemia, which may contribute to tiredness, weakness, headaches, dizziness and reduced exercise tolerance. In children with IBD, anaemia can be associated with iron deficiency, ongoing inflammation or blood loss from the bowel.

White blood cells (WBCs)

White blood cells help the body fight infections. An increased count can occur with inflammation, infection or certain medications, while a low count can sometimes indicate a medication-related problem.

Platelets

Platelets help blood clot. A higher platelet count can occur with inflammation or iron deficiency, so the result needs to be considered alongside other tests.

Red blood cell measurements

Tests such as MCV and MCH describe the size of red blood cells and how much haemoglobin they contain. They can help the healthcare team investigate different types of anaemia.

Together, these results help the team assess your child's blood health and look for changes that may need further investigation.

🔥 C-reactive protein (CRP)

CRP is a protein produced by the liver in response to inflammation. It is commonly used to help monitor inflammatory activity in children with IBD.

When inflammation increases, the CRP level may rise. If treatment is working and inflammation decreases, the level may fall.

Your child's gastroenterologist may compare CRP results over time to help assess how their disease is responding to treatment.

However, a normal CRP does not always mean IBD is under control. Some children can have active intestinal inflammation without a significant rise in CRP.

This is why CRP is interpreted alongside symptoms, other blood tests and, when appropriate, stool tests or further investigations.

🧪 Erythrocyte sedimentation rate (ESR)

ESR is another blood test used to look for inflammation in the body.

It measures how quickly red blood cells settle in a test tube over a set period. Inflammation can change the blood's properties, causing the cells to settle more quickly.

Like CRP, ESR can be raised when IBD is active. However, it is not specific to IBD and may also increase with infections and other inflammatory conditions.

ESR can change more slowly than CRP, so the two tests may provide complementary information.

Some children with active IBD have normal ESR and CRP results. The healthcare team will therefore consider the full picture rather than relying on one result.

🥚 Albumin and total protein

Albumin is a protein made by the liver. It helps maintain fluid balance in the bloodstream and carries various substances around the body.

Low albumin levels can occur in children with active IBD, particularly when inflammation is significant. Levels may also be affected by protein loss through the bowel, inadequate nutrition or certain liver and kidney conditions.

Total protein measures the combined amount of several proteins in the blood, including albumin.

These tests can help the healthcare team assess your child's nutritional status and overall health. They may also provide clues about disease activity, although low albumin does not automatically mean that IBD is flaring.

🩸 Iron studies and ferritin

Iron deficiency is common in children with IBD. It can develop because of blood loss, reduced iron intake, problems with absorption or the effects of ongoing inflammation.

Iron studies help assess your child's iron levels and iron stores. They may include:

• Ferritin: A measure of the body's stored iron.

• Serum iron: Measures the amount of iron circulating in the blood at the time of testing.

• Transferrin or total iron-binding capacity (TIBC): Helps assess how iron is transported in the bloodstream.

• Transferrin saturation: Shows the proportion of iron-binding sites occupied by iron.

Ferritin is particularly useful, but it needs careful interpretation. Because ferritin can rise during inflammation, a result within the laboratory's normal range does not always rule out iron deficiency in a child with active IBD.

The healthcare team considers the iron results alongside haemoglobin, other blood count measurements, inflammation markers and your child's symptoms.

Treating iron deficiency can help improve energy levels and support growth and development. Depending on the severity of the deficiency and how well your child tolerates oral iron, the team may recommend dietary changes, oral supplements or an iron infusion.

🌞 Vitamin D, vitamin B12 and folate

Children with IBD may be at risk of nutritional deficiencies, particularly if they have restricted diets, reduced food intake, ongoing inflammation or problems absorbing nutrients.

Vitamin D

Vitamin D helps the body absorb calcium and supports healthy bone development. It may be checked periodically, especially in children with risk factors for deficiency or concerns about bone health.

Vitamin B12

Vitamin B12 is important for red blood cell production, nerve function and growth. Children with Crohn's disease affecting the end of the small intestine, or those who have had certain intestinal surgeries, may be at increased risk of deficiency.

Folate

Folate is needed for DNA production and the formation of healthy blood cells. Low levels can contribute to anaemia.

Not every child will need all three tests at every visit. Your child's gastroenterologist or dietitian can recommend which nutritional markers should be monitored based on their individual circumstances.

🧂 Electrolytes and kidney function

Blood tests may also measure electrolytes and substances that help assess kidney function.

These can include sodium, potassium, chloride, bicarbonate, urea and creatinine.

Electrolytes help regulate fluid balance, nerve function and muscle activity. Children who have frequent diarrhoea or vomiting can lose fluid and electrolytes, making these tests particularly useful during a flare or an episode of illness.

Creatinine and other kidney-related measurements help the team assess how well the kidneys are functioning.

Kidney monitoring can also be important for children taking certain IBD medications. For example, mesalazine (also called mesalamine or 5-ASA, and sold under various brand names) can rarely affect kidney function.

The timing of these tests depends on your child's medication, medical history and treatment plan.

🧫 Liver function tests

Liver blood tests may include measurements such as ALT, AST, GGT, alkaline phosphatase and bilirubin.

These tests help assess liver health and can identify changes that may need further investigation.

Liver test abnormalities can occur for several reasons, including medication effects, inflammation or liver and bile duct conditions that sometimes occur alongside IBD.

For children taking medicines such as azathioprine or methotrexate, regular monitoring may be needed to check for possible liver-related side effects.

An abnormal result does not automatically mean that a medication is causing harm. The healthcare team will consider which tests are affected, how high the results are, whether they have changed over time and whether your child has symptoms.

💊 Blood tests to monitor IBD medication

Some medications used to treat IBD require specific blood tests to check for side effects or help guide treatment.

Azathioprine and mercaptopurine

These medicines can affect bone marrow function and liver health. Monitoring may include a full blood count and liver function tests.

In some circumstances, the team may also check thiopurine metabolites. These measurements can help assess how your child processes the medication and whether the dose may need reviewing.

Methotrexate

Children taking methotrexate generally need monitoring that includes blood counts and liver function, with other tests as recommended by their healthcare team.

Biologic medicines

Some children receiving biologic treatments may have drug levels and antibodies measured. These tests can help the team understand whether enough medicine is present in the bloodstream and whether antibodies may be affecting the treatment.

The exact tests depend on the medicine and the clinical situation.

Blood monitoring is an important part of using these treatments safely. Your child's team will explain which tests are required and how often they should be performed.

📊 How often will my child need blood tests?

There is no single schedule that applies to every child with IBD.

Testing may be more frequent when your child is first diagnosed, starts a new medication, changes their treatment or experiences worsening symptoms.

Once their condition is stable, some tests may be performed less frequently, although medication-specific monitoring still needs to continue.

Your child's gastroenterologist will decide the appropriate schedule based on their treatment and individual risk factors.

If your child takes an immunosuppressant or biologic medicine, do not assume that blood tests can be delayed simply because they are feeling well.

📉 What if my child's blood tests are normal but they still have symptoms?

This is an important question.

Blood tests provide useful information, but they cannot show everything that is happening inside the bowel.

Some children have active intestinal inflammation despite normal CRP, ESR or other routine blood results. A child may also have symptoms for reasons other than active IBD, including infection or medication-related problems.

If your child continues to experience diarrhoea, abdominal pain, bleeding, fatigue or other concerning symptoms, tell their healthcare team even if their recent blood tests were normal.

Depending on the situation, the team may recommend a stool test for faecal calprotectin, tests for infection, imaging or an endoscopic assessment.

Faecal calprotectin is measured in a stool sample rather than a blood sample. It helps assess inflammation in the intestines and can provide additional information when interpreted alongside symptoms and blood results.

📄 What if a result is outside the normal range?

Seeing a result marked as high or low can be worrying, especially when it relates to your child.

However, one abnormal result does not automatically mean their IBD is worsening or that their treatment needs to change.

Results can be affected by many factors, including infections, recent illnesses, hydration, nutritional deficiencies and medication.

The healthcare team will consider the result alongside previous tests, your child's symptoms, their medications and the laboratory's reference range.

If you are unsure about a result, ask the IBD team to explain:

• What the test measures.

• Whether the result is significantly abnormal.

• Whether it has changed compared with previous tests.

• Whether further testing or treatment is needed.

• When the test should be repeated.

If your child is becoming more unwell, do not wait for the blood results to be reviewed before seeking medical advice.

📝 How parents can prepare for blood tests and appointments

A few simple steps can help you keep track of your child's results and make appointments more useful.

• Keep a record of results: Save copies of blood tests or use a health record app to track changes over time.

• Write down questions: Note any results you do not understand before the appointment.

• Record symptoms: Let the team know about changes in bowel movements, pain, energy, appetite or weight.

• Keep medication details up to date: Include medication names, doses and any recent changes.

• Ask about follow-up: Check whether additional tests are needed and when you should expect results.

• Understand the contact plan: Find out who to contact if a result is abnormal or your child's symptoms worsen.

You do not need to interpret every result yourself. Your child's healthcare team can explain what the results mean in the context of their care.

💛 The takeaway

Blood tests are an important part of monitoring Crohn's disease and ulcerative colitis in children. They help the healthcare team assess inflammation, identify anaemia and nutritional deficiencies, monitor organ function and check for possible medication side effects.

However, blood tests are only one part of your child's care. Symptoms, growth, stool tests and other investigations may also be needed to understand how well their IBD is controlled.

If you have questions about your child's results, ask their gastroenterologist or IBD nurse to explain them. Understanding what is being monitored can help you feel more informed and confident as you support your child.