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An introduction to blood tests commonly measured in children with IBD

Professor Andrew Day —

This aims to outline the key features of blood tests commonly used in children with IBD. It does not cover every test, or every situation.

Erythrocyte Sedimentation Rate (ESR)

The ESR is a measure of the “stickiness” of red blood cells: how quickly the red blood cells settle in a column. Inflammation leads to an increased ESR: but this doesn’t indicate where the inflammation is coming from. ESR changes tend to occur slowly (for example, after treatment of flare of IBD, the ESR may return to normal levels after symptoms have improved and after some of the other tests)

Normal ESR is less than 10

C-Reactive Protein (CRP)

CRP is a protein made in the liver. Increased production is triggered by several proteins involved in inflammation. CRP increases with inflammation of any source. Changes in CRP tend to occur quickly: CRP may increase early in a flare and typically falls quickly with treatment of a flare.

Normal CRP less than 3 (in most labs)


Platelets are one of the types of blood cells made in the bone marrow. Platelets have many functions, including helping with the formation of clots.

A high platelet count can occur with inflammation, but is not specific to gut inflammation.

Normal range is typically 150-400


Albumin is a protein made in the liver. Albumin has many functions in the body, such as carrying other compounds around the body.

Low levels of albumin can occur when the gut is more inflamed (with albumin being lost in the stool). Low albumin can also reflect impaired liver function, losses of albumin from other sources (such as through the kidneys) or significant malnutrition (especially inadequate protein intake in the diet).

Albumin levels take a while to recover.

When albumin is low in the context of active inflammation, improving the inflammation is the only way to improve the levels (eating excessive amounts of protein doesn’t help)

Typical normal range is 37-45 grams/litre

Blood count

A full blood count includes measurement of three key elements made in the bone marrow: red blood cells, white blood cells and platelets.

Processes that affect the bone marrow can lead to low levels of these three cell lines

Red blood cells incorporate the haemoglobin (which carries oxygen). Low levels (anaemia) can reflect inadequate amounts of key components (such as low iron levels) or can reflect loss of blood (e.g. bleeding from the gut).

White blood cells are important for responding to infection or inflammation

Platelets have many functions, including formation of clots.

Liver chemistry

A number of different tests can inform us about processes affecting the liver.

Bilirubin is a break-down product of red blood cells. The liver cell process bilirubin so that it can be eliminated in bile. Increased bilirubin levels can occur when something affects the liver cells or affects movement of bile flow through or out of the liver. When the bilirubin increases to a certain point this can be recognised by a yellow hue to the white of the eyes or of the skin.

GGT is a protein that can increase when the bile ducts inside or outside the liver are irritated or damaged.

AST and ALT are two proteins that can be released from liver cells when they are damaged or irritated. Examples are liver infections or damage from drugs

There are two main types of IBD-associated liver disease: sclerosing cholangitis and autoimmune hepatitis (many children with IBD-associated liver disease can have liver disease with features of both). Sclerosing cholangitis typically leads to increased levels of GGT, while autoimmune hepatitis (affecting the liver cells) typically leads to increased levels of AST and ALT.

Albumin (as above) is produced in the liver. Severe processes affecting the liver can interfere with the production of albumin and lead to lower levels in the blood stream.

Tests used for azathioprine and 6-mercaptopurine

Azathioprine and 6-mercaptopurine are both called thiopurines. These drugs are broken down by a series of enzymes in the liver leading to various breakdown products. The key enzyme can be measured as can several breakdown products.

TPMT is one of the key enzymes that breaks down these drugs. Most people have good activity of the enzyme, but a small number of people have reduced levels and a very small number of people have very reduced activity. Reduced function of the enzyme can mean that the drugs are broken down much more slowly, with potentially greater side-effects.

TPMT enzyme activity can be measured on a blood test. The gene responsible for the how this enzyme functions can also be assessed on the same blood test

6TGN and 6MMP are two of the key breakdown products of the thiopurines. Low 6TGN levels indicate that the person is not having enough of the drug. Levels that are too high, however, can lead to interruption of the bone marrow (leading to low levels of the blood cells). On the other hand, very high levels of 6MMP can be associated with irritation of liver cells. These two breakdown products (metabolites) can be measured at intervals to ensure that the dose of the drug is just right for the person and to help avoid side-effects of the drug.


Low levels of several micronutrients and vitamins can occur in IBD. Measurement of these can help to detect low levels (deficiencies) and also to show improvement after giving extra amounts (supplements)


Ferritin can indicate stores of iron in the body (but this protein also increases when there is inflammation present). Other markers of iron status include the level of iron.

Typically, when someone is iron deficient the iron levels and ferritin levels will be reduced. In time, this will then lead to reduced production of haemoglobin and on to iron-deficient anaemia.

Vitamin D

This vitamin is often low in people with IBD. Vitamin D can be absorbed from the gut, but the main source is from sunshine exposure. Avoidance of sunshine or dark skin pigmentation can lead on to vitamin D deficiency. Vitamin D has a number of jobs: one of these is increasing absorption of calcium from the gut. Deficiency of vitamin D can therefore lead on to reduced bone health (and increased risk of fractures). Vitamin D also has roles in immune responses.

Vitamin B12

Vitamin B12 is absorbed in the last section of the small bowel. Vitamin B12 is found in meat in high quantities. Low B12 levels can be seen after the end part of the small bowel has been removed (surgery), or in people who do not include meat in their diet.