IBD Basics: Blood Tests

Disclaimer: This information is based on my own research into this particular aspect of IBD as well as some personal experience and should not be used as medical advice or a diagnostic tool. The suggestions given within are taken from sources laid out in the references header.  If you seek advice regarding the things you experience within your own disease, please contact your IBD team for medical advice.

If you are looking for the entire ‘IBD Basics’ series, you can find them all here.

What are blood tests & Why are they important?

Blood tests are one of the most common medical tests for diagnosing any condition. Blood tests are used to both help with a diagnosis of IBD and also to monitor your condition once you have a diagnosis. However, here are no blood tests that can directly diagnose IBD. Blood tests are one tool in a Gastroenterologist’s tool box to help determine your condition, as well as determine when and if it is in remission or flaring up.

A blood test can be done to test for inflammation in the body. This test does not show where in the body the inflammation is occurring but it does indicate that further tests as to the source of the inflammation need to be done.

Why are they used to treat IBD?

Blood tests are routinely used to assess your condition and your medications effectiveness. As IBD is a fluctuating, ongoing condition, it is likely that you will need to have some of these tests repeated from time to time. After your initial diagnosis, further tests – CT scans, MRI scans, endoscopy – may be needed to determine which treatments are most suitable for you, how well you are responding and whether your disease is in remission.

How are they used to treat IBD?

Drawing blood for laboratory testing is usually a relatively simple and quick procedure. A phlebotomist will typically draw a small amount of blood from a vein in your arm, which is then sent to a laboratory for analysis. Blood may be drawn in your hospital’s blood clinic, or at an off site collection centre; such as your GP surgery or an Urgent Care Centre. This depends on which NHS Trust your hospital is under and their procedures. Results are usually available a couple of days after, but this is dependent on the type of blood testing required.

Routine blood will look at four things: Inflammation and infection, anaemia, dehydration and low albumin or protein. These tests are done with the following:

  • FULL BLOOD COUNT (FBC) – this will look at levels of white blood cells, red blood cells and platelets. These will give an indication to your general health and some clues as to some particular health conditions. WBC will be raised if there is an infection or inflammation but will also be raised if on immunosuppressants such as Azathioprine. Platelets are the body’s natural clotting factor and could be raised in times of inflammation. RBC show how well oxygen is flowing around the body. If this is low, it could indicate anaemia – where there is too little haemoglobin and/or too few red blood cells.
  • C-REACTIVE PROTEIN (CRP) & ERYTHROCYTE SEDIMENTATION RATE (ESR) – Inflammation can raise certain proteins in the blood, assessed by these two specific tests. CRP generally rises first and falls first too, whilst ESR remains raised for longer, which is helpful to assess how well a primary treatment such as steroids is working. While levels can be used to monitor response to treatment, these proteins are not specific to the gut and may also increase when there is inflammation elsewhere in the body. Also, a normal level of CRP does not necessarily rule out inflammation. This is why a stool sample – Fecal Calprotectin – is considered the best way to determined gut based inflammation as it is much more sensitive.
  • LIVER FUNCTION TEST (LFT) INCLUDING ALT – LFTs are a measure of how well your liver is working. An LFT will test the levels of enzymes  –  proteins speeding up chemical reactions in the body – that are made in the liver and can leak into the blood when the liver is damaged. An LFT will also measure the levels of albumin – a protein made by the liver which maintains the correct fluid pressure in the blood. Production of albumin is reduced in some liver disorders. Abnormal levels of both enzymes and albumin can indicate liver problems.
    The liver can also be affected by medications used to treat IBD so screening is also done for liver complications. It is also used to help diagnose rare liver complications of IBD such as Primary Sclerosing Cholangitis (PSC) – a condition in which the ducts carrying the digestive juice bile from the liver to the gut become inflamed.
  • FERRITIN AND TRANFERRIN LEVELS – blood levels of ferritin – and less frequently transferrin – are measured, along side a FBC to diagnose iron deficiency anaemia. Ferritin is the protein that binds to iron to store it in cells. Transferrin is the protein that transports iron around the body – carrying it away from the gut for storage and to the bone marrow to make red blood cells. Blood levels of ferritin and transferrin reflect the total amount of iron stored in the body and are used to distinguish iron deficiency anaemia from other causes of anaemia (such as chronic disease).
  • UREA AND ELECTROLYTES (U&E) – IBD patients with acute diarrhea will often suffer with dehydration. A U&E test will measure the levels of: Electrolytes (dissolved salts such as sodium, potassium, chloride and bicarbonate), Urea (formed from the breakdown of protein from food), and Creatinine (formed from the breakdown of muscle). It will also measure how well your kidneys are functioning.


  • THIOPURINE S-METHYLTRANSFERASE TEST (TPMT) – The level in the blood of the enzyme TPMT should be assessed before starting treatment with the drugs Azathioprine or Mercaptopurine. TPMT breaks down these drugs, with the result that people with lower levels of the enzyme are more likely to experience side effects, and should start on a lower dose. Unfortunately, this test is not effective at identifying everyone who may get side effects.
    • VITAMIN B12 & FOLIC ACID: B12 is absorbed in the small bowel and levels can be affected if there is damage or inflammation in that area. Also, if you have had surgery, levels would also be affected and supplements would be needed. Folic acid is also absorbed here and is also affected by taking medication such as Methotrexate and Sulphasalazine. These two work together to form healthy blood cells.
    • VITAMIN D: The body requires Vitamin D to absorb calcium from the diet, with the result that people who do not have enough vitamin D can suffer from osteomalacia (softening of the bones). Vitamin D is also probably important in maintaining a healthy immune system. Blood tests are used to check for low levels of vitamin D, and to monitor the dose of vitamin D supplement needed. Levels of vitamin D are often low in people with IBD due to reduced intake through diet and reduced absorption due to inflammation or surgery.
    • MAGNESIUM: is important for healthy bones and also muscles. People who suffer from severe diarrhoea and/or vomiting can end up with low magnesium levels.
    • CALCIUM & PHOSPHATE: These are both important for bone health. They are absorbed in the small intestine, so some IBD patients can have problems with absorbing them. People may also suffer from low levels due to having a restricted diet.
  • ANITBODIES – Whilst having biologic therapies for your IBD, you might develop an immune response against these drugs which leads to them becoming less effective. Some hospitals do offer regular blood tests to check drug levels, and if the levels are found to be low, they test whether antibodies – the proteins that identify foreign invaders – have formed against these drugs. If antibodies are found, doses can be increased or treatments changed. These therapies include:
    • Infliximab – Remicade or bio-simliar Inflectra or Remsima
    • Adalimumab – Humira
    • Vedolizumab – Entyvio

Screening tests:

  • HEPATITIS B OR C, TUBERCULOSIS (TB), HIV OR CHICKEN POX – Before starting any immunosuppressant drug for your IBD, screening of these particular conditions is very important. Because of how immunosuppressants work – they reduce the effectiveness of the immune system – knowing if you have any of the above, or have not been vaccinated for TB or chicken pox, can impact on how well your body can find off infection; hopefully preventing you becoming seriously unwell from an infection whilst taking an immunosuppressant.  If you are found to have one of these infections, it will need to be treated before starting treatment.


Side Effects & Important Information

  1. Side Effects:
    • A blood test may make you feel faint. If you feel unwell during the test let person taking your blood know. Also let them know if you are afraid of needles or have a history of feeling unwell during blood tests.
    • You may experience a bruise and slight pain around the area where the test was done for a few days afterwards.
    • There may be a small amount of bleeding from the site of the test for a short time.
  2. Estimates suggest, at any one time, anaemia affects one in four people with Crohn’s and one in five with UC. Anaemia, which can make you feel tired and short of breath, can be caused by bleeding in the intestines, poor absorption of iron and restricted food intake. It is recommended that people with active IBD should be regularly screened for anaemia.
  3. Some of the drugs used in IBD, such as Azathioprine and Mercaptopurine, can affect the bone marrow (where the body manufactures blood cells) and reduce levels of red cells, white cells and platelets. People taking these drugs should have regular FBC tests.
  4. Regular U&E tests are often recommended for people on IBD drugs, especially Mesalazine.
  5. It is important to get your blood tested when recommended by your IBD team .Bloods are a good first indicator for something being to show as the blood reacts first to infections. For several medications for IBD, they require regular blood tests to track the effectiveness of the medication but also the start of any serious side effects. So it is best practice to keep on top of your blood tests.

Typical & Healthy Ranges for Blood Tests Common in IBD – in order as presented above.

WBC (white blood cell) leukocyte count: 4,300 to 10,800 cmm
White blood cells help fight infections, so a high white blood cell count could be helpful for identifying infections. It may also indicate leukemia, which can cause an increase in the number of white blood cells. On the other hand, too few white blood cells could be caused by certain medications or health disorders.

WBC (white blood cell) differential count: Neutrophils – 40% to 60% of the total. Lymphocytes – 20% to 40%. Monocytes – 2% to 8%. Eosinphils – 1% to 4%. Basophils – 0.5% to 1%

This test measures the numbers, shapes, and sizes of various types of white blood cells listed above. The WBC differential count also shows if the numbers of different cells are in proper proportion to each other. Irregularities in this test could signal an infection, inflammation, autoimmune disorders, anemia, or other health concerns.

RBC (red blood cell) erythrocyte count: 4.2 to 5.9 million cmm
We have millions of red blood cells in our bodies, and this test measures the number of RBCs in a specific amount of blood. It helps us determine the total number of RBCs and gives us an idea of their lifespan, but it does not indicate where problems originate. So if there are irregularities, other tests will be required.

Platelet count : 150,000 to 400,000 mL
Platelets are small portions of cells involved in blood clotting. Too many or too few platelets can affect clotting in different ways. The number of platelets may also indicate a health condition.


CRP: < 5 mg/L

ESR: < 20 mm/hr.


ALT (alanine aminotransferase): 8 to 37 IU/L
This test looks at levels of the liver enzyme ALT. When all’s well with your liver, your score on this test should be within range. Anything higher may indicate liver damage.

Albumin: 3.9 to 5.0 g/dL
A protein made by the liver, albumin levels can be an indicator of liver or kidney problems


Iron:  5.8 – 34.5 μmol/L

Transferrin: 2.0-3.60g/L

Hematocrit (Hct): 45% to 52% for men; 37% to 48% for women
Useful for diagnosing anemia, this test determines how much of the total blood volume in the body consists of red blood cells.

Hemoglobin (Hgb): 13 to 18 g/dL for men; 12 to 16 g/dL for women
Red blood cells contain hemoglobin, which makes blood bright red. More importantly, hemoglobin delivers oxygen from the lungs to the entire body; then it returns to the lungs with carbon dioxide, which we exhale. Healthy hemoglobin levels vary by gender. Low levels of hemoglobin may indicate anemia.


Urea: 2.5 – 7.8 mmol/L

Creatinine: 0.5 to 1.1 mg/dL for women; 0.6 to 1.2 mg/dL for men (the elderly may be slightly lower)
The kidneys process this waste product, so elevations could indicate a problem with kidney function.

Potassium: 3.7 to 5.2 mEq/L
This mineral is essential for relaying nerve impulses, maintaining proper muscle functions, and regulating heartbeats. Diuretics, drugs that are often taken for high blood pressure, can cause low levels of potassium.

Sodium: 135 to 145 mEq/L
Another member of the electrolyte family, the mineral sodium helps your body balance water levels and helps with nerve impulses and muscle contractions. Irregularities in sodium levels may indicate dehydration; disorders of the adrenal glands; excessive intake of salt, corticosteroids, or pain-relieving medications; or problems with the liver or kidneys.


Vitamin B12: 180-914 ng/L

Folic Acid: 2-20 ng/mL

Vitamin D:  30 to 74 ng/mL

Magneium: 0.7 – 1.0 mmol/L

Calcium: 9.0 to 10.5 mg/dL (the elderly typically score a bit lower)
Too much calcium in the bloodstream could indicate kidney problems; overly active thyroid or parathyroid glands; certain types of cancer, including lymphoma; problems with the pancreas; or a deficiency of vitamin D.

Phosphate: 0.8 – 1.5 mmol/L

TMPT: Deficient – <10mU/L. Low – 20-85mU/L. Normal – 86-185mU/L. High – >185mU/L.



More sophisticated blood tests are now being used to help distinguish between Crohn’s disease and ulcerative colitis. The newer tests look at proteins called antibodies, which are produced by the immune system. There are two antibodies of long-standing interest:

  • Perinuclear anti-neutrophil antibodies (pANCA)
  • Anti-Saccharomyces Cerevisiae antibody (ASCA)

These antibodies are considered biomarkers, defined as measurable substances in the body that indicate the presence of disease. Many patients with Ulcerative Colitis have the pANCA antibody in their blood; patients with Crohn’s Disease are more likely to have ASCA in their blood. However, these antibody tests are not foolproof. In some cases, patients have neither antibody, while others who carry one type may actually have the opposite or neither disease.

Researchers are investigating other possible biomarkers that could be used to easily and inexpensively screen for Crohn’s Disease or Ulcerative Colitis and their complications. For example:

  • A protein called calprotectin, measured in the stool, may predict relapse.  High levels of C-reactive protein (CRP) have been shown to predict patients’ response to biologic therapies (e.g., Infliximab or Adalimumab).
  • Anti-flagellin antibody (CBir1) may be a marker of Crohn’s Disease complicated by fistulas, perforations, or other serious problems.

Some of these markers are clinically available, and doctors are using them to measure disease activity and response to treatment. However, none of them are without shortcomings. Further use of them is needed to examine how effective they can be in patients.

My Experience

Having had IBD for seven years now, I have had my fair share of blood tests over the years. I’ve been tested for all of the typical bloods mentioned above, as well as more specialist ones for my GYN and my Heptologist over the last couple of years. Whilst blood tests are always pleasant, I have gotten used to them somewhat. Blood taken in a outpaitent setting – i.e when I’m not admitted to hospital – has become easier over the years because I have become able to tell which veins are good for getting a decent amount of blood from. I’ve also learnt to get as hydrated as possible so that my veins do not fall or move whilst trying to poke me.

This is a different story whilst in hospital trying to get routine bloods when dehydrated or trying to get cannulas placed for infusions or fluids. But for these, I usually let them poke me several times as I know how important it is to get the cannula in. And whilst they hurt and have sometimes blown within minutes, I’ve just taken it to be part and parcel of my condition. Routine bloods for me happen every eight weeks, sometimes more if I have more appointments with my specialists outside of Gastroenterology.

How have you found your experience with blood tests for IBD? Any bad experiences? Do you have routine bloods drawn to keep everything in check or is it when a problem occurs?

Do you have any questions or queries? Or just want to share your own experiences? Leave me a reply or tweet me @sapphire20 or find my blog page on Facebook!


Crohn’s Colitis Foundation of America:  Diagnosising Crohn’s disease and Ulcerative Colitis

Crohn’s and Colitis UK: Tests and Investigations for IBD

IBD Relief: Blood Tests for IBD

InflammatoryBowelDisease.net : Blood Tests

World Gastronterlogy Organisation (WGO) : Global Guidelines – Inflammatory Bowel Disease 

Newport Natural Health: Blood Test Results – Your Guide to Understanding the Numbers


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