Inflammatory bowel disease (IBD): How to read your blood tests?

Published May 13, 2019 • Updated May 20, 2019 • By Andrea Barcia

When you have inflammatory bowel disease, blood tests can be frequent. But do you know the values to be monitored for these blood tests? Do you know what additional tests may be required? Read our guide for patients with ulcerative colitis or Crohn's disease.

Inflammatory bowel disease (IBD): How to read your blood tests?

The values presented in this article are reference values. However, they may vary according to the individual. Refer to your doctor's instructions.

What are IBDs? What are they?

Chronic inflammatory bowel diseases, commonly known as IBD, include Crohn's disease and ulcerative colitis. Both of these diseases are characterised by abnormal inflammation of the intestinal wall. This pathological similarity explains why the follow-up of Crohn's disease (analysis of biological and endoscopic data) is very similar to that of ulcerative colitis.

Monitoring by analysis of biological data

Prevent possible anemia

Why this test?

Chronic inflammation of the intestinal wall results in poor absorption of minerals and other vitamins. It is therefore essential to monitor blood levels of iron, vitamin B9 (folic acid) and vitamin B12 (cobolamine) once or twice a year.

The usual values

Serum iron in men
70 - 145 µg/dL

Serum iron in women
50-150 µg/dL

Vitamin B9
5 -15 µg/L

Vitamin B12
130-180 ng/L


A deficiency in one or more of these parameters can result in a defect in the synthesis of red blood cells (otherwise known as anemia) leading to poor oxygenation of the organs.

Monitor the effects of treatments

Why this test?

The second element of biological monitoring in the monitoring of IBDs is the non-toxicity and proper assimilation of the treatment(s) put in place. Despite the verification of compatibility between patient and Azathioprine (AZASAN®, IMURAN®) therapy, monitoring of patient tolerance remains essential. Thus, a regular check of the blood count and a platelet assay are performed to rule out any risk of leukopenia (white blood cell deficiency resulting in a deficiency of the immune system).

Common values

Male CBCs
4.2-5.7 Millions/µL

Female CBCs
4.0-5.3 Millions/µL (female)


Liver function and renal function

It is also important to check the proper hepatorenal function which can be damaged by the different treatments (Methotrexate (OTREXUP®, RASUVO®, TREXALL®, XATMEP®), Mesalamine (ASACOL HD®, APRISO®, CANASA®, DELZICOL®, LIALDA®, PENTASA®, ROWASA®)). We will therefore look at the determination of ALAT and Gamma-GT in the blood for liver function and creatinine for kidney function.

Why these tests?

ALAT and Gamma-GT values are used to assess the state of the liver; the higher their values, the more advanced the liver damage is. The same applies to creatinineemia with regard to renal function. The higher the creatinine value, the lower the kidney performance.

Common values

ALAT in men
8-35 IU/L

ALAT in women
6-25 IU/L

Gamma-GT in men
>45 IU/L

Gamma-GT in women
>35 IU/L

Creatininemia in men
6-12 mg/L

Creatinine levels in women
4-10 mg/L

Biological examinations related to corticosteroid therapy

Why these tests?

The introduction of corticosteroid therapy (corticosteroid treatment) requires monitoring different biological parameters. Thus, a fasting blood glucose test is performed one week after the start of treatment (this is essential in the case of diabetes). Bone density monitoring is also performed if the treatment is spread over more than 3 months. Finally, an ophthalmic examination is considered when the corticosteroid therapy exceeds the cumulative 6 months.

Common values

Fasting blood glucose
0.63 - 1.1 g/L (i.e. 3.5 - 6.1 mmol/L)

Bone densitometry with a T-score

< -1

What are the markers of inflammation (CRP, VS)?

When the body detects substances that seem foreign to it, it sets up a defense strategy to recognize, destroy and eliminate them: this is the inflammatory reaction. The causes of inflammation are multiple: they can be of external origin (bacteria, viruses, skin lesions, blows...) or internal (autoimmune diseases such as IBD, cancers...)

 C-Reactive Protein (CRP) is an inflammatory protein, synthesized by the liver, which increases its blood concentration within a few hours in the event of inflammation. CRP plays an important role in mobilizing and activating the immune defences (white blood cells) and stimulating the destruction process of cells considered as foreign (phagocytosis). The higher the CRP value, the more important the inflammatory response.

Follow-up by endoscopic examinations

Why these tests?

Additional examinations using endoscopic methods (colonoscopy, ileo-colonoscopy, etc.) may be necessary to confirm a diagnosis or to assess the intensity and severity of an attack.

In case of suspicion of precancerous dysplasia, a chromo-endoscopy (colonoscopy with mucosal staining) accompanied by biopsies is performed for analysis and detection of possible lesions.

The usual values are to be qualified. First of all, talk to your doctor about it!

If you have already looked at a blood test report, you have seen that next to the result there are "usual values" or "reference values", with a lower and an upper limit. To define these reference values, biologists sample data from healthy persons. However, as in any statistical analysis, 5% of the sample is outside the norm. Therefore, being slightly outside the "reference values" does not always mean that there is a disease. Thus, in the face of an analysis that seems "abnormal", there is no need to worry without discussing it with the physician who prescribed the blood tests.


avatar Andrea Barcia

Author: Andrea Barcia, Health Writer

Andrea specialises in managing online patient communities and writing health articles. She has a particular interest in the fields of neuropsychology, nutrition and sport.

Andrea holds a master's degree in... >> Learn more

Who reviewed it: Alizé Vives, Pharmacist, Data Scientist

Alizé holds a PharmD and a master's degree in strategy and international business from ESSEC Business School in France. She has several years of experience working with patients and members, conducting surveys for... >> Learn more


on 5/22/19

Excellent article, especially for those not too familiar with the value of the blood tests. I learned some things here also. Thank you.

on 2/26/21

Yes, excellent article. What about the fecal calprotectin level?  I thought that was an important level to watch as well.

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