Blood Tests

Blood tests (also referred to as histology) are used by health care providers (HCPs) to help rule out other potential causes of symptoms, and to decide what other testing is needed to make a diagnosis of inflammatory bowel disease (IBD). There are several different types of tests that are typically used when checking for IBD activity, signs of infection, anemia, nutritional deficiencies and/or other diseases. Below you will find more information about these different types of blood tests. 

Complete Blood Count (CBC)

The complete blood count (CBC) is commonly used by HCPs when testing for Crohn’s and colitis. It collects information about the types and numbers of cells in the blood. A CBC is typically done by a nurse or lab technician in the clinic or hospital.

Blood is drawn by inserting a needle into the vein of an arm. The blood is then sent to the lab for analysis of the cells and plasma. Sometimes it can take up to a week for the lab to send the results to your provider. A CBC normally includes: 

Red blood cells (RBCs) and Hemoglobin

Human blood is primarily made up of RBCs, which are produced in bone marrow. They help to supply tissues in the body with oxygen and nutrients. Hemoglobin is a protein found in RBCs that is needed for to carry oxygen from the lungs to the rest of the body and return carbon dioxide from the body back to the lungs to be removed by exhalation. 

Low levels of RBCs and/or hemoglobin may be a sign of abnormal blood loss or internal bleeding, anemia, malnutrition and/or other diseases.

With IBD, the lining of the large intestine becomes inflamed which causes ulcers and bleeding to occur in the colon or rectum. Inflammation in the intestine can also reduce the absorption of iron and other vitamins (malabsorption). 

White blood cells (WBCs)

WBCs (also called leukocytes) are made in the bone marrow and account for 1% of human blood. There are 5 types of WBCs including neutrophils, lymphocytes, monocytes, eosinophils, and basophils. These cells play an important part in the body’s immune system because they produce and/or carry antibodies to the rest of the body to help fight bacterial and viral infections, and other foreign materials.

High levels of WBCs may be a sign of infection and/or inflammation that is occurring somewhere in the body. 

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Nutritional status

Blood tests are also used to check plasma levels of iron, ferratin, vitamin B12 and folic acid. These are important biomarkers, which are indicators from biological substances that can be measured. These biomarkers look for signs of malnutrition, anemia, and/or chronic disease.

In people diagnosed with IBD, inflammation in the lining of the intestine can interfere with the body’s ability to absorb nutrients from food and drink. If you've had surgery of the gastrointestinal tract (removal of parts of the small intestine) there is a high risk for malabsorption and/or malnutrition. Health care providers also use biomarkers of malnutrition to help determine disease activity (gut inflammation) and severity. 


Iron is a mineral in the blood that is needed for the protein, hemoglobin, in red blood cells (RBC). It is also used by other proteins such as transferrin in blood or ferritin in bone marrow and tissues in the body. Iron deficiency may be a result of abnormal bleeding in the gastrointestinal tract, from stomach ulcers and/or severe inflammation. 

Low levels of iron can cause fatigue or weakness, hair loss or thinning, and anemia. If you have IBD, anemia is an important factor when HCPs test for disease activity. 


Ferritin is a protein in the body that binds to iron. Ferritin levels in the blood are used to measure the amount of iron stored in the body. It is also used to test for anemia, which may be caused by iron deficiency, chronic disease, and/or abnormal bleeding. 

Low-levels of ferritin are usually associated with iron deficiency. High-levels of ferritin may be a sign of chronic disease. It is also possible for ferritin levels to be normal if anemia is due to multiple causes. If you have already been diagnosed with IBD, anemia is an important factor when HCPs test for IBD disease activity.

Vitamin B12

Vitamin B12 is a B complex vitamin that your body needs to make red blood cells (RBC) and have a healthy nervous system, which is made up of nerves and specialized cells (neurons) that transmit signals between different parts of the body. It includes both the Central Nervous System (CNS, brain and spinal cord) and the Peripheral Nervous System (PNS, nerves that go through the whole body).

Low levels of vitamin B12 may cause anemia and interfere with nervous system functioning. Anemia is an important factor when HCPs test for IBD disease activity.

Folic Acid

Folic acid is a type of folate that is needed to make red blood cells (RBC), white blood cells (WBC) and platelets. It is normally tested at the same time as Vitamin B12. 

Very low levels of folic acid can cause diarrhea, weakness and fatigue.

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C-Reactive Protein (CRP)

The CRP is a protein made in the liver and increases when inflammation is occurring somewhere in the body. High CRP levels may be a sign of anemia, infections and/or chronic disease. Further testing is needed to determine the cause and location of the inflammation.

If you've been diagnosed with IBD, health care providers typically test for CRP during routine appointments to check for disease activity (gut inflammation) and severity. 

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