How effective is a blood test for Crohn's disease?

Blood tests may show inflammation, anaemia, infection or low levels of nutrients when Crohn's disease is active or has affected absorption. These findings are not specific: other illnesses can cause similar changes, and Crohn's disease can still be present when routine blood results are not striking.

Doctors combine the results with symptoms such as persistent diarrhoea, abdominal pain, fatigue or weight loss. Stool tests can help check inflammation and infection, while scans or a camera test of the bowel may be needed to see where inflammation is and how extensive it is.

Describe the pattern of your bowel movements, pain, bleeding, fever, appetite and weight change. Mention recent infections, travel, medicines and family history. Keep appointments for any stool test, scan or specialist review. If you already have Crohn's disease, ask whether the blood result is being used to monitor inflammation, anaemia, nutrition or a medicine's effects.

Seek prompt medical advice for persistent bloody diarrhoea, worsening abdominal pain, fever, repeated vomiting or inability to maintain fluids. Emergency care is appropriate for severe or rapidly increasing abdominal pain, a swollen abdomen, collapse, heavy rectal bleeding or marked weakness.

Ask what the blood markers suggest, whether a stool test is useful, if imaging or endoscopy is needed, and how the findings would change treatment or follow-up.