A bloated feeling after eating, cramps, a restless gut. Maybe you have blamed it on stress or "the wrong food" for years, and sometimes that is true. But if stomach complaints persist for weeks or keep returning, a blood test can give surprising direction. Not every cause is visible in your blood, but a few important conditions do leave traces.
My stance: with persistent stomach complaints, blood is not the finish line but a smart first step. It rules out a handful of treatable causes before you end up in aimless self-experimentation.
When is a blood test useful for stomach complaints?
Not every bloated belly after a heavy meal is a reason for a test. But with persistent or recurring complaints, certainly with warning signs, it pays to look further. Think of:
- A bloated feeling daily or almost daily
- Stomach pain that does not improve with dietary changes
- Changing bowel habits, alternating diarrhoea and constipation
- Unexplained weight loss
- Fatigue combined with gut complaints
- Blood or mucus in the stool
Which blood values are useful for stomach complaints?
The table below is your decision aid: per value you see what it can detect and what an abnormal result can mean. None of these values gives a diagnosis on its own, but together they sketch a direction.
| Blood value | Detects | What an abnormal result can mean |
|---|---|---|
| CRP | Inflammation | Raised can fit gut inflammation (IBD) or infection; normal makes IBD less likely |
| Ferritin | Iron stores | Low can point to poor absorption (malabsorption), e.g. in celiac disease |
| tTG-IgA | Celiac disease | Raised makes celiac likely, a reason for referral |
| Leukocytes | Infection or inflammation | Raised or lowered can point to an active immune process |
| TSH | Thyroid | Abnormal can speed up or slow down gut activity |
CRP and leukocytes: is there inflammation?
CRP (C-reactive protein) is a protein your liver makes during inflammation. In someone with gut complaints, a raised CRP is a signal that can fit an inflammatory bowel disease such as Crohn's disease or ulcerative colitis, or an infection. CRP is not gut-specific, so the result must always be assessed in context. A normal CRP does not fully rule out gut inflammation, but makes it less likely. In irritable bowel syndrome (IBS), CRP and leukocytes are usually normal, and that very distinction helps your doctor decide whether further investigation is needed.
Ferritin and celiac disease: absorption as the cause
A low ferritin with stomach complaints is an important signal, because it can mean your gut is not absorbing nutrients well. In the Netherlands, celiac disease is a common cause of such malabsorption. The screening test is tTG-IgA (tissue transglutaminase IgA); if it is raised, your GP refers you to a gastroenterologist. Important: this test is only reliable if you are still eating gluten at the time, so do not stop on your own. Read more in gluten intolerance or celiac disease.
The thyroid: an underrated link
The link between your thyroid and your gut is often underrated. An underactive thyroid (hypothyroidism) can slow gut activity and so cause constipation and bloating, while an overactive thyroid can cause diarrhoea. If you have stomach complaints plus fatigue, weight change or temperature sensitivity, having your thyroid checked is wise.
What you can do yourself
Besides blood testing, practical steps help, and the Netherlands Nutrition Centre (Voedingscentrum) and the Dutch College of General Practitioners (NHG) give similar advice here:
- Keep a food diary, so you recognise patterns.
- Eat calmly and chew well, because eating fast and swallowing air worsen bloating.
- Limit known triggers such as carbonated drinks, chewing gum and artificial sweeteners.
- Move after eating, a short walk stimulates gut activity.
- Do not start an elimination diet yourself before celiac disease has been ruled out.
A broad picture comes from a basic health checkup, or more targeted with a celiac disease blood test for a concrete suspicion. If you doubt whether broad intolerance tests help, read food intolerance testing: what works and what does not.
Frequently asked questions
Can a blood test explain all gut complaints?
No. A blood test is a valuable first step, but conditions such as irritable bowel syndrome or a food intolerance are not diagnosed with it. With persistent complaints, your doctor may suggest further investigation.
Do I need to be fasted for a blood test for stomach complaints?
For CRP, ferritin and leukocytes, fasting is not needed. For the celiac test (tTG-IgA) neither, but you must still be eating gluten at the time. Discuss dietary changes with your doctor first.
I already have an IBS diagnosis. Is a blood test still useful?
Yes. IBS is a diagnosis of exclusion. If you have never been tested for celiac disease or inflammation markers, that is still wise, because the symptoms overlap and celiac is regularly missed.
When should I see my GP straight away?
With blood in the stool, unexplained weight loss, persistent vomiting, severe stomach pain, or if you are over 50 and the complaints are new. These are warning symptoms that need prompt assessment.
What you can do now
My advice: use blood to rule out treatable causes such as celiac disease, iron deficiency and thyroid problems, and only then build further. Every blood test result at Vitalcheck includes a professional assessment by a BIG-registered doctor. A blood value is not a diagnosis: always discuss treatment decisions with your GP.
Sources
- NHG guideline on irritable bowel syndrome (IBS). Dutch College of General Practitioners. Accessed 2026.
- Voedingscentrum (Netherlands Nutrition Centre). Stomach complaints and nutrition. Accessed 2026.
- Thuisarts.nl / NHG. I have a bloated feeling. Accessed 2026.
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Testing for food intolerance: what works and what does not
Gluten intolerance or celiac disease: the difference and how to test
