The short answer
Anemia has many causes. When iron is low, doctors look for a reason, including slow bleeding in the gut. Iron pills treat the numbers, not the cause, so ask what the plan is to find it.
Anemia means too few healthy red blood cells. Causes include low iron, low B12 or folate, long-term disease, and blood loss.
MedlinePlus says treatment should be directed at the cause of the anemia.
Heavy periods, ulcers and bleeding in the digestive tract can cause blood loss. Even small amounts of bleeding over a long time can lead to anemia.
Ferritin is a blood test of the body's iron stores. A low result suggests low iron stores. Ask your team how to read your result.
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The whole article, with every detail and caution.
This page is for people told they have anemia (low red blood cells) with no clear cause. It covers when to get help, common causes, and why a doctor may look for a source of bleeding.
When to get help
Call 911 or go to the emergency room now for any of these.
- Vomiting blood or coffee-ground material.
- Black, tarry stools.
- Chest pain.
- Fainting.
- Breathlessness at rest.
MedlinePlus says to contact your doctor about any symptoms of anemia or unusual bleeding. Ask for a faster review if anemia comes with bleeding you can see, weight loss, a change in bowel habits, or trouble swallowing.
Anemia found on a routine blood test is not usually an emergency, but it should not be left open-ended. Ask your team when the cause will be looked into.
What anemia usually turns out to be
Anemia means the body does not have enough healthy red blood cells. These cells carry oxygen. MedlinePlus lists these common causes:
- low iron, vitamin B12 or folic acid
- long-term disease, such as kidney disease or cancer
- blood loss from heavy periods or ulcers
- bone marrow disorders
- inherited conditions such as sickle cell disease
Most anemia is not a sign of cancer. But MedlinePlus notes that even small amounts of bleeding in the digestive tract over a long time can lead to anemia. That is one reason doctors look for the cause.
Checking iron
Doctors usually start with a complete blood count and blood levels of iron, B12 and folic acid. Ferritin is a protein that stores iron, and the ferritin test indirectly measures your iron stores. MedlinePlus says low ferritin suggests low iron stores. Some conditions, such as autoimmune disease and liver disease, can raise ferritin. Ask your team how to read your result.
Iron treats the numbers, not the cause
Iron supplements are the main treatment for iron deficiency anemia, according to MedlinePlus. It also says outcomes depend on finding and treating the underlying cause. If you take iron, ask what the plan is to learn why your iron was low. If anemia comes back after iron is stopped, tell your team.
Tests that look for bleeding
If a bleeding source is a concern, your team may suggest a colonoscopy. MedlinePlus describes it as a thin tube with a camera passed through the rectum to look at the lower digestive tract. Ask your team whether other tests, such as an upper endoscopy, make sense for you and how soon they can be done.
Sources
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Common questions
What does a ferritin test show?
MedlinePlus says ferritin is a protein that stores iron, and the test indirectly measures the iron stored in your body. Low ferritin suggests low iron stores. Ask your team how your own result fits with your other tests.
I have heavy periods. Do I still need more testing?
Heavy periods can cause iron loss, and MedlinePlus lists them as a cause of anemia. Whether you need other tests is a decision for you and your care team. Ask what they recommend and why.
Why not just take iron and see what happens?
Iron can raise your numbers, but MedlinePlus says treatment should be directed at the cause of the anemia. Ask your team how they plan to find the cause.
What does a colonoscopy involve?
MedlinePlus describes colonoscopy as a thin tube with a camera, passed through the rectum, to look at the lower digestive tract. Ask your team about preparation and sedation.
Both tests were normal. What now?
Ask your team what else could explain the anemia and what follow-up blood tests they want. Report any new bleeding, black stools or other symptoms right away.
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Written by: Cancer ExplainedSources last checked: 2026-10-02 what this meansLast updated: 2026-08-10Next planned review: 2027-08-03
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Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes, and this is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Source checked — This page was written with AI assistance and then compared with the sources listed on it, looking for statements those sources do not back up. That check is not a sentence-by-sentence record and can miss errors. It is not a medical review, and it does not confirm the page is complete or right for your situation.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
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