Blood tests for low iron and anemia
For people with low iron or anemia, including people with heavy periods and people who give blood often.
11 tests explainedAI-verified against cited sources. Awaiting expert reviewLast reviewed 2026-10-19
Iron runs low in stages. Iron stores, measured by ferritin, fall first, and hemoglobin drops only later, so you can be low on iron without being anemic. Periods are a common reason in people who menstruate, and regular blood donation is another. Guidelines start with hemoglobin and ferritin, add transferrin saturation and CRP when inflammation may be affecting ferritin, and look at red cell size, B12, folate and celiac disease to sort out other causes.
The tests that matter most
Most important first. Each one links to its full page, where the note for this group sits near the top.
Ferritin
BSG calls ferritin the single most useful marker of iron deficiency anemia. AGA recommends a cutoff of 45 ng/mL rather than 15 when ferritin is used to confirm low iron in someone with anemia. BSG notes that most labs print a lower limit between 15 and 30 µg/L (the same numbers in ng/mL), so 45 sits above it.
Sources: British Society of Gastroenterology (2021) and American Gastroenterological Association (2020)
- Men, 20–59
- 30–400 ng/mL
- Men, 60+
- 31–409 ng/mL
Hemoglobin
Hemoglobin shows whether low iron has led to anemia. BSG notes that hemoglobin usually starts to rise within 2 weeks of starting iron by mouth when low iron is the cause, so it is the main number used to follow the response.
- Men, 16+
- 13–17.7 g/dL
- Women, 16+
- 11.1–15.9 g/dL
Transferrin Saturation
BSG notes that transferrin saturation can help when ferritin may be falsely normal, for example during inflammation. A low value is one of the standard blood signs of iron deficiency.
- Usual adult range
- 15–55 %
C-Reactive Protein (CRP, incl. hs-CRP)
Ferritin rises with inflammation, so a CRP measured alongside ferritin helps show whether ferritin can be taken at face value. BSG lists CRP with transferrin saturation and red cell measures as tools for this.
- Usual adult range
- 0–5 mg/L
Total Iron-Binding Capacity (TIBC)
TIBC tends to rise when iron runs low. BSG lists a raised TIBC, along with low ferritin, low transferrin saturation and low serum iron, among the blood signs of iron deficiency.
- Usual adult range
- 250–450 µg/dL
Iron, Serum
Serum iron is part of the usual iron studies, along with TIBC and transferrin saturation. BSG lists a low serum iron among the signs of iron deficiency, but ferritin is the more useful single test.
- Men, 18+
- 38–169 µg/dL
- Women, 18–59
- 27–159 µg/dL
Mean Corpuscular Volume (MCV)
Low iron tends to make red cells smaller (low MCV) and paler (low MCH). BSG notes these changes are less reliable alongside chronic illness, thalassemia or low B12 or folate, and that thalassemia can cause small cells even when iron studies are normal.
- Usual adult range
- 80–100 fL
Reticulocyte Hemoglobin Content (CHr / Ret-He)
Reticulocyte hemoglobin shows how much iron is reaching the newest red cells. BSG notes that a low value, once thalassemia trait is ruled out, is a sign of iron restriction, and that a rise on day 4 of iron treatment is an early sign of response.
- Usual adult range
- 30–37.6 pg
Vitamin B12 (Cobalamin)
Low B12 can also cause anemia. BSG notes that it can hide the small-cell pattern of low iron and is one of the reasons iron treatment may not seem to work.
- Usual adult range
- 232–1,245 pg/mL
Folate (Vitamin B9), Serum
Low folate can also cause anemia. BSG notes that it can hide the small-cell pattern of low iron and is one of the reasons iron treatment may not seem to work.
- Usual adult range
- 3 and above ng/mL
Tissue Transglutaminase (tTG) IgA
In the UK, celiac disease is the most common cause of poor iron absorption, BSG notes. It recommends routine celiac testing in iron deficiency anemia, where celiac disease is found in 3% to 5% of cases. AGA suggests celiac blood tests first in adults with iron deficiency anemia and no symptoms when celiac disease is plausible.
Sources: British Society of Gastroenterology (2021) and American Gastroenterological Association (2020)
- Usual adult range
- 0–10 U/mL
Ranges shown are the usual adult ranges labs print. The range on your own report is the one your result is judged against.
Getting results you can compare
- BSG suggests checking for a hemoglobin response within the first 4 weeks of taking iron by mouth. A good rise within about 2 weeks strongly suggests that low iron was the cause.
- If ferritin is borderline and there is an inflammatory condition, BSG notes that CRP and transferrin saturation can help make sense of it.
Good to know
- Inflammation raises ferritin, so it can look normal during an inflammatory illness even when iron is low. BSG adds that a ferritin above 150 µg/L makes true iron deficiency unlikely, even with inflammation. Labs print ferritin in ng/mL or µg/L, and the number is the same in both, so 150 µg/L is 150 ng/mL.
- Heavy periods are a common cause of low iron, and low iron can come with a normal hemoglobin. In one study of young women with heavy periods that BSG cites, over half had low iron stores but only a quarter were anemic.
Sources: British Society of Gastroenterology (2021) and NHLBI (2022)
- Iron depletion is common in blood donors, especially women and frequent donors. Blood centers check hemoglobin before donating, but hemoglobin is a poor stand-in for iron stores, so a donor can pass that check and still be low on iron.
Questions you could ask
- How should we read my ferritin alongside my CRP and transferrin saturation?
- When should we recheck my hemoglobin and ferritin?
- Could heavy periods, blood donation or my diet explain low iron?
- Would a celiac blood test make sense for me?
- Are my B12 and folate worth checking too?
Sources
- British Society of Gastroenterology guidelines for the management of iron deficiency anaemia in adults, British Society of Gastroenterology (2021)
- Gastrointestinal evaluation of iron deficiency anemia, American Gastroenterological Association (2020)
- Anemia: Iron-Deficiency Anemia, NHLBI (2022)
- Laboratory and Genetic Assessment of Iron Deficiency in Blood Donors, Clinics in Laboratory Medicine (2015)
AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-19. How we build and check these pages.
Educational information, not medical advice. Blood Test Tracker doesn’t diagnose or treat, and it doesn’t replace your clinician. Talk with your clinician before changing medications, supplements or care.