What to explain
Ask whether the blood test shows anemia and what may have caused it.
My blood tests show anemia, or my symptoms make me wonder whether I have it. I want help understanding whether my hemoglobin is low for my age and, if relevant, my stage of pregnancy. I also want to know what the other parts of my blood count mean and what may have caused the anemia. Could we check for blood loss, low iron, low vitamin B12 or folate, kidney disease, inflammation, an inherited blood condition, or another blood problem? I do not want to start a high-dose iron supplement until a test shows whether I am low in iron.
Questions to take in
Ask these questions about your anemia and what may have caused it.
- Is my hemoglobin below the expected range for someone my age and, if relevant, my stage of pregnancy? Is the anemia mild, moderate, or severe? Did it start recently or has it been present before?
- What do my MCV (average red-cell size), RDW (variation in red-cell size), reticulocyte count (new red cells), white cells, platelets, and blood smear show about why I have anemia?
- Do my tests confirm low iron? Could inflammation be making ferritin look higher, and would transferrin saturation or another iron test help show whether I am low in iron?
- What is the most likely cause of my anemia? Could it be menstrual or other blood loss, too little iron or vitamins, poor absorption, kidney disease, inflammation, red-cell breakdown, an inherited condition, or a bone-marrow problem?
- If iron-deficiency anemia is confirmed, how do my age, sex, periods, symptoms, and family history affect the next step? Do I need tests for bleeding from the stomach, bowel, urinary tract, or reproductive system, or a test for celiac disease?
- What is causing the anemia, how will we treat that cause, which blood test should we repeat, and when should my blood count begin to improve?
- If I am low in iron, which foods could help? If I need treatment, which iron product, amount, timing, or intravenous (IV) treatment is safe for me?
- Which symptoms or changes in my blood test mean I should seek help before the next routine appointment?
CBC, iron, vitamin, and bleeding checks
What each blood test can tell your doctor.
A complete blood count (CBC) can show whether you have anemia. Ferritin and iron studies can show iron deficiency. Vitamin B12 and folate tests can find vitamin deficiencies. Kidney tests, inflammation markers, a reticulocyte count, and a blood smear may help identify why anemia developed. Your doctor will also ask about periods, pregnancy, surgery, blood donation, and bleeding from the stomach, bowel, or urinary tract.
CBC + CMP Blood Test Bundle
The CBC shows hemoglobin, the red blood cell count, and measures of red blood cell size. It also counts white blood cells and platelets. The CMP checks kidney function, electrolytes, glucose, and blood proteins. Kidney disease can cause anemia. Changes in other CMP results may show a separate health problem, but neither panel identifies the cause of anemia by itself.
Read the test guideMCV (Mean Corpuscular Volume) Blood Test
MCV shows the average size of your red blood cells. A low, normal, or high result can help your doctor decide which causes to check next, but MCV cannot identify the cause by itself.
Read the test guideFerritin
Ferritin estimates how much iron your body has stored. A low result supports iron deficiency. Inflammation or illness can raise ferritin, so a ferritin result within the expected range may not rule out iron deficiency.
Read the test guideIron studies (transferrin, TIBC, and transferrin saturation)
Transferrin saturation, total iron-binding capacity (TIBC), transferrin, and serum iron show how the blood carries iron. Your doctor reads the results together because serum iron changes during the day.
Ask your doctorReticulocyte count and blood smear
A reticulocyte count shows whether your bone marrow is making new red blood cells. A blood smear shows the cells' size, shape, and color. Both may be used when anemia is severe or its cause is unclear.
Ask your doctorVitamin B12
A vitamin B12 test checks whether low B12 could be causing anemia, numbness, balance problems, memory changes, or fatigue. Low B12 can affect nerves even when hemoglobin and MCV are normal.
Read the test guideFolate
A folate test checks whether low folate could be causing anemia with large red blood cells. Doctors usually consider folate and vitamin B12 together because folate can improve the blood count without treating nerve problems caused by low B12.
Read the test guidetTG-IgA Celiac Blood Test
The tTG-IgA blood test checks for celiac disease, which can stop the body from absorbing iron properly. A total IgA test is often done at the same time to make sure the tTG-IgA result is reliable. The test usually needs to be done while you are still eating gluten, unless a clinician tells you otherwise.
Read the test guideBefore the appointment
Bring these results and notes to your appointment.
Bring the complete blood count (CBC) report, not only the hemoglobin line. Include the date, laboratory ranges, hematocrit, red-cell count, MCV (average red-cell size), RDW (how much the sizes vary), white cells, and platelets.
Bring any ferritin result and other iron results, such as serum iron, transferrin, TIBC, or transferrin saturation. Also bring results for vitamin B12, folate, reticulocytes, a blood smear, kidney or thyroid function, inflammation, or celiac disease.
Mention any bleeding: heavy or longer periods, bleeding between periods, bleeding during or after pregnancy, black or bloody stool, blood in urine, nosebleeds, surgery, injury, or blood donation.
Say when the symptoms began and how they changed. Include real examples of breathlessness, racing heart, dizziness, fainting, headaches, weakness, feeling cold, craving ice, restless legs, numbness, balance trouble, or difficulty concentrating.
Mention every prescription, over-the-counter medicine, and supplement you take. Include aspirin, ibuprofen or other anti-inflammatories, blood thinners, acid reducers, metformin, iron, vitamin B12, and folate.
Mention if you have celiac disease, inflammatory bowel disease, a history of stomach or bowel surgery, kidney disease, ongoing inflammation, cancer treatment, restricted eating, or unplanned weight loss.
Describe the foods you usually eat in a normal week, including meat, seafood, beans, lentils, tofu, leafy vegetables, and fortified foods. This helps the doctor check whether your diet could be affecting iron, vitamin B12, or folate. It is not a test of whether you ate well enough.
Say if you or a family member has thalassemia, sickle cell disease or trait, G6PD deficiency (an inherited red-cell condition), a bleeding disorder, or another inherited blood condition.
Also bring notes about symptoms, bleeding, medicines, pregnancy, and any iron or vitamin tests collected near the same date.
How the doctor assesses this
Signs that anemia may be contributing to the brain fog
- A current CBC shows hemoglobin below the laboratory's expected range for your age and, if relevant, stage of pregnancy.
- Brain fog happens with breathlessness, dizziness, racing heart, weakness, headaches, ice craving, restless legs, or difficulty with ordinary physical activity.
- Heavy periods, pregnancy, recent bleeding, surgery, blood donation, stomach or bowel symptoms, a restricted diet, kidney disease, inflammation, or family history make it more important to check the cause.
Signs that the brain fog may have another cause
- A current CBC shows hemoglobin within the laboratory's expected range for the person's age and, if relevant, stage of pregnancy.
- The brain fog began before the hemoglobin fell or stays the same while the anemia and its cause improve.
- The blood tests and medical history do not show anemia, low iron, a vitamin problem, kidney disease, inflammation, bleeding, or an inherited blood condition that explains the symptoms.
- The brain fog starts or worsens after poor sleep, a medicine change, an infection, or a migraine while the hemoglobin stays unchanged. A thyroid problem, blood sugar change, or low blood pressure may also explain the symptoms better than anemia.
- Symptoms get worse while the hemoglobin and the cause of the anemia are improving. The doctor needs to look for another cause of the symptoms too.
What to understand before choosing care
What your doctor needs to find out about the anemia.
- Anemia means there is less hemoglobin, the part of red blood cells that carries oxygen, than expected. The word anemia does not tell you why this happened.
- Iron deficiency is one possible cause. Blood loss, vitamin B12 or folate deficiency, kidney disease, inflammation, inherited blood conditions, red-cell breakdown, and bone-marrow problems can also cause anemia.
- Your doctor will read the whole CBC, not only hemoglobin. The size and variation of red blood cells, white-cell and platelet counts, reticulocyte count, and blood smear can help show which causes need checking.
- Hemoglobin shows whether you have anemia. Ferritin and iron studies help show whether low iron is the cause. A person can have low iron without anemia, or anemia without low iron.
- Treatment depends on why the anemia happened. Taking iron without checking for bleeding, poor absorption, or a cause unrelated to iron can delay the treatment you need.
What the research found
How to read the hemoglobin and ferritin numbers in this handout.
The World Health Organization (WHO) publishes numbers that help doctors decide whether a hemoglobin result counts as anemia. They are not goals that everyone should try to reach. The laboratory range, altitude, smoking, pregnancy, hydration, symptoms, and speed of change can affect what the result means.
Ferritin helps show how much iron the body has stored. A 2025 JAMA review says a result below 30 ng/mL usually points to low iron when inflammation is not present. For adults who already have anemia, the American Gastroenterological Association (AGA) uses below 45 ng/mL to help identify iron deficiency during a check for blood loss from the stomach or bowel. These numbers help identify low iron. They are not goals that everyone should try to reach, such as 50, 70, or 100.
The 2025 JAMA review lists fatigue, trouble concentrating, shortness of breath, lightheadedness, and tiring sooner during exercise among possible iron-deficiency symptoms.
A 2025 review pooled 18 studies with 1,408 participants, mainly menstruating adults and young people without anemia. Iron improved some fatigue and thinking measures in iron-deficient groups, but not attention or depression. It doesn't support taking iron when no test has shown a deficiency.
Food can improve iron intake, but it cannot tell you why anemia happened. Iron supplements can cause side effects, interact with medicines, and be harmful in excess. Keep them away from children. Before taking iron, ask a clinician whether you need it and whether bleeding or poor absorption also needs treatment.
How age, sex, and pregnancy change the hemoglobin numbers.
Children need blood-test ranges for their exact age and assessment by a child-health clinician. WHO's 2024 guide gives age-specific anemia cutoffs for children. They are below 105 g/L at 6 to 23 months, below 110 g/L at 24 to 59 months, and below 115 g/L at 5 to 11 years. Adult numbers and supplement plans are for adults, not children.
For ages 12 to 14, WHO uses below 120 g/L for both boys and nonpregnant girls. Growth, menstruation, diet, symptoms, family history, and the laboratory report still matter.
During pregnancy, WHO uses below 110 g/L in the first trimester, below 105 g/L in the second, and below 110 g/L in the third. A doctor should also ask about bleeding during or after pregnancy and choose treatment that is safe during pregnancy.
For nonpregnant adults ages 15 to 65, WHO uses below 120 g/L for women and below 130 g/L for men. Heavy periods are a common cause of iron loss. When men or women who have been through menopause have confirmed iron-deficiency anemia, doctors often check for bleeding from the stomach or bowel.
Anemia is not an expected part of getting older. In older adults, kidney disease, inflammation, stomach or bowel bleeding, poor intake, medicines, cancer treatment, and bone-marrow conditions may need attention.
If the answer is no
If your doctor will not order every anemia test at once
Doctors check for anemia in steps. The National Heart, Lung, and Blood Institute says a complete blood count is the usual first test. Your history, exam, and blood-cell results decide whether you need iron tests, a blood smear, or a referral.
What changes the answer
- Ask what the CBC already shows. Request the hemoglobin, hematocrit, red-cell count and cell-size results, then ask whether they point toward anemia or a particular next test.
- Explain why iron deficiency is plausible. Bring information about bleeding, menstrual history, diet, pregnancy, digestive symptoms, surgery and previous iron results. These details help decide whether ferritin and iron studies belong next.
- Ask whether the question is anemia or low iron without anemia. Those are related but different questions, so a normal hemoglobin does not answer every concern about iron stores.
- Agree on a follow-up trigger. Ask what change in symptoms or results would justify repeat blood work, investigation for blood loss or referral to a blood specialist.
United States, United Kingdom, and Australia
Who to contact about Anemia and Brain Fog.
US United States
Take the full report to primary care. Ask whether you have anemia and whether low iron is the cause. Ask if the doctor needs to check for bleeding, poor absorption, kidney disease, inflammation, or an inherited blood condition.
- The CBC and iron tests answer separate questions. The CBC shows whether anemia is present. Ferritin and related iron results help show whether low iron may be the cause.
- In adults who already have anemia, a ferritin below 45 ng/mL helps show iron deficiency. The American Gastroenterological Association (AGA) recommends that cutoff.
- If tests confirm iron-deficiency anemia, your doctor may ask about periods, stomach or bowel bleeding, blood in urine, blood donation, diet, and problems absorbing iron. Whether you need an endoscopy (a camera test of the stomach or bowel) depends on your age, sex, symptoms, and preferences after you discuss the options together.
UK United Kingdom
Ask the GP what may have caused the anemia. Bring the full blood count, bleeding notes, medicines, diet, and earlier results. Ask whether you need iron or vitamin tests, a FIT stool test for hidden blood, celiac testing, or a specialist.
- A GP can arrange a full blood count and review the result, symptoms, diet, periods, medicines, pregnancy, and signs of blood loss.
- If the cause is unclear, a GP may arrange a stool test for hidden bowel blood or refer you for more checks. Not everyone needs the same tests.
- Vitamin B12 and folate deficiency are different causes of anemia and need their own assessment and treatment.
AU Australia
Take the complete report to a GP. Ask whether you have anemia, whether low iron is the cause, what may have caused the low iron or anemia, and when to repeat the blood tests.
- A full blood examination and iron studies are used together. Serum iron alone is not a useful test for diagnosing iron deficiency.
- Lifeblood uses ferritin below 30 micrograms per litre in adults as a sign of low iron. Transferrin saturation below 20% means little iron is available to make red blood cells. Inflammation can make ferritin look higher than it would otherwise.
- A doctor still needs to find out why the iron is low. Possible reasons include blood loss, pregnancy, diet, blood donation, poor absorption, kidney disease, inflammation, or another blood condition.
Safety
Show how it affects daily life
- One or two real examples: walking to the car, stairs, showering, twenty minutes of work, cooking, following a conversation.
- Whether the brain fog, breathlessness or weakness stays constant, and whether periods, blood loss, pregnancy, surgery, illness or missed meals worsen it.
- When dizziness, breathlessness or a racing heart happens, and whether it lands with the brain fog.
- At review the question is whether daily tasks got easier as the blood count came up.
- Do not push through chest pain, fainting, severe breathlessness, or a racing heartbeat to prove that symptoms are real. Those symptoms need medical assessment.
- If iron deficiency is confirmed, meat, seafood, beans, lentils, tofu, fortified grains, and vitamin C-rich foods can add iron to your diet. Food cannot stop bleeding or correct every problem absorbing iron.
Source checked
Sources behind this handout.
- 01
World Health Organization. Guideline on haemoglobin cutoffs to define anaemia in individuals and populations. 2024.
Source - 02
American Society of Hematology. Iron-Deficiency Anemia.
Source - 03
American Gastroenterological Association. Gastrointestinal evaluation of iron deficiency anemia.
Source - 04
Auerbach M et al. Iron Deficiency in Adults: A Review. JAMA. 2025. PMID: 40159291.
DOI - 05
Fiani D et al. Psychiatric and cognitive outcomes of iron supplementation in non-anemic children, adolescents, and menstruating adults. Neurosci Biobehav Rev. 2025. PMID: 40945632.
DOI - 06
NHS. Iron deficiency anaemia.
Source