Anemia and iron deficiency: Full guide

What is anemia?

Anemia means your blood has fewer healthy red blood cells than normal, or less hemoglobin. Hemoglobin is the protein inside red blood cells that carries oxygen from your lungs to the rest of your body. When it is low, your body gets less oxygen.

Anemia is not a disease by itself. It is a sign that something else is going on. So the most important step is finding out why it is happening. Anemia is not cancer, and most causes are common and treatable.

The most common cause around the world is iron deficiency. This means your body does not have enough iron to make hemoglobin. Iron is a mineral that comes from food. Your body cannot make it.

In adults, iron deficiency is most often caused by slow blood loss. This can be from heavy periods or from bleeding in the stomach or bowel that you may not see. Not getting enough iron from food, or not absorbing it well, can also cause it. Pregnancy uses up a lot of iron too.

Anemia can make you feel tired, weak, short of breath, or dizzy. Your heart may race. Some people have no symptoms at all, and anemia is found on a routine blood test. Anemia is not a normal part of getting older, so it should always be checked.

Common kinds of anemia

Iron deficiency anemia

The most common kind. The body runs low on iron, so it makes small, pale red blood cells. It is usually caused by blood loss, low iron in the diet, poor absorption, or pregnancy.

Iron deficiency without anemia

Your iron stores are low, but your hemoglobin is still normal. You can still feel tired or have restless legs. It is common and can be treated.

Vitamin B12 deficiency

B12 is a vitamin needed to make red blood cells and keep nerves healthy. Low B12 makes large red blood cells. It can also cause numbness, tingling, or balance and memory problems. It is common after stomach surgery, with some stomach conditions, with a strict vegan diet, and with some medicines.

Folate deficiency

Folate (folic acid) is another vitamin needed to make red blood cells. Low folate also makes large red blood cells. It can come from a poor diet, heavy alcohol use, or some medicines.

Anemia of chronic disease (anemia of inflammation)

Long-term conditions like infections, arthritis, bowel disease, or cancer can cause inflammation. Inflammation makes the body lock iron away so it cannot be used, even if there is enough. Treating the underlying condition is the main fix. Some people have this and iron deficiency at the same time.

Anemia from kidney disease

Healthy kidneys make a hormone called erythropoietin (EPO) that tells the bone marrow to make red blood cells. Damaged kidneys make less of it. This kind of anemia is often treated with iron and EPO shots.

Anemia from blood loss

Sudden heavy bleeding, such as from an injury or a bleeding ulcer, can cause anemia quickly. Slow, hidden bleeding causes it over months and often leads to iron deficiency.

Hemolytic anemia

Red blood cells break down faster than the body can replace them. Causes include immune problems, some inherited conditions, infections, and certain medicines. It is less common and needs special tests.

Inherited anemias

Some people are born with conditions that affect red blood cells, such as thalassemia trait or sickle cell disease. Thalassemia trait also makes small red blood cells, so it can look like iron deficiency on a blood count.

Tests you may have

Complete blood count (CBC)

A basic blood test that measures hemoglobin and the size of your red blood cells. Small cells point toward iron deficiency. Large cells point toward B12 or folate problems, liver disease, alcohol, or other causes.

Ferritin

Ferritin is a protein that stores iron. The blood level shows how much iron your body has saved up. A low ferritin means iron deficiency. It is the first iron test to drop. Inflammation can raise ferritin, so a normal result does not always rule out low iron.

Iron, TIBC, and transferrin saturation

These blood tests show how much iron is moving in your blood and how much room there is to carry more. They help tell iron deficiency apart from anemia of inflammation.

Reticulocyte count

Reticulocytes are young red blood cells. This test shows whether your bone marrow is making enough new cells. It helps tell blood loss or breakdown apart from a problem making cells.

Vitamin B12 and folate levels

Blood tests to check for these vitamins. Sometimes extra tests called methylmalonic acid (MMA) and homocysteine are used when the result is borderline.

Colonoscopy and upper endoscopy

A thin tube with a camera looks inside the large bowel (colonoscopy). A similar test looks at the food pipe, stomach, and upper small bowel (upper endoscopy). You get medicine to help you relax. These tests look for hidden bleeding. They are usually advised for men and for women past menopause with iron deficiency.

Celiac disease test

A blood test for celiac disease, a condition where gluten damages the small bowel. It can stop iron from being absorbed. It is often checked when the cause of iron deficiency is not clear.

H. pylori test

A breath, stool, or biopsy test for a stomach germ called H. pylori. It can cause ulcers and stomach inflammation that lower iron absorption.

Gynecology visit

For women with heavy periods, a visit with a gynecologist can look for causes like fibroids and help control the bleeding.

Blood smear

A drop of blood is looked at under a microscope. The shape of the cells can give clues to the cause of anemia.

How serious it is

Doctors often describe anemia as mild, moderate, or severe, based on your hemoglobin level. But how you feel, how fast the anemia came on, and your other health problems matter just as much.

Anemia that develops slowly is often well tolerated, because the body adjusts. Anemia that comes on fast, from sudden bleeding, can be serious even at the same hemoglobin level.

The cause matters most. Finding and treating the reason for the anemia is the key to getting better and staying better.

Mild anemia

Hemoglobin is a little below normal. Many people have no symptoms or feel a bit tired. It still deserves a search for the cause.

Moderate anemia

More symptoms are common, such as tiredness, shortness of breath with activity, and a fast heartbeat. Treatment is usually given as an outpatient.

Severe anemia

Hemoglobin is very low. People may feel very weak, dizzy, or short of breath at rest, or have chest pain. Some need a blood transfusion or IV iron sooner.

Higher-risk situations

Anemia can be harder on people with heart or lung disease, older adults, and pregnant women. Your care team may treat sooner or more closely in these cases.

Ongoing blood loss

If bleeding is still happening, anemia can keep coming back until the source is fixed. Black or bloody stools need quick attention.

Lab tests to know

A few lab numbers help your care team understand your anemia and track your progress. Normal ranges vary a bit between labs. Ask your care team to explain your own results.

Hemoglobin

The main number for anemia. For most adults, anemia means hemoglobin below about 13 in men and below about 12 in women who are not pregnant. It should start to rise within a few weeks of good treatment.

MCV (red cell size)

Shows the average size of your red blood cells. Small cells suggest iron deficiency or thalassemia trait. Large cells suggest B12 or folate deficiency, alcohol, liver or thyroid problems, or a marrow problem.

RDW

Shows how much your red blood cells vary in size. It often rises early in iron deficiency.

Ferritin

Your iron savings account. A level below about 30 usually means iron deficiency. In people with inflammation, kidney disease, or heart failure, iron deficiency can be present even with a higher ferritin.

Transferrin saturation (TSAT)

The percent of your iron-carrying protein that is filled with iron. A low value supports iron deficiency. It is low in anemia of inflammation too.

TIBC

Total iron binding capacity. It tends to be high in iron deficiency and low in anemia of inflammation. This helps tell the two apart.

Reticulocyte count

Young red blood cells. This number usually rises within about a week of starting iron, which is an early sign that treatment is working.

Phosphate

Some IV iron products can lower phosphate, a mineral needed for strong bones. Your care team may check it, especially if you need more than one course.

Main treatments

Finding and fixing the cause

This is the most important part of treatment. It may mean treating heavy periods, healing an ulcer, removing a polyp, treating celiac disease, or changing a medicine. Iron alone will not fix anemia for good if bleeding continues.

Iron pills

Iron by mouth is the first choice for most people. Common forms are ferrous sulfate, ferrous gluconate, and ferrous fumarate. Newer forms may be easier on the stomach. Your care team will tell you which one and how much to take.

Taking iron pills the right way

Iron is best absorbed on an empty stomach, with a little vitamin C such as orange juice. Do not take it with milk, calcium, coffee, tea, or antacids. Many people take iron every other day, which can help the body absorb more and cause fewer stomach problems. Ask your care team what schedule is right for you.

How long iron treatment lasts

Hemoglobin often starts to rise in 2 to 4 weeks. After your blood count is normal, you usually keep taking iron for about 3 more months. This refills your iron stores. Your care team will recheck your blood to decide when to stop.

IV iron

Iron given through a vein. It works faster and fills iron stores in 1 to 5 visits, depending on the product. It is used when pills cause too many side effects, do not work, or cannot be absorbed. It is also common in kidney disease, bowel disease, heart failure, and after weight loss surgery. It may be used later in pregnancy or when iron is needed quickly.

Vitamin B12

B12 can be given as shots or as pills. Some people, such as those whose stomach cannot absorb B12, need it for life. Nerve symptoms improve best when treatment starts early.

Folic acid

Folate is given as a pill. Your care team will usually check B12 first, because folic acid alone can hide B12 deficiency while nerve damage gets worse.

Treating anemia of chronic disease

The main treatment is controlling the condition causing inflammation. If iron deficiency is also present, IV iron may help. People with kidney disease may also get shots that help the marrow make red blood cells.

Blood transfusion

Getting donated red blood cells through a vein. It raises hemoglobin quickly. It is used for severe anemia, active heavy bleeding, or serious symptoms. Most stable people with iron deficiency do not need one.

Eating iron-rich foods

Meat, poultry, fish, beans, lentils, and leafy greens contain iron. Iron from meat is absorbed best. Food helps keep iron up, but it is usually not enough by itself to fix iron deficiency anemia.

Treatment side effects and what helps

Upset stomach and nausea from iron pills

Very common. Taking iron every other day, at a lower amount, or with a small snack can help. A bit less iron may be absorbed, but that is often okay. Switching to a different form of iron may also help. Talk to your care team before stopping.

Constipation

Iron pills often cause constipation. Drink plenty of fluids, eat fiber, and stay active. Ask your care team about a stool softener.

Dark or black stools

Iron normally turns stool dark green or black. This is expected. But black, sticky, tar-like stools, or stools with red blood, can mean bleeding. Call your care team if you are not sure.

Metallic taste and stained teeth

Some people notice a metal taste. Liquid iron can stain teeth, so drink it through a straw and brush after.

Infusion reactions from IV iron

Serious allergic reactions are rare with newer IV iron products. Some people get flushing, muscle aches, or chest tightness during the infusion. You will be watched during and for a short time after. Tell the nurse right away if you feel unwell.

Achy joints or flu-like feeling after IV iron

Some people feel achy or tired for a day or two. Rest and fluids help. Ask your care team what pain medicine is safe.

Low phosphate after some IV iron

Ferric carboxymaltose (Injectafer) often lowers phosphate. It is usually mild, but with repeat doses it can cause bone pain, weakness, or weak bones. If you need iron again, your care team may check phosphate or choose a different product.

MRI changes after ferumoxytol

Ferumoxytol (Feraheme) can change how MRI pictures look for up to about 3 months. Tell anyone ordering an MRI that you had it.

Skin staining

Rarely, IV iron leaks out of the vein and leaves a brown stain on the skin. Tell the nurse right away if the IV site hurts or swells.

Living with and after anemia

Most people start to feel better within a few weeks of the right treatment. Energy, breathing, and focus often improve before your iron stores are fully refilled. Keep taking your treatment for as long as your care team advises.

Follow-up blood tests show whether treatment is working. If your hemoglobin does not rise as expected, your care team will look for reasons. These include ongoing bleeding, poor absorption, missed doses, or another cause of anemia.

If you had iron deficiency, the cause may come back. Heavy periods, bowel disease, weight loss surgery, and frequent blood donation can drain iron again. Ask your care team how often to check your blood.

Some symptoms are clues to low iron. Examples are craving ice, restless legs at night, spoon-shaped nails, or sores at the corners of the mouth. These often get better as iron is replaced.

Eat a balanced diet with iron-rich foods. If you are vegetarian or vegan, plan meals with beans, lentils, and iron-fortified foods, and pair them with vitamin C. Ask about B12 if you eat no animal foods.

Do not start iron pills on your own long term without testing. Too much iron can build up and harm the body. Keep iron pills away from children, because an overdose can be very dangerous for them.