Anemia is diagnosed primarily through a simple blood test called a complete blood count, or CBC. This test measures your hemoglobin level, which is the protein in red blood cells that carries oxygen. You’re generally considered anemic if your hemoglobin falls below 12.0 g/dL for women or around 13.0 g/dL for men, though the threshold is 11.0 g/dL for children. A CBC is often just the starting point. Depending on the results, your provider may order follow-up tests to figure out what type of anemia you have and what’s causing it.
What a Complete Blood Count Reveals
A CBC is the first test ordered when anemia is suspected, and it provides a surprisingly detailed picture of your blood. Beyond hemoglobin, it measures your hematocrit (the percentage of your blood made up of red blood cells) and several values called red blood cell indices. These indices tell your provider about the size, shape, and content of your red blood cells, which helps narrow down the cause of anemia before any additional testing.
One of the most useful values is mean corpuscular volume, or MCV, which measures the average size of your red blood cells. Small red blood cells point toward iron deficiency anemia, the most common type. Large red blood cells suggest a vitamin deficiency, typically B12 or folate. Normal-sized red blood cells with low hemoglobin can indicate chronic disease, kidney problems, or blood loss. The CBC also reports red cell distribution width (RDW), which shows how much variation there is in the size of your red blood cells. A wide range of sizes can be an early clue that something is off even before hemoglobin drops significantly.
You don’t need to fast for a CBC. You can eat and drink normally beforehand. However, if your provider orders additional tests alongside the CBC, such as an iron panel, you may be asked to fast. It’s worth confirming when you schedule the blood draw.
Iron Studies
If your CBC suggests iron deficiency, the next step is usually an iron panel. This group of tests measures how much iron is circulating in your blood, how well your body stores iron, and how efficiently it transports iron to where it’s needed.
The most important test in the panel is ferritin, a protein that reflects your body’s iron stores. A ferritin level below 30 ng/mL is a strong indicator of iron deficiency, catching about 92% of cases while rarely producing a false positive. Levels at or above 100 ng/mL generally rule out iron deficiency. If you have a chronic inflammatory condition like rheumatoid arthritis or inflammatory bowel disease, the picture gets more complicated because inflammation artificially raises ferritin. In those cases, iron deficiency is likely when ferritin is below 50 ng/mL.
The panel also includes total iron-binding capacity, or TIBC, which measures how much room is available on your transport proteins to carry iron. When iron stores are low, your body produces more transport proteins in an attempt to grab whatever iron it can. So low ferritin combined with high TIBC is the classic fingerprint of iron deficiency anemia. Your provider interprets these results together rather than relying on any single number.
Vitamin B12 and Folate Testing
When a CBC shows abnormally large red blood cells, the likely culprits are vitamin B12 or folate deficiency. Both of these vitamins are essential for producing healthy red blood cells, and when levels drop too low, the body makes fewer, oversized cells that don’t function properly. This is called megaloblastic anemia.
A blood test can measure both vitamins directly. B12 levels below 150 ng/L are considered evidence of deficiency, while levels between 150 and 400 ng/L fall into a borderline zone that may need further investigation. For folate, levels below 4.0 mcg/L suggest deficiency.
When results are borderline or unclear, your provider can order two additional markers to help distinguish between the two deficiencies. In folate deficiency, a compound called homocysteine rises while another called methylmalonic acid (MMA) stays normal. In B12 deficiency, both homocysteine and MMA are elevated. The MMA test is considered the most sensitive way to detect B12 deficiency at the cellular level, meaning it can pick up a problem even when your B12 blood levels look borderline.
Reticulocyte Count
A reticulocyte count measures the number of very young red blood cells your bone marrow is releasing into the bloodstream. Think of it as a way to check whether your bone marrow is responding appropriately to anemia. This test helps providers sort anemia into two broad categories: problems with red blood cell production versus problems with red blood cell loss or destruction.
A high reticulocyte count means your bone marrow is working overtime to replace red blood cells. This pattern shows up when you’re losing blood (from heavy periods, a GI bleed, or injury) or when your body is destroying red blood cells faster than it can make them, a condition called hemolytic anemia. A low reticulocyte count, on the other hand, means the bone marrow itself isn’t keeping up. This can point to nutritional deficiencies, aplastic anemia (where the bone marrow fails to produce enough cells), or bone marrow suppression from infection or cancer.
Testing for Inherited Anemias
If standard blood work doesn’t explain the anemia, or if your family background or ethnicity raises the likelihood of a genetic condition, your provider may order hemoglobin electrophoresis. This test applies an electric current to a blood sample, separating the different types of hemoglobin so each one can be measured individually.
It’s the primary test for diagnosing sickle cell disease and thalassemia. In the United States, sickle cell disease is most common among Black and African American individuals. Thalassemia occurs most frequently in people of Italian, Greek, Middle Eastern, South Asian, and African descent. Newborns in the U.S. are automatically screened for hemoglobin disorders as part of standard newborn testing. Adults may be tested if they have unexplained anemia, a family history of hemoglobin disorders, or are planning a pregnancy and want to understand their carrier status.
Physical Signs Your Provider Checks
Before or alongside blood work, your provider will look for physical signs of anemia during an exam. One of the most reliable visual indicators is pallor of the inner eyelid. Your provider pulls down your lower eyelid and checks the color of the tissue lining it. In a healthy person, this tissue is a rich red. In someone with anemia, it looks pale or washed out. Providers also check the color of your palms, nail beds, and skin tone, though these are less reliable across different skin tones. Your heart rate and blood pressure matter too, since the heart pumps faster to compensate when fewer red blood cells are available to carry oxygen.
At-Home Anemia Tests
An FDA-approved at-home hemoglobin test called AnemoCheck Home is available by prescription. It uses a single finger prick: you collect a small blood sample in a test tube, shake it to mix with a solution, then compare the color of the sample to a reference card after two minutes. The color corresponds to a hemoglobin level. In testing, it performed comparably to the professional-grade analyzers used in labs and was more accurate than the WHO’s hemoglobin color scale method.
An at-home test can tell you whether your hemoglobin is low, but it can’t tell you why. If the result suggests anemia, you’ll still need a full CBC and likely follow-up tests through a lab to identify the type and cause. These tests are most useful for people who are already diagnosed and want to monitor their levels between appointments, or for those who want a quick screen before deciding whether to see a provider.