Anemia is checked primarily through a simple blood test called a complete blood count, or CBC, which measures your hemoglobin, hematocrit, and red blood cell size. This single test is the starting point for nearly every anemia diagnosis. But depending on what the CBC reveals, your doctor may order follow-up tests to pinpoint the cause, whether that’s low iron, a vitamin deficiency, or something else entirely.
Signs You Can Spot at Home
Before any blood work, your own body offers clues. The physical signs of iron deficiency anemia include pale inner eyelids (you can gently pull down your lower lid and check if the tissue looks washed out rather than pink-red), unusually pale palm creases, and spoon-shaped nails that curve upward at the edges instead of arching downward. Cracks at the corners of your mouth and a swollen, sore tongue are also common signs.
Beyond what you can see, pay attention to how you feel. Persistent fatigue that doesn’t improve with rest, shortness of breath during normal activities like climbing stairs, dizziness when standing up, cold hands and feet, and a fast or irregular heartbeat are all symptoms worth noting. None of these on their own confirm anemia, but several together are a strong reason to get tested.
The Complete Blood Count
A CBC is a routine blood draw from your arm that measures multiple components of your blood at once. For anemia, three numbers matter most:
- Hemoglobin: the oxygen-carrying protein in your red blood cells. In adults, anemia is generally defined as hemoglobin below 12 g/dL in women and below 13 g/dL in men. For children ages 1 to 3, the threshold is 11 g/dL.
- Hematocrit: the percentage of your blood volume made up of red blood cells. Low hematocrit tracks closely with low hemoglobin and confirms the finding.
- Mean corpuscular volume (MCV): the average size of your red blood cells. This number helps narrow down the cause. Small red blood cells point toward iron deficiency. Large red blood cells suggest a vitamin B12 or folate problem. Normal-sized red blood cells with low hemoglobin can indicate chronic disease or recent blood loss.
A CBC is fast, inexpensive, and available at virtually any lab. Results typically come back the same day or within 24 hours. If your hemoglobin and hematocrit are normal, anemia is ruled out. If they’re low, the MCV and additional tests guide what happens next.
Iron Studies
Iron deficiency is the most common cause of anemia worldwide, so if your CBC shows low hemoglobin with small red blood cells, your doctor will likely order an iron panel. The most useful number on this panel is ferritin, a protein that reflects how much iron your body has stored.
In adults, a ferritin level below 15 micrograms per liter is diagnostic of iron deficiency. Levels between 15 and 30 are considered probable iron deficiency. Above 30, iron deficiency is unlikely in otherwise healthy people. These cutoffs shift upward in certain situations: for older adults, ferritin needs to be above 50 to confidently rule out deficiency, and for people with chronic inflammatory conditions like inflammatory bowel disease, the threshold rises to 70 or even 100. That’s because inflammation artificially inflates ferritin levels, masking a true deficiency.
When chronic disease is present, a fasting transferrin saturation test helps clarify the picture. A transferrin saturation below 20% in someone with inflammation strongly suggests real iron deficiency, even if ferritin looks normal. For people with chronic kidney disease, the threshold is slightly higher at 24%.
Vitamin B12 and Folate Tests
If your CBC reveals large red blood cells, the next step is checking your vitamin B12 and folate levels. B12 below 150 ng/L is considered definitive evidence of deficiency. Levels between 150 and 400 fall in a gray zone where deficiency is possible but not certain. Folate below 4 mcg/L suggests folate deficiency.
Both deficiencies can cause a type of anemia called megaloblastic anemia, where the bone marrow produces oversized, immature red blood cells that don’t function properly. B12 deficiency can also cause nerve damage, including tingling and numbness in the hands and feet, so catching it matters beyond just the anemia itself.
When results are borderline, a follow-up test measuring two compounds in your blood can distinguish between the two deficiencies. In B12 deficiency, both compounds (homocysteine and methylmalonic acid) are elevated. In folate deficiency, only homocysteine rises while methylmalonic acid stays normal. This distinction matters because the treatments are different.
Checking for Hidden Blood Loss
Iron deficiency anemia in adults, especially men and postmenopausal women, raises a critical question: where is the iron going? One common answer is slow, invisible bleeding in the digestive tract. A fecal occult blood test checks for microscopic amounts of blood in your stool that you wouldn’t see on your own.
A positive result is a strong predictor of gastrointestinal bleeding. In one multicenter study, patients with unexplained iron deficiency anemia who tested positive on a fecal occult blood test were more than five times as likely to have ongoing GI bleeding compared to those who tested negative. Sixty percent of those with positive results had lesions in the lower part of the small intestine. This test is simple (you collect a small stool sample at home) but can prompt important follow-up, including endoscopy to find and treat the source of bleeding.
Reticulocyte Count
If the cause of your anemia isn’t obvious from the basic tests above, your doctor may check your reticulocyte count. Reticulocytes are brand-new red blood cells freshly released from your bone marrow. Their numbers reveal whether your bone marrow is responding appropriately to the anemia or is part of the problem.
A high reticulocyte count (reflected by a reticulocyte production index above 2) means your bone marrow is working overtime to replace lost red blood cells. This pattern fits with anemia caused by bleeding or by red blood cells being destroyed too quickly. A low reticulocyte count (index below 2) means the bone marrow isn’t keeping up, pointing toward conditions where production itself is impaired, such as aplastic anemia or bone marrow disorders.
Screening for Children
The American Academy of Pediatrics recommends that all children be screened for anemia at around 12 months of age with a hemoglobin test. This is the age when iron stores from birth are typically depleted, and dietary iron intake becomes critical. A hemoglobin below 11 g/dL at this age requires further evaluation to determine whether iron deficiency is the cause. Premature infants and babies who were exclusively breastfed without iron supplementation are at higher risk and may need earlier or more frequent testing.
Why Home Test Kits Fall Short
At-home hemoglobin testing devices, which use a finger prick to estimate your hemoglobin level, are widely available online. Their convenience is appealing, but their accuracy is a real problem. Multiple studies comparing finger-prick devices against standard lab blood draws have consistently found significant variability. Capillary blood from a finger prick tends to read about 0.5 g/dL higher than venous blood, which could make you appear less anemic than you are.
The repeatability of these devices is also poor. One analysis of a popular home device found that 31% of results differed from laboratory values by more than 10%. Even with averaging multiple readings, nearly 18% still fell outside that range. Sensitivity for detecting anemia from capillary samples has been measured below 80% in some studies, meaning roughly one in five people with actual anemia would get a falsely reassuring normal result. A standard venous blood draw at a lab remains the only reliable way to check for anemia.