Anemia is the most common blood disorder worldwide. It develops when your body does not have enough healthy red blood cells or when your red blood cells do not function properly, resulting in reduced oxygen delivery to your tissues and organs. Anemia is diagnosed when hemoglobin levels fall below 13.5 g/dL in men or 12.0 g/dL in women.
The symptoms of anemia reflect reduced oxygen supply to your body. Common symptoms include weakness, fatigue, shortness of breath, dizziness, headaches, irregular or pounding heartbeat, cold hands and feet, pale or yellowish skin, and chest discomfort. The severity of symptoms generally correlates with the degree of anemia, though some patients with chronic, slowly developing anemia may have surprisingly few symptoms despite very low hemoglobin levels.
Iron-deficiency anemia is the most prevalent form globally. It typically results from blood loss (heavy menstrual periods, gastrointestinal bleeding), poor dietary iron intake, or impaired iron absorption. Treatment involves identifying and addressing the underlying cause, along with iron supplementation through diet or oral/intravenous iron. Persistent iron-deficiency anemia always warrants investigation for a source of blood loss.
Vitamin-deficiency anemia results from insufficient vitamin B12 or folate — both essential for red blood cell production. Dietary deficiency is common, but pernicious anemia — an autoimmune condition where the body cannot absorb B12 from the gastrointestinal tract — is an important cause that requires lifelong B12 injections. B12 and folate deficiency produce characteristically large red blood cells (macrocytic anemia), which can be detected on a routine CBC.
Hemolytic anemias occur when red blood cells are destroyed faster than the bone marrow can replace them. Causes include autoimmune disorders (where the immune system attacks its own red cells), inherited conditions like thalassemia and sickle cell disease, mechanical damage from artificial heart valves, infections, and certain medications. Sickle cell anemia is a specific inherited hemolytic anemia where abnormal hemoglobin causes red blood cells to become rigid and sickle-shaped, obstructing small blood vessels and causing pain crises.
Aplastic anemia is a rare but serious condition where the bone marrow fails to produce sufficient blood cells of all types — red cells, white cells, and platelets. It is most commonly caused by the immune system attacking bone marrow stem cells. Aplastic anemia can be life-threatening and may require immunosuppressive therapy or bone marrow transplantation.
Anemia can also develop secondary to chronic diseases such as kidney disease, cancer, rheumatoid arthritis, and inflammatory bowel disease. Chronic kidney disease reduces production of erythropoietin — the hormone that stimulates red blood cell production. Cancer and chemotherapy can suppress bone marrow function directly. These secondary anemias require treating the underlying condition alongside managing the anemia itself.
When should you see a hematologist? Most cases of mild iron-deficiency anemia can be managed by your primary care doctor. However, you should seek specialist evaluation if your anemia does not respond to iron supplementation, if the cause is unclear, if you have abnormal cells on your blood smear, if multiple blood cell lines are affected (not just red cells), or if there is suspicion of a bone marrow disorder. A hematologist can perform specialized testing including bone marrow evaluation to determine the precise cause and guide appropriate treatment.