Anemia is diagnosed when a person has a lower than normal level of red blood cells or hemoglobin, the protein responsible for carrying oxygen throughout the body. Microcytic anemia is a specific classification where red blood cells are smaller than typical (microcytosis). While an association with certain cancers exists, it is not the most frequent cause, and a methodical evaluation is the appropriate response.
Understanding Microcytic Anemia
Microcytic anemia is defined by the Mean Corpuscular Volume (MCV) measurement on a complete blood count (CBC) test, which calculates the average size of red blood cells. A value below 80 femtoliters (fL) in adults indicates microcytosis, meaning the red blood cells are abnormally small.
The small size results from insufficient hemoglobin, making the cells paler than normal (hypochromia). The Mean Corpuscular Hemoglobin (MCH) measures the average mass of hemoglobin in each cell and is usually low. Therefore, the condition is often referred to as microcytic, hypochromic anemia, reflecting both the small size and pale appearance.
Common Non-Malignant Causes
The most frequent reason for microcytic anemia is Iron Deficiency Anemia (IDA), accounting for the majority of cases. Iron is required to produce hemoglobin, so a lack of it leads to the creation of smaller cells with less oxygen-carrying capacity. IDA often results from chronic, non-malignant blood loss, such as heavy menstrual bleeding or slow bleeding from gastrointestinal issues like ulcers or hemorrhoids.
Dietary factors, poor absorption (due to conditions like celiac disease), or increased iron demand (such as during pregnancy) can also cause IDA. Laboratory results typically show a very low serum ferritin level, a marker for the body’s iron stores, confirming the diagnosis.
Another common cause, especially in certain ethnic groups, is Thalassemia, a group of inherited genetic blood disorders. This condition involves defects in the production of globin chains that form hemoglobin, leading to microcytosis even when iron stores are normal. Thalassemia is a lifelong condition, unlike iron deficiency.
Anemia of Chronic Disease (ACD) can also present with microcytic red blood cells, though it is often normocytic. ACD is linked to long-term inflammatory states, such as autoimmune diseases or chronic kidney disease. Inflammation causes the body to improperly manage iron, trapping it within storage cells and preventing its use in making new red blood cells.
When Microcytic Anemia Signals Malignancy
While less common than non-malignant causes, microcytic anemia can indicate an underlying malignancy. The primary mechanism linking cancer to this anemia is chronic, occult blood loss (slow, hidden bleeding). This slow loss depletes the body’s iron stores over time, leading directly to microcytic Iron Deficiency Anemia.
Cancers of the gastrointestinal tract, particularly colorectal cancer, are the most relevant examples, as a tumor can bleed internally without causing noticeable symptoms. The resulting iron deficiency anemia is often one of the first detectable signs of these solid tumors. Other malignancies can cause microcytosis by triggering severe Anemia of Chronic Disease (ACD).
Cancers like lymphoma or multiple myeloma can cause systemic inflammation or infiltrate the bone marrow, disrupting the production of healthy red blood cells. In these cases, microcytosis is a secondary symptom resulting from the cancer’s effect on the blood-forming process or iron utilization.
Next Steps in Diagnosis and Evaluation
The medical workup focuses on accurately determining the cause to guide effective treatment. This involves a series of blood tests, including a full iron panel that measures serum iron, total iron-binding capacity, and ferritin levels. Low ferritin strongly suggests iron deficiency, while normal or elevated ferritin suggests other causes like thalassemia or ACD.
If iron studies are inconclusive or point toward a genetic cause, hemoglobin electrophoresis is performed to check for abnormal hemoglobin types and diagnose thalassemia. If iron deficiency is confirmed in an adult, especially a male or a postmenopausal female, the search immediately turns to finding the source of blood loss.
This search often involves procedures like an upper endoscopy or a colonoscopy to visualize the gastrointestinal tract and detect ulcers, polyps, or tumors that may be bleeding. Prompt consultation with a physician is necessary to navigate this diagnostic sequence and ensure any serious underlying condition is identified and treated quickly.