What causes a decrease in Mean Corpuscular Volume (MCV) and Mean Corpuscular Hemoglobin (MCH) in a patient?

From the Guidelines

A decrease in Mean Corpuscular Volume (MCV) and Mean Corpuscular Hemoglobin (MCH) typically indicates microcytic hypochromic anemia, most commonly caused by iron deficiency anemia, as evidenced by the European consensus on the diagnosis and management of iron deficiency and anaemia in inflammatory bowel diseases 1. The most common cause of microcytic hypochromic anemia is iron deficiency anemia, where insufficient iron leads to smaller red blood cells with less hemoglobin. Other causes include:

• Thalassemia (a genetic disorder affecting hemoglobin production)
• Anemia of chronic disease
• Sideroblastic anemia
• Lead poisoning Iron deficiency may result from:
• Blood loss (such as gastrointestinal bleeding, heavy menstrual periods)
• Poor dietary intake
• Malabsorption disorders like celiac disease
• Increased iron requirements during pregnancy Treatment depends on the underlying cause but often includes iron supplementation (typically ferrous sulfate 325mg orally three times daily for 3-6 months) for iron deficiency, as suggested by the guidelines for the management of iron deficiency anaemia by the British Society of Gastroenterology 1. Blood transfusions may be necessary in severe cases, and diagnostic workup should include a complete blood count, iron studies (serum iron, ferritin, total iron binding capacity), and potentially hemoglobin electrophoresis to rule out thalassemia, as recommended by the practice guidelines for the diagnosis and management of microcytic anemias due to genetic disorders of iron metabolism or heme synthesis 1. These values decrease because without adequate iron or proper hemoglobin synthesis, red blood cells cannot develop to their normal size and hemoglobin content. The European consensus on the diagnosis and management of iron deficiency and anaemia in inflammatory bowel diseases also highlights the importance of considering the percentage of anaemia of chronic disease and the role of reticulocyte count in the diagnostic workup 1.

From the Research

Causes of Decreased MCV and MCH

• Decreased MCV (Mean Corpuscular Volume) and MCH (Mean Corpuscular Hemoglobin) values are commonly seen in microcytic anemias, which are characterized by small, often hypochromic, red blood cells 2, 3, 4, 5, 6.
• The most common cause of microcytic anemia is iron deficiency anemia (IDA), which is defined as a decrease in iron stores, leading to a reduction in hemoglobin synthesis and subsequently, a decrease in MCV and MCH values 2, 3, 4, 5.
• Other causes of microcytic anemia include thalassemia, anemia of chronic disease, and sideroblastic anemia, which can also lead to decreased MCV and MCH values 2, 3, 4, 5, 6.

Diagnostic Considerations

• The diagnosis of microcytic anemia is based on laboratory tests, including complete blood count (CBC), serum iron, total iron binding capacity, transferrin saturation, and serum ferritin 2, 3, 4, 5.
• The measurement of serum ferritin is a reliable test for diagnosing iron deficiency anemia, and a low value is indicative of depleted iron stores 2, 3, 4, 5.
• The microcytic to hypochromic RBC ratio has been proposed as a useful index for distinguishing between thalassemia and iron deficiency anemia, with a ratio >6.4 being indicative of thalassemia 6.

Clinical Implications

• Decreased MCV and MCH values can have significant clinical implications, including fatigue, weakness, and shortness of breath, and require prompt diagnosis and treatment 2, 3, 4, 5, 6.
• The treatment of microcytic anemia depends on the underlying cause, with iron supplementation being the primary treatment for iron deficiency anemia, and other treatments, such as erythropoietin and red blood cell transfusions, being used for other causes of microcytic anemia 2, 3, 4, 5.