A complete blood count (CBC) is a common laboratory test that provides a detailed look at the cells circulating in the bloodstream, including red cells, white cells, and platelets. The Mean Corpuscular Hemoglobin (MCH) is a specific measurement within the red blood cell indices that provides insight into red cell health. An elevated MCH value indicates that the average amount of hemoglobin carried by each red blood cell is higher than typical. This result signals the need for further investigation to determine the underlying cause.
Understanding Mean Corpuscular Hemoglobin (MCH)
The MCH value quantifies the average mass of hemoglobin contained within a single red blood cell. Hemoglobin is the protein molecule responsible for binding and transporting oxygen from the lungs to the body’s tissues. This measurement is typically expressed in picograms (pg) per cell, with a normal reference range for adults generally falling between 27 and 33 pg/cell, though this can vary by laboratory.
A high MCH is often linked to an increase in the size of the red blood cells, a condition known as macrocytosis. Macrocytic cells are physically larger than normal, allowing them to hold a greater amount of hemoglobin, which elevates the MCH reading. This relationship is confirmed by examining the Mean Corpuscular Volume (MCV), which measures average red blood cell size; when MCH is high, MCV is usually also high.
Primary Nutritional Causes of High MCH
The most common reasons for an elevated MCH are deficiencies in Vitamin B12 and Folate (Vitamin B9). These nutrients are necessary for DNA synthesis, which is required for the continuous production of new red blood cells in the bone marrow. When either vitamin is lacking, red blood cell precursors cannot complete cell division.
This impaired division leads to the formation of abnormally large, immature red blood cells known as megaloblasts, which are released into the circulation as macrocytes. Because hemoglobin production is less affected than cell division, these oversized cells contain a higher total amount of hemoglobin, resulting in the high MCH value. A B12 deficiency often stems from absorption problems, such as Pernicious Anemia, where the body cannot absorb the vitamin from the gut. Folate deficiency is often related to inadequate diet, chronic alcohol use, or medical conditions that increase the body’s demand.
Systemic Conditions That Elevate MCH
Beyond nutritional shortages, several systemic conditions can interfere with red blood cell development and cause an elevated MCH. Chronic, heavy alcohol use is a frequent contributor because alcohol is toxic to the bone marrow, disrupting normal red blood cell maturation. Advanced liver disease is another cause of macrocytosis, as the liver plays a role in lipid metabolism and red blood cell membrane health.
Conditions affecting the thyroid gland, specifically an underactive thyroid (hypothyroidism), can also lead to a high MCH. Thyroid hormones influence cellular metabolism, and their deficiency can slow down bone marrow activity and impair red blood cell formation. Certain medications, including some chemotherapy drugs, antivirals, and anticonvulsants, can disrupt DNA synthesis. This disruption is similar to B vitamin deficiencies, leading to the production of larger red blood cells and subsequent high MCH readings.
Recognizing Symptoms and Next Steps
A high MCH result itself does not usually cause immediate symptoms; rather, symptoms are related to the underlying condition, such as anemia. The macrocytic anemia that often accompanies high MCH typically causes chronic fatigue, generalized weakness, and shortness of breath due to reduced oxygen delivery. A B12 deficiency can also present with neurological symptoms, including numbness, tingling in the hands and feet, or difficulty with balance and memory.
The next step after identifying an elevated MCH is a diagnostic workup to pinpoint the cause. This typically involves further blood tests, including serum levels of Vitamin B12 and Folate, to confirm a nutritional deficiency. A physician may also order liver function tests or thyroid hormone assays to check for systemic causes like liver disease or hypothyroidism. Treatment is tailored to the confirmed cause; B vitamin deficiencies require supplementation, while systemic causes require managing the primary condition, such as adjusting medication or abstaining from alcohol.