The Mean Corpuscular Hemoglobin (MCH) is a numerical value reported as part of a standard Complete Blood Count (CBC) test. This measurement provides a direct insight into the quality of your red blood cells, specifically focusing on the oxygen-carrying protein they contain. It serves as one of the red blood cell indices that healthcare providers use to evaluate blood health and diagnose various conditions, particularly different forms of anemia.
Defining Mean Corpuscular Hemoglobin
Mean Corpuscular Hemoglobin is the measure of the average weight of hemoglobin present within a single red blood cell. Hemoglobin is a complex protein molecule rich in iron that is responsible for binding to and transporting oxygen from the lungs to the body’s tissues. The MCH value quantifies the absolute amount of this oxygen-carrying protein in each cell.
This value is not directly measured by laboratory equipment but is instead calculated using other data collected during the CBC. The formula divides the total mass of hemoglobin in a given volume of blood by the total number of red blood cells in that same volume. The standard unit of measurement for MCH is picograms (pg).
For most adults, the typical reference range for MCH falls between approximately 27 and 33 picograms per cell. MCH is closely related to the size of the red blood cell, meaning a smaller cell generally contains less hemoglobin by weight.
What Low MCH Values Indicate
A low MCH value is usually associated with red blood cells that are both smaller than average (microcytic) and paler than normal (hypochromic). The most frequent reason for this condition is insufficient production of hemoglobin, which leads to the cells becoming deficient in the protein.
The most common cause of low MCH is iron deficiency anemia. Iron is an essential component required for the body to synthesize hemoglobin, and a lack of it prevents the red blood cells from being properly filled. This deficiency can arise from insufficient dietary intake, poor absorption, or chronic blood loss from sources like heavy menstrual bleeding or gastrointestinal ulcers.
Conditions that also lead to a low MCH result include inherited blood disorders like thalassemia, where the body produces abnormal or reduced amounts of hemoglobin. Anemia of chronic disease, which occurs with long-term infections or inflammatory conditions, can also impair the body’s ability to utilize iron effectively. The combination of a low MCH with a low mean corpuscular volume (MCV) strongly suggests a microcytic anemia.
What High MCH Values Indicate
A high MCH value indicates that the average red blood cell contains a greater than normal amount of hemoglobin by weight. This elevation typically correlates with macrocytic red blood cells, meaning the cells are larger than average. These larger cells, while containing more hemoglobin individually, are often immature and less effective at oxygen delivery.
The primary causes for an elevated MCH are nutritional deficiencies, specifically a lack of Vitamin B12 or folate (Vitamin B9). Both of these B vitamins are necessary for proper DNA synthesis within the bone marrow. When they are deficient, the red blood cell precursors cannot divide normally, leading to the release of oversized, poorly formed cells into the bloodstream. This condition is known as megaloblastic anemia.
Chronic conditions such as liver disease and excessive alcohol consumption are known causes of macrocytosis. These conditions can directly affect the health of the red blood cell membrane or interfere with the metabolism of B vitamins. Hypothyroidism can also sometimes be associated with high MCH readings.