A Complete Blood Count (CBC) is a common laboratory test that provides a detailed picture of the cells circulating in the blood. This comprehensive panel includes several red blood cell indices, which assess the health and characteristics of oxygen-carrying cells. Mean Corpuscular Hemoglobin (MCH) is one measurement that provides information about the average hemoglobin content within a single red blood cell.
Defining Mean Corpuscular Hemoglobin (MCH)
Mean Corpuscular Hemoglobin (MCH) quantifies the average weight of hemoglobin found inside each red blood cell in a given blood sample. Hemoglobin is the iron-containing protein responsible for binding and transporting oxygen from the lungs to the body’s tissues. The MCH value is a direct reflection of how much of this protein each red cell contains.
The MCH is not measured directly but is mathematically calculated by dividing the total mass of hemoglobin in a volume of blood by the number of red blood cells in that same volume. This calculation yields a value representing the average amount of hemoglobin carried by an individual cell. The standard unit of measurement is the picogram, abbreviated as “pg”.
One picogram is equivalent to one-trillionth of a gram. A typical MCH value indicates the mass of hemoglobin per cell, and this mass is heavily dependent on the cell’s size and its ability to synthesize hemoglobin effectively. The MCH is an indicator of the functional capacity of the red blood cells to deliver oxygen.
Interpreting MCH Values
The interpretation of MCH begins with establishing a normal reference range, which typically falls between 27 and 33 picograms (pg) per cell for adults. These ranges can vary slightly between different laboratories based on the equipment and specific testing methods used. An MCH result within this established range suggests that the red blood cells contain an adequate amount of hemoglobin.
When MCH results fall outside of this reference range, they are categorized using specific clinical terminology. A low MCH value, generally defined as below 27 pg, indicates that the red blood cells contain less hemoglobin than normal. This finding is often associated with hypochromia, meaning the cells appear paler than usual when viewed under a microscope.
A high MCH value, typically above 33 pg, suggests that the red blood cells are carrying a greater than average amount of hemoglobin. This elevation often occurs when the red blood cells are abnormally large, a condition known as macrocytosis. Although the term “hyperchromic” is sometimes used, it is technically inaccurate because red blood cells simply get larger to accommodate more hemoglobin, rather than becoming darker than normal.
Underlying Causes of Abnormal MCH
Low MCH levels most commonly point toward iron deficiency anemia, resulting from insufficient iron needed for hemoglobin production. Without adequate iron, the body cannot synthesize enough hemoglobin, leading to red blood cells that are smaller and paler. This lack of iron can stem from dietary inadequacy, chronic blood loss, or issues with nutrient absorption.
Another significant cause of low MCH is thalassemia, an inherited blood disorder that directly impairs the body’s ability to produce normal hemoglobin. The genetic defect results in a reduced rate of hemoglobin synthesis, causing the red blood cells to be small and contain a low amount of the oxygen-carrying protein. Chronic inflammatory conditions or long-term infections can also contribute to a low MCH, as inflammation interferes with iron utilization.
Conversely, an elevated MCH is most frequently linked to a deficiency in Vitamin B12 or folate, both necessary for proper red blood cell formation. When these B vitamins are deficient, the bone marrow produces abnormally large red blood cells, called megaloblasts, leading to macrocytic anemia. These larger cells contain a higher overall weight of hemoglobin, resulting in the high MCH reading.
Other factors can also contribute to a high MCH value, including chronic liver disease and excessive alcohol consumption. Certain medications and conditions affecting the thyroid gland, such as hypothyroidism, may also be associated with an increase in the MCH value. In all cases of abnormal MCH, the result prompts further investigation into the underlying nutritional or medical cause.