The Complete Blood Count (CBC) is a routine laboratory test that provides a detailed snapshot of the cells circulating in the blood, including white blood cells, platelets, and red blood cells. To assess the health and oxygen-carrying capacity of red blood cells, doctors rely on calculated values known as red cell indices. Among these indices, MCH and MCHC offer distinct details about the hemoglobin content within these cells.
Defining MCH and MCHC
MCH stands for Mean Corpuscular Hemoglobin. It measures the average mass or weight of hemoglobin contained within a single red blood cell. Hemoglobin is the iron-containing protein that enables red cells to transport oxygen. The MCH value is typically expressed in picograms (pg) per cell, with a normal reference range for adults between 27 and 33 pg/cell.
MCHC, or Mean Corpuscular Hemoglobin Concentration, assesses the average concentration of hemoglobin relative to the volume of the red blood cell. While MCH measures the amount of hemoglobin, MCHC describes the density or saturation of hemoglobin within the cell’s total space. This value is usually reported in grams per deciliter (g/dL), with an adult normal range commonly set between 32 and 36 g/dL.
Interpreting High and Low MCH Levels
The MCH measurement is strongly influenced by the size of the red blood cell, which is separately quantified by the Mean Corpuscular Volume (MCV). Since MCH reflects the absolute amount of hemoglobin, a change in cell size often results in a proportional change in the MCH value. A high MCH suggests that the red blood cells are larger than normal, a condition known as macrocytosis.
Elevated MCH values are frequently associated with macrocytic anemias, where the body produces abnormally large red cells containing a greater mass of hemoglobin. This is commonly seen in deficiencies of Vitamin B12 or folate, which are necessary for proper cell division. Other factors, such as long-term alcohol use disorder or certain thyroid problems, can also lead to an elevated MCH.
Conversely, a low MCH suggests that the red blood cells contain less than the average mass of hemoglobin. This finding often corresponds with microcytic anemias, where the red cells are physically smaller than usual. The most frequent cause of a low MCH is iron deficiency anemia, since iron is necessary for hemoglobin production. Thalassemia, inherited blood disorders that impair hemoglobin synthesis, can also result in a low MCH.
Interpreting High and Low MCHC Levels
MCHC provides insight into the intensity of the red cell’s color, or its hemoglobin saturation, independent of cell size. A low MCHC is termed hypochromia and is a reliable indicator of reduced hemoglobin saturation. This suggests that the red cells are pale because they are not fully saturated with hemoglobin.
Hypochromia is characteristic of conditions where hemoglobin production is impaired, such as iron deficiency anemia and thalassemia. In these cases, the concentration of hemoglobin inside the cell is below the normal threshold. Less common causes of low MCHC include lead poisoning, which interferes with the enzymes needed to synthesize hemoglobin.
An elevated MCHC is referred to as hyperchromia, though true hyperchromia is rare because a red blood cell cannot be “over-saturated” with hemoglobin. When MCHC is genuinely high, it often indicates a structural issue where the red cell is shrunken or spherical, concentrating the hemoglobin into a smaller volume. Conditions like hereditary spherocytosis, a genetic disorder causing abnormally shaped red cells, or severe burns that lead to cell dehydration, can cause this result. A high MCHC can sometimes be a laboratory artifact caused by issues like red cell clumping (agglutination) or high fat levels (lipemia) in the blood sample.
The Role of MCH and MCHC in Diagnosing Anemia
MCH and MCHC are instrumental in helping healthcare providers classify the specific type of anemia present in a patient. Anemia is defined by low levels of hemoglobin, but its causes are diverse and require targeted treatment. By comparing MCH and MCHC values alongside other indices, a pattern emerges that points toward the underlying problem.
For example, if both MCH and MCHC are low, it suggests a microcytic, hypochromic anemia, directing investigation toward iron deficiency or thalassemia. Conversely, if MCH is high while MCHC remains normal, it points toward a macrocytic anemia, prompting testing for B12 or folate deficiency. These indices serve as diagnostic tools, providing a framework for further blood tests, and should always be interpreted by a healthcare professional within the context of a patient’s medical history.