Mean Corpuscular Hemoglobin (MCH) and Mean Corpuscular Hemoglobin Concentration (MCHC)

The reference ranges for mean corpuscular hemoglobin (MCH) are as follows ^[1] :

• Adult/elderly/child: 27-31 pg
• Newborn: 32-34 pg

The reference ranges for mean corpuscular hemoglobin concentration (MCHC) are as follows ^[1] :

• Adult/elderly/child: 32-36 g/dL (or 32-36%)
• Newborn: 32-33 g/dL (or 32-33%)

Both mean corpuscular hemoglobin (MCH) and mean corpuscular hemoglobin concentration (MCHC) reflect the average hemoglobin content of red blood cells in slightly different ways (see "Description" in Background). Although MCH expresses the average content (mass, weight) of hemoglobin per red cell, MCHC expresses the average weight of hemoglobin per unit volume of red cell (see also "Understanding MCH and MCHC Using a River Tubing Analogy" in Background). ^[2]

MCH, MCHC, and MCV are parts of red cell indices (parameters reflecting size and hemoglobin content of red cells) that have traditionally been used to aid in the differential diagnosis of anemia. ^[3] Although MCH can be used to determine if an anemia is hypo-, normo-, or hyperchromic, the mean corpuscular volume (MCV) has to be considered along with the MCH since cell volume (MCV) affects the content of hemoglobin present per cell (MCH), and MCH can decrease or increase in parallel to the MCV. ^[3] Thus, MCHC in the past has been thought to be a better parameter than MCH to determine hypochromasia. ^[4]

However, the MCHC, as measured by a multichannel analyzer nowadays, is not affected by plasma trapping, which typically results in slightly increased hematocrit. MCHC is not then decreased when there is hypochromasia. Therefore, MCV together with red cell distribution width (RDW) have become the two most useful parameters in classifying anemias, while MCH and MCHC do not add significant, clinically relevant information. ^{[3, 5]} MCH and MCHC, nonetheless, play an important role in laboratory quality control. ^{[2, 3]} These parameters allow laboratories to detect potential causes of erroneous results, such as hyperlipidemia or hemolysis (both in vivo and in vitro), so the correct results can be reported.

MCHC, when increased, can be useful clinically as an indicator of increased spherocytes (spherocytosis), as in hereditary spherocytosis or autoimmune hemolytic anemia. It is also increased in homozygous sickle cell or hemoglobin C disease. ^[2]

Specimen: Whole blood, usually collected by venipuncture

Collection: EDTA tube (purple/lavender top; see image below) containing EDTA potassium salt additive as an anticoagulant

Whole blood tube with lavender closure and EDTA potassium salt additive.

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Panels: Complete blood count (CBC)

Description

MCH is the content (weight) of hemoglobin (Hb) of the average red cell, ^[6] or, in other words, a reflection of hemoglobin mass in red cells. It is not measured directly but is calculated from the measured Hb concentration (Hb) and red blood cell count (RBC) as follows ^[6] :

• MCH = Hb (in g/L)/RBC (in millions/µL) or

• MCH = [Hb (in g/dL)/RBC (in millions/µL)] x 10

A related value is mean corpuscular hemoglobin concentration (MCHC), which is the average concentration of hemoglobin in a given volume of packed red blood cells, ^[6] or in other words, the ratio of hemoglobin mass to the volume of red cells. ^[2] It is also not measured directly but is calculated from the Hb concentration (Hb) and the hematocrit (Hct):

• MCHC = Hb (in g/dL)/Hct (%)

Indications/Applications

As part of a standard CBC, the MCH and MCHC can be used for the evaluation of anemia along with the MCV (see Interpretation). ^[7]

Considerations

MCH and MCHC, as well as the MCV, reflect average values and may not adequately reflect RBC changes when mixed RBC populations are present, such as dimorphic RBC populations in sideroblastic anemia or combined iron deficiency anemia (decreased MCV and MCH) and megaloblastic anemia (increased MCV and MCH). An elevated RDW will provide a clue for heterogenous red cell size (anisocytosis) and/or the presence of two red cell populations, and peripheral blood smear review can help confirm the above findings. ^{[2, 5, 8, 9]}

MCH can be spuriously increased or decreased when an accurate measurement of Hb concentration and red blood cell count is disturbed, as MCH calculation is derived from these two parameters. For example, hyperlipidemia resulting in plasma turbidity will spuriously increase Hb, hence falsely elevate MCH. ^[2]

MCHC, as measured by a multichannel analyzer (instrument used nowadays for complete blood count [CBC]), is a stable variable. Therefore, it plays an important role in laboratory quality control. ^{[2, 3]} MCHC is spuriously decreased or increased when an accurate measurement of Hb and hematocrit is disturbed, as the MCHC calculation is derived from these two parameters. For example, it can be spuriously increased in autoagglutination and hyperlipidemia due to spuriously low hematocrit and spuriously high Hb, respectively. Truly increased MCHC usually occurs in hereditary spherocytosis (see the second image, below) or in some cases of homozygous sickle cell or hemoglobin C disease. ^[2]

Understanding MCH and MCHC Using a River Tubing Analogy

To help understand RBC indices, imagine a river tubing scenario. Each RBC is a river tube (doughnut-shaped tube). Many river tubes are in the river, just like many RBCs are in our circulation (a “river of life”). The following hematologic values are then analogous:

• RBC count = the number of river tubes per unit volume of river water

• Hb concentration = the content (weight) of air in the river tubes per unit volume of river water

• Hematocrit = the volume of river tubes per unit volume of river water

• MCV = average river tube size (volume)

• MCH = average content (weight) of air in each river tube

• MCHC = average density of air in each river tube, or average river tube inflation

Certain pathologic conditions such as anemia are associated with a low RBC count (too few river tubes in the river). The images below demonstrate how different types of anemia can be thought of with this analogy.

Simplified illustration of different types of anemia. 1a) Normochromic normocytic anemia: normal MCV (normal RBC size = normal tube size), normal MCH (normal hemoglobin in each RBC = normal amount of air in each river tube), normal MCHC (normal average concentration of hemoglobin in a given volume of packed RBCs = normal density of air, i.e., normal inflation); 1b) Microcytic hypochromic anemia: low MCV (small RBC size = small tube size), low MCH (less hemoglobin in each RBC = less air in each river tube), low MCHC (low average concentration of hemoglobin in a given volume of packed RBC = low density of air, i.e., underinflation); 1c) Macrocytic normochromic anemia: high MCV (large RBC size = large tube size), high MCH (more hemoglobin in each RBC = more air in each river tube), normal MCHC (normal average concentration of hemoglobin in a given volume of packed RBC = normal density of air, i.e., normal inflation).

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Normal MCH and elevated MCHC in hereditary spherocytosis (ball-shaped RBCs): Imagine the river tubes were bitten by alligators (loss of surface) and reconstructed into balls with the same amount of air (normal MCH); therefore, the balls will be overinflated (high MCHC) due to the reduced surface/volume ratio.

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