Mean Corpuscular Hemoglobin (MCH) And ... - Medscape Reference

Description

MCH is the content (weight) of Hb of the average red cell, [5] 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, i.e., Hb (below), and red blood cell count as follows [5] :

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

A related value is MCHC, which is the average concentration of Hb in a given volume of packed red blood cells, [5] or, in other words, the ratio of Hb mass to the volume of red cells. [1] It is also not measured directly but is calculated from the Hb concentration, i.e., Hb (below), and the hematocrit (Hct):

• MCHC = Hb (in g/dL)/Hct (%)

Indications/Applications

As part of a standard CBC, MCH and MCHC can be used for evaluating anemia and monitoring its response to treatment, along with the MCV values (see Interpretation). [6]

Considerations

MCH and MCHC, as well as 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 a peripheral blood smear review can help confirm the above findings. [1, 4, 7, 8] A peripheral smear can also reveal the presence of nucleated RBCs, sickle cells, spherocytes, acanthocytes, RBC agglutinates, fragments/schistocytes (including microspherocytes), Hb C crystals, cryoprotein precipitates and/or crystals, fat globules, and fibrin strands. [10] 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 (> 2000 mg/dL) [9] that results in plasma turbidity will spuriously increase Hb, hence falsely elevating MCH. [1]

MCHC, as measured by a multichannel analyzer (instrument used nowadays for CBC), is a stable variable. Therefore, it plays a key role in laboratory quality control. [1, 2]

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 hyperlipidemia due to spuriously high Hb.

Other factors influencing MCH and MCHC values are as follows:

• Improper sample collection, storage, and transport conditions may cause in vitro hemolysis, leading to a falsely low RBC count and hematocrit values, resulting in artifactually high MCH and MCHC levels. [10]
• Bilirubin levels greater than 25-35 mg/dL (425-600 µmol/L) may cause spectral interference in Hb assays, leading to falsely elevated Hb, MCH, and MCHC values. [10]
• Cold-reactive immunoglobulin (Ig)M antibodies (reactive at temperatures < 37° C) — seen in those with cold agglutinin disease or paraproteinemia, cytomegalovirus infection, or mycoplasma pneumonia — can cause RBC autoagglutination (clumping), leading to falsely elevated MCH and MCHC. [10]
• Elevated levels of paraproteins (IgM, IgG, and IgA) in plasma cell and lymphoplasmacytic disorders, lysis-resistant abnormal RBCs (containing HB C or HB S), and very high WBC counts ≥ 100,000/μL (hyperleukocytosis) tend to interfere with Hb estimation, causing falsely higher Hb, MCH, and MCHC. [10]

Blood glucose concentrations ≥ 600 mg/dL (≥ 33 mmol/L) may cause falsely lower MCHC. [10] Visual inspection of a centrifuged or gravity-settled blood specimen can help in detecting hemolytic discoloration, hyperbilirubinemia-induced icterus (bright yellow), a milky turbid appearance characteristic of blood lipemia, RBC clumps, and cryoprotein precipitates. [10]

Understanding Mean Corpuscular Hemoglobin and Mean Corpuscular Hemoglobin Concentration 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 hematological 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 anemias can be thought of with this analogy.

A simplified illustration of different types of anemia. (1a) Normochromic normocytic anemia: Normal mean corpuscular volume (MCV) (normal red blood cell [RBC] size = normal tube size), normal mean corpuscular hemoglobin (MCH) (normal hemoglobin in each RBC = normal amount of air in each river tube), normal mean corpuscular hemoglobin concentration (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). View Media Gallery Normal mean corpuscular hemoglobin (MCH) and elevated mean corpuscular hemoglobin concentration (MCHC) in hereditary spherocytosis (ball-shaped red blood cells [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. View Media Gallery