Mean corpuscular hemoglobin concentration

The mean corpuscular hemoglobin concentration (MCHC) is a measure of the concentration of haemoglobin in a given volume of packed red blood cell.

Not to be confused with mean corpuscular hemoglobin per erythrocyte, although they are predictably correlated in healthy states.
Hemoglobin

It is calculated by dividing the haemoglobin by the haematocrit. Reference ranges for blood tests are 32 to 36 g/dL (320 to 360g/L),[1] or between 4.81 and 5.58 mmol/L. It is thus a mass or molar concentration. Still, many instances measure MCHC in percentage (%), as if it were a mass fraction (mHb / mRBC).[2][3] Numerically, however, the MCHC in g/dL and the mass fraction of haemoglobin in red blood cells in % are identical, assuming an RBC density of 1g/mL and negligible haemoglobin in plasma.

Interpretation

A low MCHC can be interpreted as identifying decreased production of hemoglobin. MCHC can be normal even when hemoglobin production is decreased (such as in iron deficiency) due to a calculation artifact. MCHC can be elevated ("polychromatic") in hereditary spherocytosis, sickle cell disease and homozygous haemoglobin C disease, depending upon the hemocytometer.[4][5] MCHC can be elevated in some megaloblastic anemias. MCHC can be falsely elevated when there is agglutination of red cells (falsely lowering the measured RBC) or when there is opacifaction of the plasma (falsely increasing the measured hemoglobin). Causes of plasma opacification that can falsely increase the MCHC include hyperbilirubinemia, hypertryglyceridemia, and free hemoglobin in the plasma (due to hemolysis).

Complicating conditions

Because of the way automated analysers count blood cells, a very high MCHC (greater than about 370 g/L) may indicate the blood is from someone with a cold agglutinin, or there may be some other problem resulting in one or more artifactual results affecting the MCHC.

For example, for some patients with cold agglutinins, when their blood gets colder than 37 °C, the red cells will clump together. As a result, the analyzer may incorrectly report a low number of very dense red blood cells. This will result in an impossibly high number when the analyzer calculates the MCHC. This problem is usually picked up by the laboratory before the result is reported. The blood can be warmed until the cells separate from each other, and quickly put through the machine while still warm.

There are four steps to perform when a suspect increased MCHC (>370 g/L or >37.0 g/dL) is received from the analyzer:

  1. Remix the EDTA tube—if the MCHC corrects, report corrected results
  2. Incubation at 37 °C—if the MCHC corrects, report corrected results and comment on possible cold agglutinin
  3. Saline replacement: Replace plasma with same amount of saline to exclude interference e.g. Lipemia and Auto-immune antibodies—if the MCHC corrects, report corrected results and comment on Lipemia
  4. Check the slide for spherocytosis (e.g. in hereditary spherocytosis, among other causes)

Worked example
Measure Units Conventional units Conversion
Hct 40%
Hb 100 grams/liter 10 grams/deciliter (deci- is 10−1)
RBC 5E+12 cells/liter 5E+6 cells/μL (micro is 10−6)
MCV = (Hct/100) / RBC 8E-14 liters/cell 80 femtoliters/cell (femto- is 10−15)
MCH = Hb / RBC 2E-11 grams/cell 20 picograms/cell (pico- is 10−12)
MCHC = Hb / (Hct/100) 250 grams/liter 25 grams/deciliter (deci is 10−1)

See also

References
  1. MedlinePlus Encyclopedia RBC indices
  2. Blood Test Results - Normal Ranges Bloodbook.Com. Retrieved on Jan 7, 2009
  3. MedicineNet > Definition of MCHC Last Editorial Review: 7/21/1999
  4. Hill, Valerie L.; Simpson, Virginia Z.; Higgins, Jeanette M.; Hu, Zonghui; Stevens, Randy A.; Metcalf, Julie A.; Baseler, Michael (2017-01-28). "Evaluation of the Performance of the Sysmex XT-2000i Hematology Analyzer With Whole Bloods Stored at Room Temperature". Laboratory Medicine. 40 (12): 709–718. doi:10.1309/T0FJYP2RBXEHX4. ISSN 0007-5027. PMC 2860627. PMID 20431699.
  5. Rifkind, David; Cohen, Alan S. (2002). The Pediatric Abacus. Informa Healthcare. p. 54. ISBN 978-1-84214-147-2.
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