Mean corpuscular hemoglobin concentration

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

The mean corpuscular hemoglobin concentration, a measure of the concentration of hemoglobin in a given volume of packed red blood cells. It is reported as part of a standard complete blood count.

It is calculated by dividing the hemoglobin by the hematocrit. Reference ranges for blood tests are 32 to 36 g/dL,[1] or between 19.9 [2] and 22.3[2] mmol/L. It is thus a mass or molar concentration. Still, many instances[3][4] measure MCHC in percentage (%), as if it were a mass fraction (mHb / mRBC). Numerically, however, the MCHC in g/dL and the mass fraction of hemoglobin in red blood cells in % are identical, assuming a RBC density of 1g/mL and negligible hemoglobin in plasma.

Interpretation

MCHC is diminished ("hypochromic") in microcytic anemias, and normal ("normochromic") in macrocytic anemias (due to larger cell size, though the hemoglobin amount or MCH is high, the concentration remains normal). MCHC is elevated ("hyperchromic") in hereditary spherocytosis, sickle cell disease and homozygous hemoglobin C disease.[5]

This count is used to give a rough guide to what shade of red erythrocytes will be (i.e., the paler the color the lower the MCHC will be than the standard).

Complications with cold agglutinin

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. This means that when their blood gets colder than 37°C it starts to clump together. As a result, the analyzer may incorrectly report a low number of very dense red blood cells for blood samples in which agglutination has occurred.

This problem is usually picked up by the laboratory before the result is reported. The blood is warmed until the cells separate from each other, and quickly put through the machine while still warm. This is the most sensitive test for iron deficiency anemia.

There are four steps to perform when an increase 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 / 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 = MCH / MCV 250 grams/liter 25 grams/deciliter (deci is 10−1)

See also

References

  1. ↑ MedlinePlus Encyclopedia RBC indices
  2. 1 2 Converted with conversion factor from (Wallach, Jacques Burton (2007). Interpretation of Diagnostic Tests. Lippincott Williams & Wilkins.). 1 g/dL = 0.6206 mmol/L
  3. ↑ Blood Test Results - Normal Ranges Bloodbook.Com. Retrieved on Jan 7, 2009
  4. ↑ MedicineNet > Definition of MCHC Last Editorial Review: 7/21/1999
  5. ↑ Rifkind, David; Cohen, Alan S. (2002). The Pediatric Abacus. Informa Healthcare. p. 54. ISBN 1-84214-147-3.

External links

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