Mean corpuscular hemoglobin concentration
The Mean corpuscular hemoglobin concentration, a measure of the concentration of haemoglobin 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 haemoglobin by the haematocrit. 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 haemoglobin in red blood cells in % are identical, assuming a RBC density of 1g/mL and negligible haemoglobin in plasma.
Interpretation
MCHC is diminished ("hypochromic") in microcytic anaemias, and normal ("normochromic") in macrocytic anaemias (due to larger cell size, though the haemoglobin amount or MCH is high, the concentration remains normal). MCHC is elevated ("polychromatic")(Hyperchromia is not a correct term) in hereditary spherocytosis, sickle cell disease and homozygous haemoglobin 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 anaemia.
There are four steps to perform when an increase MCHC(>370 g/L or 37.0 g/dL) is received from the analyzer:
- Remix the EDTA tube—if the MCHC corrects, report corrected results
- Incubation at 37 °C—if the MCHC corrects, report corrected results and comment on possible cold agglutinin
- 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
- Check the slide for spherocytosis (e.g. in hereditary spherocytosis, among other causes)
Auto-agglutination: Falsely ↓RBC and ↑MCV Lipaemia: Falsely ↑haemoglobin. Haemolysis: Will falsely increase the MCHC (measured haemoglobin is proportionally higher than HCT or PCV) and falsely decrease the calculated haemoglobin (fewer intact RBC)
Other: Heinz bodies (many, particularly if large) may falsely increase the MCHC but not the MCH. Agglutination: Falsely increases the MCHC (measured haemoglobin is proportionally higher than HCT). The MCH is more accurate in this setting. Excess EDTA: Dehydrates RBC, falsely increasing MCHC and MCH.
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
- ↑ MedlinePlus Encyclopedia RBC indices
- 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
- ↑ Blood Test Results - Normal Ranges Bloodbook.Com. Retrieved on Jan 7, 2009
- ↑ MedicineNet > Definition of MCHC Last Editorial Review: 7/21/1999
- ↑ Rifkind, David; Cohen, Alan S. (2002). The Pediatric Abacus. Informa Healthcare. p. 54. ISBN 1-84214-147-3.