Mean corpuscular hemoglobin concentration: Difference between revisions
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{{Hatnote|Not to be confused with [[mean corpuscular hemoglobin]] per erythrocyte, although they are predictably correlated in healthy states.}} |
{{Hatnote|Not to be confused with [[mean corpuscular hemoglobin]] per erythrocyte, although they are predictably correlated in healthy states.}} |
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[[Image:1GZX Haemoglobin.png|thumb|[[hemoglobin]]]] |
[[Image:1GZX Haemoglobin.png|thumb|[[hemoglobin]]]] |
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The '''Mean corpuscular hemoglobin concentration''', a measure of the concentration of [[haemoglobin]] in a given volume of packed blood. |
The '''Mean corpuscular hemoglobin concentration''', a measure of the concentration of [[haemoglobin]] in a given volume of packed red blood cell. |
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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),<ref>{{MedlinePlusEncyclopedia|003648|RBC indices}}</ref> or between 4.81 and 5.58 mmol/L. It is thus a mass or molar concentration. |
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),<ref>{{MedlinePlusEncyclopedia|003648|RBC indices}}</ref> or between 4.81 and 5.58 mmol/L. It is thus a mass or molar concentration. |
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Revision as of 12:53, 14 January 2019
The Mean corpuscular hemoglobin concentration, a measure of the concentration of haemoglobin in a given volume of packed red blood cell.
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[2][3] 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 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:
- 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/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
- ^ MedlinePlus Encyclopedia: RBC indices
- ^ Blood Test Results - Normal Ranges Bloodbook.Com. Retrieved on Jan 7, 2009
- ^ MedicineNet > Definition of MCHC Last Editorial Review: 7/21/1999
- ^ 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.
- ^ Rifkind, David; Cohen, Alan S. (2002). The Pediatric Abacus. Informa Healthcare. p. 54. ISBN 1-84214-147-3.