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    MCH
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    MCH

    MCH — mean haemoglobin per red cell (27–31 pg): hypochromia, high values and laboratory artefacts.

    Mean corpuscular haemoglobin (MCH) is the average amount of haemoglobin in one red blood cell, expressed in picograms (pg, 10⁻¹² g). It shows how well the cells are "filled" with the oxygen-carrying protein. A low MCH (hypochromia) usually accompanies small red cells in iron deficiency and thalassaemia. A high MCH accompanies large red cells in vitamin B12 or folate deficiency.

    Complete blood countRed cell indicesHypochromia
    Adults27–31 pg
    CalculationHb (g/L) / RBC (×10¹²/L)
    Lowhypochromia
    Moves withMCV

    How MCH is obtained

    MCH is calculated, not measured directly: MCH (pg) = haemoglobin (g/L) / RBC (×10¹²/L). For example, a haemoglobin of 140 g/L and a red cell count of 4.8 ×10¹²/L give an MCH of about 29 pg. Because cell size and haemoglobin content are closely linked, MCH usually changes in the same direction as MCV. It carries limited additional information, but it is the basis of the traditional colour index (CI ≈ MCH / 33).

    MCH scale with hypochromic zone below 27 picograms, normal 27 to 31 and high above 31, with typical causes Mean corpuscular haemoglobin (pg per cell) Low (hypochromic) Normal High 27 pg31 pg • Iron deficiency• Thalassaemia trait• Anaemia of inflammation • Vitamin B12 / folate deficiency• Alcohol, liver disease• Artefact: lipaemia, cold agglutinins
    Figure 1. MCH follows red-cell size: small cells carry less haemoglobin, large cells carry more.

    Reference values

    A common adult reference range is 27–31 pg; some laboratories use up to 33 pg. Clinical Methods gives 29 ± 2 pg. Use your own laboratory's range.

    Low MCH

    Low MCH almost always accompanies low MCV. The most common causes are iron deficiency, thalassaemia trait and chronic inflammation. Ferritin, iron studies and, if needed, haemoglobin electrophoresis distinguish them. In iron deficiency, MCH may fall before haemoglobin does.

    High MCH

    High MCH is usually caused by macrocytosis: vitamin B12 or folate deficiency, alcohol, liver disease, hypothyroidism or medicines. A high MCH that does not fit the MCV may be an artefact: lipaemic (fatty) blood, very high white cell counts or cold agglutinins can falsely raise the measured haemoglobin or lower the red cell count.

    What to do

    An isolated, slightly abnormal MCH with normal haemoglobin, MCV and red cell count is rarely important. If MCH is abnormal together with anaemia or MCV changes, the doctor will look for the cause, usually starting with ferritin, vitamin B12 and folate.

    References

    1. Sarma PR. Red cell indices. In: Walker HK, Hall WD, Hurst JW, eds. Clinical Methods: The History, Physical, and Laboratory Examinations. 3rd ed. Boston: Butterworths; 1990. Chapter 152. ncbi.nlm.nih.gov/books/NBK260
    2. MedlinePlus. RBC indices. U.S. National Library of Medicine. medlineplus.gov/ency/article/003648.htm
    3. Camaschella C. Iron-deficiency anemia. N Engl J Med. 2015;372(19):1832–1843. doi:10.1056/NEJMra1401038

    This article is for general information and does not replace a consultation with a doctor. Laboratory results must be interpreted by a physician together with symptoms and other tests.

    Published on 11 February 2020