MCH Calculator (Mean Corpuscular Haemoglobin)
MCH Calculator (Mean Corpuscular Haemoglobin)
Calculate mean corpuscular haemoglobin from haemoglobin and red cell count, and see why it usually tracks MCV rather than adding new information.
MCH
Haemoglobin per cellHaemoglobin 12.5 g/dL, red cell count 4.2 ×10¹²/L
Formula
- Hb
- haemoglobin concentration in g/dL
- RBC
- red cell count in ×10¹²/L
- × 10
- converts the Hb/RBC ratio into picograms per cell
- result
- pg — the average mass of haemoglobin carried by one red cell
Worked example
Haemoglobin 12.5 g/dL, red cell count 4.2 ×10¹²/L
12.5 ÷ 4.2 = 2.9762
2.9762 × 10 = 29.8 pg
MCH compared with MCV and MCHC
| Index | What it measures | Chief confounder |
|---|---|---|
| MCV | Mean cell volume | None — a direct volume measurement |
| MCH | Mean mass of haemoglobin per cell | None — an absolute mass, unaffected by dilution |
| MCHC | Mean haemoglobin concentration per cell | Plasma or sample dilution shifts the ratio without any change in cell haemoglobin |
Why MCH rarely changes the story MCV already told
Mean corpuscular haemoglobin is the average mass of haemoglobin carried by a single red cell, calculated from the same haemoglobin and red cell count that feed most other red cell indices. Because cell haemoglobin content rises and falls with cell volume in almost every anaemia, MCH tracks MCV closely — a microcytic cell is usually hypochromic, and a macrocytic cell usually carries more haemoglobin in absolute terms even though its concentration may be unremarkable. In routine practice this means MCH rarely adds information that MCV has not already given, and many clinicians read past it on the report.
Its real value shows up in the one situation where MCHC misleads: plasma dilution. MCHC divides haemoglobin by haematocrit, and haematocrit is sensitive to sample dilution from an intravenous line draw or to genuine haemodilution from fluid overload — the ratio moves even though nothing about the red cells has changed. MCH divides haemoglobin by red cell count instead, an absolute figure that dilution does not touch, so it stays a reliable measure of cell haemoglobin content when MCHC has been distorted. This is also why MCH is often preferred over MCHC when screening for thalassaemia trait: a low MCH below about 27 pg is a well-validated screening threshold, and it is not vulnerable to the sample-quality artefacts that can push a genuine thalassaemia trait sample’s MCHC in either direction.
Frequently asked questions
What is a normal MCH?
Roughly 27 to 33 pg in most adult reference ranges, though local laboratory ranges should be used. Below 27 pg is hypochromic; above 33 pg usually reflects macrocytosis rather than true hyperchromia.
Is MCH the same as MCHC?
No. MCH is the absolute mass of haemoglobin per cell in picograms; MCHC is the concentration of haemoglobin within the cell in g/dL. They are calculated from different denominators, which is why they can disagree.
Why is MCH preferred over MCHC for thalassaemia screening?
MCH is an absolute figure unaffected by plasma or sample dilution, while MCHC can be artificially raised or lowered by haemodilution, lipaemia or line-draw contamination. A low MCH is a more stable screening threshold.
Does MCH ever add information beyond MCV?
Rarely in isolation, since both usually move together. It is most useful as a cross-check when MCHC looks abnormal and you need to know whether the change is in the cell or in the sample.
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References
- Hoffbrand AV, Steensma DP. Hoffbrand’s Essential Haematology. 8th ed.
- International Council for Standardization in Haematology. Recommendations for red cell indices and reference intervals.