What is MCH?

MCH describes how much of the oxygen-carrying protein the bone marrow put into an average cell at the point that cell was built. A cell left short of haemoglobin carries less oxygen, whatever its size.

MCHC measures that same haemoglobin as a concentration, against the volume of the cell holding it, so MCH and MCHC differ by exactly one thing: cell size. MCV, the average size of a red cell, supplies it. Without it, MCH cannot say whether a cell holds little haemoglobin because it is small or because it was left sparsely filled at normal size.

Iron sets how much haemoglobin the marrow can pack into each new cell. MCH is an amount per cell rather than a density, so anything that makes cells larger raises it, and a shortage of vitamin B12 or folate does exactly that.

A red cell's haemoglobin is loaded as the cell is made, and nothing afterwards adds to it or takes it away. The average therefore trails the marrow by a full red cell lifespan, roughly 120 days. A year is longer than that lag, so each yearly reading describes cells built entirely since the last one. This is Do Health's monitoring schedule, not a general recommendation for everyone.