What is Ferritin?

Ferritin holds iron in a safe form inside cells in the liver, spleen and bone marrow. The marrow draws on that store whenever it builds new red cells, and the store is what empties first when iron runs short, before the cells themselves are affected.

MCV gives the average size of a red cell and MCH the amount of haemoglobin inside it. Read alongside ferritin, the two say whether the marrow was working with enough iron to turn out cells of normal size, properly filled.

Iron taken in and absorbed from food builds the stores, while recent blood loss and periods of increased red cell production draw them down. Inflammation and infection work differently: they raise ferritin itself, independently of how much iron is actually there.

A short illness can lift ferritin within days, while the iron stores it otherwise reflects move over weeks to months as intake, loss and demand shift. A year between readings is long enough for the reserve itself to have changed, and long enough that a rise driven by one week's infection has passed rather than carrying into the next measurement. This is Do Health's monitoring schedule, not a general recommendation for everyone.