In an individual, levels fluctuate significantly due to diurnal variation and fasting status.

How quickly do ferritin levels change?

Parenteral iron

Intravenous infusion results in a rapid replenishment of iron stores with peak ferritin concentrations at 7–9 days after infusion. In our experience the haemoglobin should rise within 2–3 weeks in the majority of patients.

Can iron levels change day to day?

Iron levels change throughout the day. So it's best to do iron tests in the morning, when iron levels are highest.