Iron
What it measures, and what changes the number.
Serum iron measures the amount of iron circulating in the blood, most of it bound to the transport protein transferrin. It reflects iron in transit at that moment rather than the body's iron stores.
Because a single iron value varies a lot, it is usually ordered as part of an iron panel with ferritin, transferrin or TIBC, and transferrin saturation, which is calculated from iron and TIBC. It is also often read next to hemoglobin and other blood count results.
Serum iron follows a daily rhythm, tending to be higher in the morning, and it rises after iron rich meals, so many labs prefer a morning, fasting sample. Hemolysis can falsely raise the result. Labs may print it as Ferro, Hierro or IRON, TOTAL.
Often read alongside: Ferritin, Transferrin, TIBC, Transferrin saturation, Hemoglobin