Serum iron measures the amount of iron circulating in the blood bound to transferrin. A common reference range is about 60–170 μg/dL, though it varies by lab and by time of day.

By itself, serum iron is a noisy marker. It can shift with recent meals, inflammation, and daily variation, so it is rarely interpreted alone. Low values may occur with true iron deficiency, but also with inflammation or chronic disease. For healthy individuals, serum iron is best viewed as one piece of the iron picture, alongside ferritin, transferrin saturation, and total iron-binding capacity.