Circulating iron — must be interpreted with ferritin, TIBC, and transferrin saturation, not in isolation.
Serum iron measures transferrin-bound iron in circulation. It fluctuates substantially through the day (peaks morning, lower evening) and with recent intake. Alone it is nearly useless — it must be interpreted with ferritin (storage iron) and TIBC/transferrin saturation (carrying capacity).
The useful picture is the full iron panel: ferritin, serum iron, TIBC, and transferrin saturation together.
Serum iron is influenced by: recent intake (rises after supplementation), time of day (higher AM), menstruation (drops women), GI losses, inflammation (drops during acute illness), and hemolysis (rises). Never interpret an isolated value.
Always order as a full iron panel. Fasting morning draw preferred for consistency. Retest 12 weeks after any supplementation change.
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Start tracking →Informational only — not medical advice. Reference ranges vary by lab and individual context. Work with a licensed provider to interpret your specific results.