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Section 2 of 6 · Open sections

Required section · Section 2 of 6

Iron supply, storage, and restriction

Transferrin carries iron in plasma, and marrow erythroid precursors incorporate available iron into heme. Ferritin reflects storage iron in uncomplicated deficiency. This physiology explains why depleted stores and impaired delivery can both produce iron-restricted erythropoiesis.

Ferritin is also an acute-phase reactant. Inflammation increases hepcidin and reduces iron export, leaving less iron available for erythropoiesis even when stored iron is present. A normal or increased ferritin therefore cannot by itself exclude iron deficiency during inflammation.

Transferrin saturation (TSAT) is serum iron ÷ total iron-binding capacity (TIBC) × 100. Serum iron has biologic variability and is not sufficient alone to classify iron status. Soluble transferrin receptor (sTfR) reflects erythroid iron demand and can support investigation of iron-restricted erythropoiesis when ferritin is confounded by inflammation; it is not interchangeable between assays and cannot establish iron deficiency alone.

Document whether TIBC is measured or calculated and apply the local formula, units, and rounding rule before releasing TSAT.

Illustrative drawing — this picture was drawn rather than captured.

Diagram showing transferrin carrying plasma iron to marrow for heme production and red-cell output, ferritin as storage, and inflammation reducing iron export through hepcidin.
Figure 1Iron availability connects transferrin transport, ferritin storage, marrow heme production, and hepcidin-mediated restriction.

Interpret an iron-restricted pattern as a structured comparison, not a single result.

  1. Verify context

    Review collection timing, transfusion, iron therapy, pregnancy, inflammation, renal disease, and local method fields.

  2. Compare the panel

    Read ferritin, iron, TIBC or transferrin, TSAT, CBC indices, and smear together.

  3. Choose a bounded action

    Release verified results and follow local policy for a comment, hemoglobin analysis, iron evaluation, or further investigation.

Knowledge checks

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Knowledge check 1

Serum iron is 5 micromol/L and TIBC is 76 micromol/L. What is the unrounded TSAT?

Choose one option.

Knowledge check 2

Which statements correctly describe ferritin in inflammation? Select all that apply.

Choose at least 2 options.

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