Iron reliably restores energy, exercise capacity, and oxygen-carrying only when a genuine shortage exists — most often in menstruating women, endurance athletes, blood donors, and those eating little meat. For people who already have enough, added iron brings only risk, since surplus builds up over a lifetime and has been tied to faster aging. Testing first is essential. (Full Review)
| Marker | Target | Why |
|---|---|---|
| Ferritin | ~50–150 ng/mL | Total iron stores; key decision variable |
| Transferrin saturation (TSAT) | 20–40% | Shows how much iron is available for use |
| Serum iron | Within reference, with TSAT | Circulating iron at the moment of draw |
| Total iron-binding capacity (TIBC) | Upper-normal in deficiency | Indirect measure of transferrin; rises when iron is low |
| Hemoglobin / CBC | Sex-specific normal | Detects anemia and tracks treatment response |
| Soluble transferrin receptor (sTfR) | Within assay reference | Distinguishes true iron deficiency from inflammation |
| C-reactive protein (CRP) | <1–3 mg/L | Flags inflammation that can distort ferritin |
Cadence: Recheck ferritin, transferrin saturation, and hemoglobin at 8–12 weeks, then every 3–6 months until stores are restored; annual check once stopped and stable