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Screening BODY HANDBOOK
Screening · §116
Ferritin and TSAT
Stubborn tiredness, hair in the drain, restless legs, brain fog you keep blaming on sleep: a lot of it is low iron. But ferritin, the test most doctors default to, misses it. Ferritin rises on its own whenever you're inflamed, overweight, drinking, or carrying a fatty liver, so it reads "normal" over an empty tank Dignass et al. 2018. Order a second number with it, transferrin saturation, and the pair tells you which of four things is true, one of which quietly decides how the next decade goes.
Screen · As-needed Evidence Moderate Chapter Screening

Ferritin is storage; TSAT is traffic. Ferritin normally tracks how much iron you have stashed, but inflammation makes the liver pump it out regardless, hiding an empty tank behind a normal reading. TSAT measures the share of your iron-carrying trucks that are loaded right now. Empty stores, TSAT drops; overflowing stores, it climbs. Two numbers pin down what one leaves ambiguous.

Read as a pair, they sort you into four. Both low: classic deficiency. Ferritin normal-or-high but TSAT low with inflammation around: the iron is there, locked inside cells where you can't use it. Both high, TSAT above 45%: possible iron overload, usually hereditary hemochromatosis 1. Or everything's fine.

The deficient group is bigger and quieter than people think. Roughly one in seven to one in ten premenopausal women is deficient by conservative cut-offs; endurance athletes run 20 to 35% 23. Heavy periods, a vegan diet, and frequent blood donation raise the odds too. Correcting a real deficiency lifts fatigue, exercise tolerance, and focus even when hemoglobin looks fine 4. For restless legs, iron comes before dopamine pills 5.

To treat, dose every other day. The first pill triggers hepcidin, which blocks absorption for a day or two, so a same-day dose mostly passes through. Take 65 mg of elemental iron on alternate days, empty stomach, with vitamin C; skip coffee, tea, dairy, and antacids within two hours. Recheck ferritin at three months 6.

The arc, if you were the deficient one. The first two weeks, nothing; the red cells haven't turned over. By four to six weeks the afternoon comes back and the flight of stairs stops counting. By three months ferritin is climbing and the shower drain clears. By six months, exercise improves on the same effort and the legs go quiet at night; the lift holds while you keep the iron up 7. If a routine TSAT caught overload early instead, the payoff is invisible: a few blood draws a year, and the cirrhosis and diabetes never arrive 8.

The fine print — when to skip it, and what people get wrong

"Low-normal ferritin is fine." Reference ranges often start at 12 to 15 ng/mL, where overt anemia becomes inevitable, not where symptoms start. The real threshold sits nearer 25 to 30 9. Tired with a ferritin of 22 and a "normal" flag: you are not fine. "High ferritin means overload, get phlebotomy." In the 200 to 800 range without a high TSAT, and with extra weight or daily wine in the picture, it's usually inflammation, not stored iron 10.

References
  1. 1Adams PC, Reboussin DM, Barton JC, et al. (2005). Hemochromatosis and Iron-Overload Screening in a Racially Diverse Population. New England Journal of Medicine. link
  2. 2Pasricha SR, Tye-Din J, Muckenthaler MU, Swinkels DW (2021). Iron deficiency. The Lancet. link
  3. 3Clénin G, Cordes M, Huber A, et al. (2015). Iron deficiency in sports — definition, influence on performance and therapy. Swiss Medical Weekly. link
  4. 4Pratt JJ, Khan KS (2016). Non-anaemic iron deficiency — a disease looking for recognition of diagnosis: a systematic review. European Journal of Haematology. link
  5. 5Allen RP, Picchietti DL, Auerbach M, et al. (2018). Evidence-based and consensus clinical practice guidelines for the iron treatment of restless legs syndrome/Willis-Ekbom disease in adults and children: an IRLSSG task force report. Sleep Medicine. link
  6. 6Stoffel NU, Cercamondi CI, Brittenham G, et al. (2017). Iron absorption from oral iron supplements given on consecutive versus alternate days and as single morning doses versus twice-daily split dosing in iron-depleted women: two open-label, randomised controlled trials. The Lancet Haematology. link
  7. 7Krayenbuehl PA, Battegay E, Breymann C, Furrer J, Schulthess G (2011). Intravenous iron for the treatment of fatigue in nonanemic, premenopausal women with low serum ferritin concentration. Blood. link
  8. 8Niederau C, Fischer R, Pürschel A, Stremmel W, Häussinger D, Strohmeyer G (1996). Long-term survival in patients with hereditary hemochromatosis. Gastroenterology. link
  9. 9Mei Z, Addo OY, Jefferds ME, et al. (2021). Physiologically based serum ferritin thresholds for iron deficiency in children and non-pregnant women: a US National Health and Nutrition Examination Surveys (NHANES) serial cross-sectional study. The Lancet Haematology. link
  10. 10Bacon BR, Adams PC, Kowdley KV, Powell LW, Tavill AS (2011). Diagnosis and management of hemochromatosis: 2011 practice guideline by the American Association for the Study of Liver Diseases. Hepatology. link
  11. 11Camaschella C (2015). Iron-Deficiency Anemia. New England Journal of Medicine. link
Related in the handbook (11)
Diagnosis
  • — A high ferritin with high saturation is the pattern that should trigger an HFE hemochromatosis check.
  • — Ferritin is exactly the number that exposes iron deficiency before anemia ever shows up.
  • — Restless legs is one condition where ferritin matters and the standard normal range misleads — aim for a higher target.
  • — Unexplained low ferritin in a menstruating woman often traces back to heavy periods — fibroids are a common, fixable cause worth ruling in.
Related
  • — If your ferritin is low for no clear reason, H. pylori belongs on the list of causes.
  • — Before trusting an A1c, it's worth knowing your iron status — deficiency distorts the result.
  • — The hidden tax of heavy periods is iron loss — check ferritin, not just a standard blood count.
  • — Ferritin is the poster child — a result inside 'normal' can still mean your iron is depleted.
  • — A fatty liver inflates ferritin, so a 'normal' result can hide empty iron stores — pair it with TSAT when MASLD is in the picture.
  • — Small cells with a wide spread point at iron deficiency — ferritin and TSAT are how you confirm it.
  • — Fatigue and brain fog can be thyroid or iron — if the thyroid is normal, iron is the next number to check.
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