A ferritin of 22 ng/mL is technically "in range" at most US labs - and it will leave you exhausted, shedding hair, and unable to tolerate cardio. The reference range was built around "not anemic," not "functionally well." Here's the real ferritin target for women, why it gets missed, and how to fix it without bricking your gut.
Why "normal" ferritin isn't actually optimal
US lab reference ranges typically start ferritin at 10-15 ng/mL. That floor was set to avoid anemia, not to support energy, hair, training, or thyroid conversion. Functional medicine targets 70-100 ng/mL for active women; we use 50 as a hard floor.
Below ferritin 50 ng/mL: fatigue resistant to caffeine, restless legs at night, hair shedding 6-8 weeks after the deficiency starts, exercise tolerance drop, and impaired thyroid hormone conversion (T4 to T3 needs iron-dependent enzymes).
Hemoglobin can stay normal until ferritin drops below ~15-20 ng/mL. By then you've been symptomatic for months. Treating from hemoglobin alone is treating the late-stage signal, not the actual problem.
Who runs low
Menstruating women lose roughly 30-40 mg of iron per cycle; heavy cycles double that. Vegetarians and vegans rely on non-heme iron, which absorbs at 2-20% vs heme iron's 15-35%. Athletes lose iron through sweat and foot-strike hemolysis.
GLP-1 medications dampen appetite and often reduce red-meat intake unintentionally - we see ferritin slide in the first six months of GLP-1 use. Pregnancy and postpartum drop ferritin hard; recovery takes 12-24 months without supplementation.
Subclinical celiac, H. pylori, atrophic gastritis, and PPIs (omeprazole, pantoprazole) all impair iron absorption. "My iron is low and I can't figure out why" usually traces back here.
How to read the panel
Order ferritin with a CBC, transferrin saturation, and a CRP at the same draw. CRP matters because ferritin is an acute-phase reactant - inflammation falsely elevates it, masking deficiency. CRP under 1.0 mg/L means the ferritin number is reliable.
Transferrin saturation under 20% confirms iron-deficient erythropoiesis even if ferritin reads borderline. Pair it with MCV under 82 fL on the CBC and the picture is unambiguous.
If ferritin is high (over 200 ng/mL) without obvious cause, screen for hemochromatosis (HFE genetic test, transferrin saturation over 45%). High iron is its own problem.
Repletion that actually works
Oral iron: ferrous bisglycinate or ferrous sulfate, 18-65 mg elemental iron, every other day. Daily dosing raises hepcidin and tanks absorption - alternate-day dosing absorbs better with less GI upset. Take with vitamin C, away from coffee, tea, calcium, and thyroid medication by 2+ hours.
Recheck ferritin and CBC at 8-12 weeks. Most women see a 15-30 ng/mL ferritin rise per 8 weeks at therapeutic doses. If ferritin doesn't budge, the absorption pathway is the problem - investigate H. pylori, celiac, or switch to a different iron salt.
IV iron (ferric carboxymaltose, iron sucrose): reserved for severe deficiency, oral failure, malabsorption, heavy ongoing menstrual loss, or pre-surgical optimization. Faster repletion, requires provider review.
What to do now
If you're tired, shedding, or training and can't tolerate it - run the Advanced lab panel with ferritin, CBC, transferrin saturation, and CRP. Don't accept "your iron is fine" without seeing the ferritin number itself.
If you already know your ferritin is under 50, start oral iron at 18-65 mg every other day, retest in 8-12 weeks, and book the assessment if cycles are heavy or repletion stalls. A multivitamin with iron is rarely enough at the dose women need to climb out.