What ferritin actually is.

Ferritin is a protein that stores iron inside your cells. When the body has more iron than it currently needs, it tucks the surplus into ferritin, mostly in the liver, spleen and bone marrow. A blood ferritin test measures the small fraction that leaks into circulation, which closely tracks how much iron you have in storage overall.

"Ferritin is the savings account. Serum iron is the cash in your wallet. They tell different parts of the same story, and they don't always agree."

This is why ferritin is the most useful single iron test for women. Serum iron rises and falls with what you ate today. Ferritin reflects months of inflow and outflow — the slow story of whether your reserves are building or draining.

Why ferritin matters for women.

U.S. surveys find that low ferritin is several times more common in pre-menopausal women than in men of the same age. A meaningful share of women walk around with depleted iron stores while their hemoglobin still reads as normal — meaning a standard CBC won't catch the problem.

Years of low ferritin without overt anemia is the slow pattern most often missed at U.S. physicals. Women report fatigue, breathlessness on exertion, hair shedding, restless legs and brain fog. The lab paperwork comes back saying "normal." Often the marker that would have explained the picture — ferritin — was never ordered.

How to read the range.

Most U.S. labs report ferritin in nanograms per milliliter (ng/mL). The lab reference range for adult women typically runs from about 10 to 291. That range is statistical, not clinical — it includes the bottom 2.5% of asymptomatic women, many of whom feel exhausted.

The range most clinicians who specialise in women's health and fatigue work with is narrower. Many use 50 ng/mL as a working minimum for women with symptoms, with optimal often falling between 50 and 150 ng/mL. This is the gap a ferritin number lands in when the lab says "normal" but the woman holding the result says she's exhausted.

What may drive ferritin low.

  • Heavy or prolonged periods. The single most common driver in pre-menopausal women, and the most often unspoken.
  • Pregnancy and postpartum. Demand rises sharply during pregnancy; bleeding around birth adds to the cost.
  • Vegetarian or vegan eating without consistent attention to iron intake and absorption (vitamin C alongside meals, coffee/tea timing).
  • Endurance training combined with low iron intake. Foot-strike haemolysis and inflammation both contribute.
  • Frequent blood donation without sufficient recovery time between draws.
  • Gut conditions that reduce absorption: coeliac, inflammatory bowel disease, certain medications (PPIs, long-term).

What may drive it high: inflammation, infection, recent illness, alcohol use, fatty liver, hereditary haemochromatosis. Because ferritin rises with inflammation, a "normal" reading during illness can mask genuinely low stores. CRP alongside ferritin sorts the picture.

Worth asking your provider.

  • Could we run a full iron panel rather than ferritin alone? (Iron, TIBC, transferrin saturation, CBC.)
  • If my ferritin is below 50, is a 6–12 week trial of supplemental iron appropriate?
  • If periods are heavy or long, is that worth investigating alongside iron?
  • When should we re-test — six weeks, three months, longer?
  • Should we check CRP at the same time to rule out inflammation-masked low stores?
Educational only. Not medical advice. This guide is general health education and is not a substitute for personal medical advice, diagnosis or treatment. Always speak with a qualified healthcare provider about symptoms, blood results, supplement choices or treatment decisions, particularly if you are pregnant, breastfeeding, take medication, or have an existing medical condition.