You sleep eight hours and still wake up tired, and the stairs at work leave you more winded than they used to. Eventually you get a blood test. It comes back normal.
For many women, that’s where the trail goes cold. But a standard blood count is built to catch anemia, the late stage of running out of iron. It can miss the long stretch before that, when the body’s iron reserves are already close to empty and you can feel it.
Two different numbers
Most routine checkups include a complete blood count, which measures hemoglobin, the iron-containing protein in red blood cells that carries oxygen. When hemoglobin falls below the normal range, you have anemia.
Ferritin is something else. It’s a protein that stores iron, mostly in the liver, bone marrow and spleen, and the small amount circulating in the blood reflects how full those stores are. Your body draws down that reserve first, and it protects hemoglobin for as long as it can. Ferritin can drop for months, sometimes years, while hemoglobin holds steady.
Doctors call that in-between state iron deficiency without anemia. Ferritin isn’t part of a basic blood count, so nobody sees it unless someone orders it.
Why women run low
Iron leaves the body slowly, through shed skin and gut cells, except when there’s bleeding. For women, that usually means periods. Heavy menstrual bleeding is one of the most common reasons women of reproductive age run short, and many women don’t realize their periods count as heavy, because heavy is what they’ve always had.
Pregnancy is the other big drain. Official US intake recommendations reflect both: about 18 mg of iron a day for women aged 19 to 50, rising to 27 mg in pregnancy, against 8 mg for men and for women after menopause.
Diet matters too. Iron from meat, poultry and fish (called heme iron) is absorbed far more readily than the iron in beans, lentils, greens and fortified cereals. Vegetarians and vegans can absolutely get enough, but they’re generally advised to aim for nearly twice the standard amount to make up for the lower absorption. Frequent blood donors, endurance athletes and women with celiac disease or other gut conditions that interfere with absorption are also more likely to run low.
What it feels like
The symptoms are vague, which is part of the problem. Fatigue is the big one, along with shortness of breath on exertion, a racing heart, headaches and pale skin. The NHS lists less obvious signs as well: hair loss, a sore tongue, cracked corners of the mouth, brittle or spoon-shaped nails, restless legs at night, and pica, a craving to eat things that aren’t food. Chewing ice is a classic example.
None of these prove anything on their own. Tiredness has a hundred causes. But if several show up together, especially alongside heavy periods, it’s worth asking about iron specifically.
The cutoff that just moved
For years, many labs flagged ferritin as low only once it fell below about 15 ng/mL. Plenty of clinicians argued that was far too low, because people often have symptoms and depleted stores well above it.
In 2026 the American Society of Hematology published new diagnostic guidelines that raise the threshold. For most adults, including women who menstruate and women who are pregnant, the panel suggests treating ferritin at or below 30 ng/mL as iron deficiency. For women with heavy or irregular bleeding, symptoms, upcoming surgery or plans to get pregnant, it says a cutoff of up to 50 ng/mL may be reasonable.
A ferritin of 20 ng/mL might come back from the lab without a flag, and still count as iron deficiency under the new guidance.
A result in the high teens or low twenties may still be printed as within range on many lab reports, even though it now falls inside the deficiency zone. If you’ve been told your iron is “fine,” it’s worth asking what the actual ferritin number was.
Getting iron back in
If you’re deficient, food alone usually can’t refill stores quickly, and doctors typically recommend an iron supplement for a few months. The NHS says treatment commonly runs around six months, with repeat blood tests to check progress.
A few things make tablets work better:
- Take them with a source of vitamin C, such as orange juice, which helps absorption.
- Keep them away from tea, coffee, milk and calcium supplements by an hour or two, since these get in the way.
- Ask whether every-other-day dosing makes sense for you. Each dose triggers a rise in hepcidin, a hormone that blocks iron absorption for roughly a day, and small trials in iron-deficient women found more iron was absorbed overall when doses were spaced out.
Constipation, nausea, stomach pain and dark stools are common side effects. Taking iron with a little food can help, and alternate-day dosing seems easier on the stomach for some people. If tablets truly don’t work or can’t be tolerated, intravenous iron is an option your doctor can discuss.
Where the evidence is thinner
The new ferritin cutoffs rest mostly on low-certainty evidence, and the guideline itself says the thresholds are meant to inform judgment, not to trigger supplements automatically. Ferritin is also an imperfect gauge. It rises with inflammation, infection and liver disease, so it can look normal in someone who is actually low. In those cases doctors often add a second marker, transferrin saturation.
Extra iron also won’t boost energy in someone who isn’t deficient, and too much can build up in the body. That risk is higher in people with hereditary hemochromatosis, a fairly common genetic condition that causes iron overload, which is why doctors test before treating. Iron tablets are also a leading cause of poisoning in young children, so store them out of reach.
When to see a doctor
Persistent tiredness with heavy periods is reason enough to book an appointment and ask for ferritin alongside a blood count. Heavy bleeding itself deserves attention too, since it’s often treatable, and its pattern can change in perimenopause.
Iron deficiency in a woman who no longer has periods, or in anyone without an obvious cause, should be investigated, because slow bleeding in the stomach or bowel is a common culprit. Chest pain, fainting or severe breathlessness needs urgent care.
It’s easy to write off feeling depleted as the cost of a busy life, and sometimes that’s all it is. Sometimes, though, it’s a ferritin result nobody ordered, and that one can be fixed.
