A Low Ferritin with Heavy Periods
This is the largest single cause of iron deficiency in the world, and it is routinely treated as normal. Replacing the iron without addressing the loss guarantees the same result next year, so the page has two halves: getting your stores back, and deciding whether the bleeding itself is worth treating.
The pattern on your report
- Ferritin Low · marked Key
- Hemoglobin Low-normal Key
- MCV Low-normal Key
- Platelets High-normal Supporting
Printed as: Ferritin in ug/Lor ng/mL— The same figure under two names, and its printed lower limit sits below the level at which symptoms commonly appear.Hemoglobin in g/Lor g/dLMCV in fLPlatelets in x10^9/Lor x10^3/uL— Often drifts up in iron deficiency, and a raised value alongside a low ferritin is a useful hint that loss is ongoing.
Why the numbers look like this
Iron leaves the body almost exclusively in blood. Absorption from the gut is capped at a modest amount per day even when stores are empty, so the arithmetic is simple: if monthly losses exceed what the intestine can take up over the same period, stores fall regardless of diet.
Heavy menstrual bleeding pushes losses past that ceiling, and it does so month after month, so the deficit accumulates over years. That is why ferritin can be very low while hemoglobin still reads normal: the body has been drawing down reserves for a long time to protect the red cell count.
It also explains why dietary advice alone rarely fixes it. There is no diet that outpaces a loss the gut cannot match.
Not being flagged is not the same as normal
There is no laboratory definition of a heavy period, which is part of why it goes unaddressed. The practical definition is functional: bleeding that interferes with your life, or that soaks through protection every hour or two, passes clots larger than a coin, lasts more than seven or eight days, or requires doubling up on protection. Ferritin thresholds are also lower than symptoms warrant, so a value above the printed flag can still be causing fatigue.
What else on the report can hide this
The full blood count says how far this has gone. Ferritin low with a normal hemoglobin is iron deficiency without anemia, and it is genuinely symptomatic in many people. A falling hemoglobin with small cells means it has progressed.
Celiac serology is worth doing once even when the bleeding is obvious, because two causes can coexist and heavy periods are common enough to be a coincidence.
Thyroid function and a clotting assessment belong in the picture too. An underactive thyroid causes heavy bleeding, and an inherited bleeding disorder, most commonly von Willebrand disease, is present in a meaningful minority of women with heavy periods since adolescence. Both are missed for years because the bleeding gets attributed to gynecology alone.
The loss itself also has treatments that are not iron: tranexamic acid taken during the period, hormonal options including the intrauterine system, and investigation for fibroids. Those change the underlying arithmetic in a way supplements cannot.
What usually causes it
Listed from most to least common — not from most to least serious.
- Very common
Heavy menstrual bleeding with no structural cause
The commonest picture. Examination and imaging are normal, and the bleeding is still heavy enough to outpace absorption. It is treatable in its own right.
- Very common
Fibroids
Common, and more so with age and in women of African ancestry. Ultrasound identifies them, and treatment options range from medical to surgical.
- Common
Adenomyosis
Heavy bleeding with painful periods and a bulky uterus. Frequently diagnosed late, and imaging is what finds it.
- Common
An intrauterine copper device
Increases menstrual loss substantially. The hormonal system does the opposite and is often the treatment.
- Common
An inherited bleeding disorder
Von Willebrand disease most often. Suspected with heavy periods since the first one, easy bruising, nosebleeds, or heavy bleeding after dental work. Under-diagnosed for decades.
- Common
Hypothyroidism
Causes heavy bleeding and fatigue at once, so it can look like the consequence of the iron deficiency it is actually helping to cause. A TSH settles it.
- Uncommon
Polyps or endometrial hyperplasia
Irregular or intermenstrual bleeding alongside. More concerning after the menopause, where any bleeding needs assessment.
- Uncommon
Anticoagulants
Increase menstrual loss. Worth reviewing rather than accepting, since alternatives and adjuncts exist.
- Rare
Endometrial cancer
Suspected with bleeding between periods, after sex, or any bleeding after the menopause. The reason a changed pattern is assessed rather than attributed to normal variation.
What is usually checked next
- A specific bleeding history How often protection is changed, clot size, duration, and whether it has always been this way. More informative than any test and rarely asked in detail.
- TSH and celiac serology Both cause or compound this, and both are treatable. Worth doing even when the bleeding is an obvious explanation.
- Clotting screen and von Willebrand testing Indicated when periods have been heavy since adolescence or there is other bleeding, and it changes management of surgery and childbirth as well.
- Pelvic ultrasound Finds fibroids, adenomyosis and polyps, which have treatments that address the loss itself.
- Repeat ferritin three months after treatment starts Stores refill slowly, and stopping when the hemoglobin looks fine leaves the deficit in place for next year.
When to seek care sooner
- Emergency Bleeding heavy enough to soak through protection hourly, with dizziness or breathlessness
- Emergency Chest pain, breathlessness at rest, or fainting
- Soon Any vaginal bleeding after the menopause
- Soon Bleeding between periods or after sex
- Soon A sudden change in a pattern that had been stable for years
- Soon Heavy periods since the very first one, with easy bruising or nosebleeds
Questions worth bringing to your appointment
- Are my periods heavy by a clinical definition, or have I just got used to them?
- Should the bleeding itself be treated rather than only the iron?
- Have my thyroid and celiac status been checked?
- Given my periods have been like this since adolescence, should a bleeding disorder be excluded?
- How long should I stay on iron, and when should ferritin be rechecked?