Low iron and heavy periods: the exhaustion that gets missed.
Heavy periods are the most common cause of low iron in Australian women of reproductive age. Blood loss each month empties your iron stores long before your haemoglobin falls, so you can feel wrung out while a standard blood count still reads as normal. Ferritin, the iron-store marker, is what shows it.
The result is a slow, grinding tiredness that gets put down to stress, work, or "hormones", when a simple blood test would have found it.
What counts as a heavy period?
Clinically, a heavy period (the medical term is heavy menstrual bleeding) is blood loss that interferes with your physical, social or emotional quality of life. It is defined by impact rather than by millilitres, because almost nobody measures their own blood loss. In practice, doctors ask about the practical signs.
- Soaking through a pad or tampon every one to two hours.
- Needing to double up on protection, or use a pad and a tampon together.
- Getting up overnight to change, or waking to leaks.
- Passing clots larger than a 50-cent coin.
- Bleeding for more than seven days.
- Planning your clothes or your weekend around your period.
Many women do not realise their periods are heavy, because they have never had anything else to compare them to. If two or three of those points describe you, your periods are likely heavy enough to be draining your iron, and ferritin is worth checking.
Why heavy periods drain iron
You lose iron in blood. Lose more each month than you absorb from food, and your stores slowly empty. The body protects the haemoglobin in your red cells for as long as it can, drawing on stored iron to keep making them. So you can be iron deficient for a long time before you become anaemic, and you will usually feel it well before a standard blood count picks it up.
That gap is where most women get missed. A full blood count comes back "normal", the conversation ends, and the tiredness carries on. Testing ferritin at the same time closes it.
What ferritin measures, and what iron studies add
Serum iron alone is a poor snapshot, because it swings with what you ate this morning. Ferritin is steadier. Its one weakness is that it rises with inflammation, so a normal ferritin during an infection can hide low stores. Our guide to ferritin and iron studies goes through each marker.
Ferritin ranges, and why "normal" can still be too low
Reference ranges for ferritin are wide and the lower end is debated. Below about 30 micrograms per litre is widely used in Australia to indicate low iron stores, and most large laboratories have moved to that lower limit, although some still report 15 or 20; the World Health Organization defines deficiency as under 15. That is why two women can be told opposite things about the same number.
| Ferritin (ug/L) | What it usually indicates | What a doctor does with it |
|---|---|---|
| Under 15 | Iron deficiency by almost any laboratory's definition | Confirms the cause of symptoms and looks for the source of loss |
| 15 to 30 | Low stores. Often reported as "normal" but frequently the explanation for symptoms | Reads it alongside your symptoms and your periods rather than in isolation |
| 30 to 100 | Generally adequate stores for a woman of reproductive age | Looks elsewhere if you are still exhausted, starting with thyroid |
| 100 to about 200 or 300 (the upper limit varies by laboratory) | Within range | Reads it with the rest of the iron studies and your symptoms |
| Above the laboratory's upper limit | Raised. Usually inflammation, and sometimes liver-related or metabolic causes | Repeats it when you are well. A result that stays high, particularly with a raised transferrin saturation, is checked further, including for the inherited iron-loading condition haemochromatosis |
Ranges vary by laboratory; your report shows the range your lab uses. Typical ranges on this page are drawn from Pathology Tests Explained (RCPA) and the sources listed below.
The symptoms women dismiss
- Exhaustion that sleep does not fix.
- Brain fog and poor concentration.
- Breathlessness on stairs, or a heart that races on mild effort.
- Hair shedding and brittle nails.
- Restless legs at night.
- Feeling cold when nobody else is.
- Low mood and a short fuse.
- Craving ice, or a strong urge to chew it.
Notice how much of that list overlaps with perimenopause and with an under-active thyroid. That overlap is why iron studies sit inside the perimenopause and menopause panel: heavy, erratic cycles in the transition years are a common route to low iron.
What else can be behind heavy periods
Low iron is the consequence. The bleeding itself deserves attention too, and a blood test helps sort out why it is happening. Fibroids, polyps and adenomyosis are structural causes a doctor investigates with an ultrasound rather than bloods. Other causes need blood tests of their own: an under-active thyroid shows on TSH, a bleeding disorder such as von Willebrand disease needs clotting studies rather than a hormone panel (particularly if periods have been heavy since your teens), and the cycles without ovulation that come with PCOS and with perimenopause show in the cycle hormones. Our guide to irregular periods covers that sorting process.
Testing tips
- Timing. Ferritin can be collected on any cycle day. No fasting is needed.
- Not while unwell. Ferritin rises with infection and inflammation, so leave it a couple of weeks after a bug.
- Mention iron supplements. They lift the reading, so tell your doctor what you take.
- Test the whole picture. Ferritin, iron studies and a full blood count together, plus TSH if fatigue is the main complaint.
What happens if your iron is low
Your KnowLuna doctor explains the result, what it means for your symptoms, and what the sensible next step is. Just as importantly, they look at the cause. If heavy periods are draining you, that is a conversation to have with your GP or a gynaecologist, and your KnowLuna report is written to be useful to them.
Common questions
What ferritin level is too low?
Below about 30 micrograms per litre is widely used in Australia to indicate low iron stores, and some laboratories still use 15, which is also the World Health Organization deficiency cut-off. Below that, the body has little iron in reserve even if haemoglobin is still normal. Your doctor reads the number alongside your symptoms, your periods and your full blood count.
Can you have low iron with normal haemoglobin?
Yes, and it is the most commonly missed pattern in women. Your body draws on stored iron to keep making red cells, so ferritin falls first and haemoglobin holds steady until the stores are nearly gone. This stage is called iron deficiency without anaemia, and it can cause fatigue, brain fog and hair shedding on its own.
What blood tests check for heavy period causes?
A useful set includes iron studies with ferritin, a full blood count, thyroid function and the cycle hormones, plus clotting studies where bleeding has been heavy since your teens. Blood tests cannot see fibroids or polyps, so a doctor may also arrange a pelvic ultrasound. The results narrow the list rather than settling it.
Is it worse to have low iron or low ferritin?
They are two views of the same problem. Ferritin reflects what you hold in reserve, while serum iron reflects what is circulating now and swings with your last meal. Low ferritin is the earlier and more reliable warning, which is why it is the marker doctors ask for when tiredness is the complaint.
How long does it take to feel better once low iron is found?
That depends on how low your stores are and what your doctor recommends, so it is a conversation to have with them. Rebuilding stores is usually measured in months rather than days, and a repeat ferritin some weeks later is how progress is checked. Addressing the blood loss matters as much as replacing the iron.
Sources and further reading
- Pathology Tests Explained (RCPA): ferritin
- Australian Commission on Safety and Quality in Health Care: Heavy Menstrual Bleeding Clinical Care Standard
- Jean Hailes for Women's Health: heavy periods
- Healthdirect: heavy periods
- Healthdirect: iron deficiency
- Better Health Channel: iron deficiency in adults
General information only, not medical advice. If your symptoms are severe or sudden, see a doctor promptly. This page does not replace a consultation with a doctor who knows your history; read our medical disclaimer.