If you have ever been told your iron is fine while feeling tired, foggy and flat, this is the post for you.
There is a reasonable chance nobody measured the thing that would have explained it.
Haemoglobin and ferritin are different tests
A standard full blood count measures haemoglobin, which is the iron carrying protein in your red blood cells. It tells you whether you are anaemic.
Ferritin measures stored iron. It is a separate test, and it is not automatically included.
The distinction matters because your body protects haemoglobin. When iron runs low, stores are drawn down first, and haemoglobin is maintained for as long as possible. So stores can be substantially depleted while a full blood count still comes back normal.
That stage has a name, iron deficiency without anaemia, and it is where a lot of women sit. Tired, foggy, low on stamina, and told everything looks fine.
The two questions
First: was ferritin actually tested? If only a full blood count was done, stored iron was not measured at all.
Second: what was the number? Not whether it was in range, the actual figure.
Reference ranges for ferritin are wide, and the bottom of a laboratory range is a long way from comfortable. Where you sit within the range is the useful information, and a result at the very bottom can be reported as normal.
Neither of these is demanding anything. They are reasonable questions about your own results, and any good GP will answer them.
Write it down
Iron is far more useful as a trend of data over time, rather than as a snapshot.
Keep the number and the date somewhere you will find it. A single ferritin result tells you where you are. Two results a year apart tell you which direction you are going, which is a much more useful thing to know, particularly through the years when losses are heaviest.
A note on interpretation
Ferritin is also an inflammatory marker, which means it rises during infection, inflammation and some chronic conditions. So a result taken while you are unwell can look reassuring when it is not.
That is one of several reasons this is a conversation with your GP rather than something to interpret yourself off a printout. The purpose of asking is to be better informed in that conversation, not to replace it.
The takeaway: Haemoglobin and ferritin measure different things, and a normal full blood count does not mean your iron stores are adequate. Ask whether ferritin was tested and ask for the number rather than whether it was in range. Record it, because the trend matters more than any single result.
The science behind this post:
- World Health Organization (2020). WHO guideline on use of ferritin concentrations to assess iron status in individuals and populations. Ferritin is the recommended marker of iron stores, and concentrations rise in the presence of infection and inflammation.
- Royal College of Pathologists of Australasia. Iron studies: interpretation of ferritin, transferrin saturation and full blood count in the assessment of iron status. rcpa.edu.au
- National Health and Medical Research Council. Nutrient Reference Values for Australia and New Zealand: Iron. Requirements by sex and life stage. nrv.gov.au