Iron Deficiency: Why a Normal CBC Isn't Enough and What Your Ferritin Level Means
You're exhausted. Your hair is shedding. Your workouts feel harder than they should. Maybe you're cold all the time, getting headaches, feeling dizzy when you stand up, or suddenly wondering why chewing ice sounds like a legitimate hobby.
You get blood work done and hear:
“Your CBC is normal. You're not anemic.”
Great, except there's one problem.
You can be iron deficient without being anemic.
And this is one of the most common things I see women misunderstand about iron testing.
Iron deficiency and iron-deficiency anemia are related, but they are not the same diagnosis. In fact, the American Society of Hematology (ASH) points out that iron deficiency without anemia is nearly twice as common as iron deficiency with anemia.
So let's make iron testing make sense.
First: What Does Iron Deficiency Feel Like?
Iron isn't just sitting around waiting to make hemoglobin.
Your body uses iron for oxygen transport, energy production, muscle function, neurological function and numerous iron-dependent enzymes. That's one reason symptoms can start before your hemoglobin officially drops into the anemia range.
Some of the symptoms I would ask you about include:
Fatigue or feeling unusually depleted
Reduced exercise tolerance
Shortness of breath, especially with exertion
Weakness
Headaches
Dizziness or lightheadedness
Feeling cold
Brain fog or difficulty concentrating
Hair shedding or hair loss
Brittle nails
Restless legs
Heart pounding or a faster heart rate
Pica, especially craving or chewing ice
None of these automatically means IRON DEFICIENCY! Perimenopause alone could walk into the room carrying half this list. Same for hypothyroidism! 😂
That's why we test.
The ASH includes fatigue, weakness, dizziness, difficulty concentrating, shortness of breath, rapid heartbeat, headache, cold intolerance, restless legs and hair loss among symptoms associated with iron deficiency/iron-deficiency anemia.
Why Are You Low in Iron in the First Place?
Finding low iron is only step one.
I want to know WHY.
Most causes fit into four big buckets.
1. You're losing it.
Heavy periods are a huge one in women, especially during perimenopause when bleeding can become heavier or more erratic. But blood loss can also come from the gastrointestinal tract, blood donation, surgery or other sources.
2. You're not absorbing it.
Think celiac disease, inflammatory bowel disease, bariatric surgery or other gastrointestinal conditions that interfere with absorption. I’ve even seen significant small intestinal bacterial overgrowth (SIBO) cause major absorption issues.
3. You're not getting enough.
Iron intake can simply be inadequate for someone's needs, particularly with vegan, vegetarian, or certain restrictive diets and with increased requirements such as pregnancy.
4. You have iron, but your body isn't making it available very well.
This is where inflammation and our friend hepcidin enter the chat.
Blood loss is the major cause of iron-deficiency anemia, and gastrointestinal blood loss should not simply be written off, particularly in men and non-menstruating women.
Your CBC Does NOT Tell Me Your Iron Stores
A CBC, or complete blood count, tells us important things about your blood cells.
When I'm thinking about iron, I'm especially looking at:
RBC: red blood cell count
Hemoglobin (Hgb): the oxygen-carrying protein inside your red cells
Hematocrit (Hct): roughly how much of your blood volume is made up of red blood cells
MCV: average size of your red blood cells
MCH/MCHC: how much hemoglobin is contained in those cells
RDW: how much variation there is in red-cell size
As iron deficiency progresses toward iron-deficiency anemia, hemoglobin and hematocrit can fall and the red blood cells often become smaller and paler, reflected by changes in MCV and related indices.
But here's the important part:
Your iron stores can be depleted BEFORE your CBC becomes abnormal.
Think of it like your checking account and savings account.
Your body wants to keep enough money in checking to pay the bills, meaning enough hemoglobin to make red blood cells and transport oxygen.
So it starts draining savings.
Ferritin can fall while hemoglobin remains normal.
Eventually, if the iron deficit continues, the body can't maintain hemoglobin either.
That's when iron deficiency has progressed to iron-deficiency anemia.
This is why “your CBC is normal” does not automatically mean “your iron is fine.”
Ferritin: Your Iron Storage Marker
Ferritin is an iron-storage protein and serum ferritin is generally our most useful first marker of iron stores.
And we just got an important update here.
In September 2026, the American Society of Hematology released new guidelines recommending a ferritin threshold of ≤30 ng/mL for diagnosing iron deficiency in adults and menstruating or pregnant women, rather than relying on the older ≤15 ng/mL threshold.
Thank gawd!! I’ve long said the ferritin range is way too low as I’ve noticed tend to feel much better with a ferritin above 30 ng/mL and in many cases between 50-70 ng/mL.
The ASH also recommends different thresholds in certain higher-risk situations:
≤30 ng/mL: adults and menstruating/pregnant women shouldn’t be below this
≤50 ng/mL: certain high-risk groups, including people with heavy menstrual bleeding and pregnant women who are anemic shouldn’t be below this
With inflammation: ferritin <100 ng/mL OR transferrin saturation <20% may indicate iron deficiency.
That last one is REALLY important because ferritin has an annoying second job.
Ferritin is also an acute-phase reactant.
Inflammation can raise ferritin.
So someone can have iron that isn't adequately available to tissues while ferritin looks deceptively “fine” or even high.
Which brings us to...
Meet Hepcidin: The Iron Bouncer
If you've followed me for a while, you know I love a good biochemical bouncer. 😂
Hepcidin is the major hormone regulating systemic iron availability.
It's produced primarily by the liver and controls a protein called ferroportin, which is essentially the doorway that allows iron to leave intestinal cells and enter circulation and also allows stored/recycled iron to leave macrophages.
When hepcidin goes UP, ferroportin gets pulled down. Think of ferroportin like a port opening and closing based on hepcidin.
If your port or iron door closes less dietary iron gets into circulation + more iron gets trapped in storage cells.
Now your iron levels appear ‘low’ but really they are stuck inside the cell.
Inflammation, particularly signaling involving the inflammatory cytokine called IL-6, can increase hepcidin. That's part of the biology behind functional iron deficiency and anemia of inflammation/chronic disease.
If you have a lot of inflammation then you may have:
Ferritin: normal or high
Serum iron: low
Transferrin saturation: low
The iron may exist.
It just isn't getting where it's needed. It’s stuck inside.
And that's very different from someone who has simply depleted their iron stores through years of heavy menstrual bleeding.
Here's Another Cool Hepcidin Fact: More Iron Isn't Always More Absorption
Taking oral iron itself temporarily increases hepcidin, so this bouncer closes the port (ferroportin) and iron stays in the cell.
In a controlled study of iron-depleted young women, oral doses of ≥60 mg elemental iron increased hepcidin for about 24 hours and reduced fractional absorption of the subsequent dose by roughly 35–45%.
Which is one reason I’ve been moving away from the old-school mentality of:
IRON! THREE TIMES A DAY! GO!
For many people, lower-dose or alternate-day iron may improve fractional absorption and often improves tolerability as well. More isn't automatically better.
And no, this doesn't mean everyone should immediately switch their iron schedule. The dose and schedule depend on how deficient you are, why you're deficient, whether you're absorbing it and whether you're tolerating oral iron.
What Is Transferrin Saturation?
Now we're looking at the transport system.
Transferrin is the main protein carrying iron around in your blood.
Think of transferrin like the delivery trucks.
Transferrin saturation, or TSAT, tells us approximately what percentage of those trucks are actually carrying iron.
It's calculated from serum iron and total iron-binding capacity:
TSAT = serum iron ÷ TIBC × 100
A TSAT below about 20% means pretty empty trucks. This can indicate inadequate circulating iron availability, and it becomes especially useful when inflammation makes ferritin difficult to interpret.
So What Do I Actually Want Tested?
If I'm really evaluating iron status, I don't want only a CBC.
I generally want to see:
CBC
RBC
Hemoglobin
Hematocrit
MCV
MCH/MCHC
RDW
Iron studies
Ferritin
Serum iron
TIBC
Transferrin
Transferrin saturation (TSAT)
And depending on the situation, I may also care about:
Reticulocytes or reticulocyte hemoglobin to see what's happening with newly produced red cells.
hsCRP because inflammation changes how I interpret ferritin.
In more complicated cases, markers such as soluble transferrin receptor (sTfR) can sometimes help distinguish absolute iron deficiency from inflammatory iron restriction. Hepcidin itself is fascinating physiologically but isn't generally a routine clinical test.
This is why I don't love interpreting one iron marker in isolation.
I want the pattern and I want more than a CBC.
What About The Supplememt, Lactoferrin?
Lactoferrin is an iron-binding glycoprotein naturally found in secretions including breast milk and mucosal tissues. It's part of our innate immune system and has effects involving iron handling, inflammation and antimicrobial defense.
Supplemental bovine lactoferrin has been studied as an alternative or adjunct to conventional oral iron, particularly in people who don't tolerate standard iron very well.
A systematic review/meta-analysis of randomized trials found improvements in hemoglobin with oral bovine lactoferrin compared with ferrous sulfate in several studied populations, with generally good tolerability. But the studies were quite heterogeneous, and I would not interpret this as “lactoferrin is better than iron for everyone.”
The proposed benefit is interesting because lactoferrin may do more than simply deliver iron. Its effects on inflammatory signaling and iron regulation, potentially including the hepcidin-ferroportin system, may help improve iron availability in certain settings.
This is one I consider particularly interesting when someone says, “I don’t tolerate conventional oral iron well. I get GI issues” or “I have an inflammatory component to their iron picture.”
But again:
Figure out why the iron is low first.
You don't want to beautifully supplement someone's ferritin while ignoring the fact that they're bleeding every month, have undiagnosed celiac disease, or are losing blood somewhere in the GI tract.
The Big Takeaway
If you remember only three things, make them these:
Iron deficiency is NOT the same thing as anemia.
A normal CBC does NOT rule out iron deficiency.
And:
Don't just ask whether your iron is low. Ask WHY it's low.
Because replacing iron without understanding the reason it disappeared is like repeatedly filling a bathtub without wondering why the drain is open.
And now, thanks to the new 2026 American Society of Hematology guidelines, we have clearer diagnostic thresholds that should hopefully help catch iron deficiency before women spend years exhausted, shedding hair, struggling through workouts and being told everything looks “normal.”
Other citations:
Moretti D, Goede JS, Zeder C, et al. Oral iron supplements increase hepcidin and decrease iron absorption from daily or twice-daily doses in iron-depleted young women. Blood.2015;126(17):1981-1989. doi:10.1182/blood-2015-05-642223
Auerbach M, DeLoughery TG, Tirnauer JS. Iron deficiency in adults. JAMA.2025;333(20). doi:10.1001/jama.2025.0452