You know the patient.
She’s tired — really tired. Not just “I stayed up too late scrolling” tired, but bone-deep fatigue. Maybe she’s struggling to keep up with work, skipping workouts she used to enjoy, or brushing off brain fog as stress. Her labs? “Normal.” Hemoglobin? Fine.
So we reassure, maybe suggest better sleep, maybe check a TSH and move on.
But here’s the uncomfortable truth: we might be missing one of the most common, most treatable conditions in medicine.
Iron deficiency.
Not anemia. Not yet, anyway. Just iron deficiency, and it matters more than we were trained to think.
Many of us were taught to think of iron deficiency as synonymous with anemia. No anemia? No problem.
That thinking is outdated.
Iron deficiency is a clinical syndrome that precedes anemia — sometimes by a long time. The body prioritizes hemoglobin production over everything else, so by the time anemia shows up, iron stores have already been depleted for a while.
And during that time? Patients feel it.
They may experience:
This isn’t subtle. This is quality-of-life altering.
And it’s incredibly common. Iron deficiency is the most common nutritional deficiency worldwide, and it disproportionately affects menstruating individuals and adolescents.
So if you’ve ever thought, “I have a lot of patients with these symptoms”… you’re probably right.
Let’s talk diagnostics, because this is where things often go sideways.
Iron panels can feel… messy. Serum iron, TIBC, transferrin saturation — it’s a lot. And to be honest, most of it isn’t that helpful in isolation.
If you remember one thing, make it this:
Ferritin is your best test.
Ferritin reflects iron stores. And while the “normal” range in your EMR might dip as low as 10–15 ng/mL, that doesn’t mean it’s clinically adequate.
Here’s a more practical framework:
In practice, many experts use <50 ng/mL as a threshold when patients have symptoms.
And yes — ferritin is an acute phase reactant. It can be falsely elevated in inflammation.
So in patients with chronic disease, consider:
Or, when in doubt: a therapeutic trial of iron can be diagnostic.
Some patients should immediately raise your suspicion.
Iron deficiency is especially common in:
And importantly: you don’t need anemia to justify testing.
If the story fits, check ferritin.
Diagnosing iron deficiency is just step one. The next question is: why?
In premenopausal patients, heavy menstrual bleeding is often the culprit. But don’t assume; that’s how we miss other causes.
Consider:
In men and postmenopausal patients, the threshold for GI workup should be lower, because the likelihood of pathology is higher.
Sometimes, “time” is part of the diagnostic process. Treat the suspected cause, replete iron, and reassess.
Once you’ve made the diagnosis, it’s time to treat.
Oral iron works. It’s cheap, accessible, and effective.
But let’s be honest, it’s also frustrating.
Patients struggle with:
Here’s a simplified approach:
One memorable takeaway from hematology: “Once a day, at dinner, with a meaty meal.” A bacon-wrapped iron pill is the way to go!
Simple enough to stick.
Expect:
If oral iron is the slow road, IV iron is the express lane.
And yet, many clinicians hesitate. That hesitation is understandable, but often outdated.
IV iron is:
The preferred formulation is low molecular weight iron dextran (INFeD). Give 1g in a single infusion — this is the fastest and cheapest method. INFeD is preferred over Injectafer (may cause hypophosphatemia) or Ferumoxytol (can cause artifacts on MRI). Following the infusion, you want to recheck a CBC and iron panel in about 6 weeks.
Consider IV iron for:
And the infamous “infusion reactions”?
With newer formulations, these reactions are not allergic. The “Fishbane reaction” (transient flushing, myalgias related to the complement pathway, not anaphylaxis) occurs in ~1% of patients, resolves quickly, and does not require epinephrine or antihistamines. Stop the infusion, wait 15 minutes, and restart at a slower rate. In fact, premedicating with antihistamines may make things worse, so do not premedicate despite what your EHR order sets may want you to believe!
Iron deficiency is easy to miss and easy to dismiss.
But when we catch it early, we can:
And maybe just as importantly, we validate our patients’ experiences.
That patient who felt brushed off?
Who was told everything was “normal”?
Sometimes, the most impactful thing we can say is:
“I think I know what’s going on — and we can treat it.”
If you’re walking into clinic and want a quick mental checklist, here it is:
Iron deficiency is bread-and-butter primary care, but it’s also one of those topics that’s easy to underestimate.
Once you start looking for it, you’ll find it. And when you treat it well, the impact can be profound.
And that’s the kind of medicine that keeps us coming back.
To hear more on this topic, subscribe and listen to our episode, "Don't Get Rusty: Iron Deficiency Diagnosis" on Primary Care Reviews and Perspectives podcast or listen on The Monthly Rounds on Spotify or Apple Podcasts.