Low Hemoglobin with Small Red Cells and a Low Ferritin
All three numbers pointing the same way is the classic picture of iron deficiency anemia, and by a wide margin the most common explanation for the combination. Of the anemias it is also the most fixable, which is the good news here. The iron itself is the easy part. The question that actually matters is where the iron went, because iron does not simply disappear.
The pattern on your report
- Hemoglobin Low · mild Key
- MCV Low · moderate Key
- Ferritin Low · marked Key
- RDW High Supporting
Printed as: Ferritin in ug/Lor ng/mL— The same figure under either name.Hemoglobin in g/Lor g/dL— A tenfold difference: 105 g/L is 10.5 g/dL.MCV in fLRDW in %— Reported as a percentage, sometimes labeled RDW-CV. A second form, RDW-SD, is reported in femtoliters and is a different number.
Why the numbers look like this
Hemoglobin is the cargo, iron is what the cargo is built from, and ferritin is the warehouse. When the warehouse empties, the marrow keeps building red cells but cannot fill them properly, so it makes them smaller and packs less hemoglobin into each one. Stores empty first, the hemoglobin falls next, and the cells only shrink once the shortage has been running long enough. Which is why a normal MCV early on does not rule iron deficiency out, and why all three numbers eventually line up.
So the panel is describing a process that has been running for months, not something that happened last week.
Not being flagged is not the same as normal
The hemoglobin threshold for anemia differs by sex and by guideline, commonly around 13 g/dL for men and 12 for women, with lower cut-offs in pregnancy. Ferritin thresholds vary more: WHO uses 15 ng/mL for depleted stores while UK gastroenterology guidance works nearer 30. A ferritin of 20 with a low hemoglobin and small cells is iron deficiency whatever line your laboratory drew.
What else on the report can hide this
The reticulocyte count says whether treatment is working before the hemoglobin does. It peaks around seven to ten days after starting iron, so that is when it is worth drawing; a flat count at that point means the iron is not being absorbed or not being taken. A CRP matters here for the opposite reason it usually does: inflammation lifts ferritin, so a low ferritin alongside a raised CRP means stores are emptier than the number says. In anyone whose red cells stay small after the iron is replaced, thalassemia trait may be sitting underneath the deficiency, which a hemoglobin electrophoresis settles once the iron is corrected.
What usually causes it
Listed from most to least common — not from most to least serious.
- Very common
Menstrual blood loss — in menstruating people
Heavy or prolonged periods, clots, or flooding through protection. The leading cause in this group by a wide margin, and it usually needs no search for another source.
- Very common
Not enough absorbable iron in the diet
Little or no red meat, or a vegetarian or vegan diet. Plant iron absorbs several times less efficiently, and tea or coffee with meals reduces it further.
- Common
Pregnancy and breastfeeding — in pregnancy and the year after
Demand climbs steeply from the second trimester. Expected, but it still needs treating rather than waiting out.
- Common
Bleeding in the gut
The cause that must be excluded in men and in women past the menopause, because there is no routine physiological source in either group. It is frequently silent, and normal-looking stool does not rule it out.
- Common
Poor absorption
Celiac disease, Helicobacter pylori, long-term acid-suppressing drugs, or previous stomach or bowel surgery. Suspect it when intake looks adequate and no bleeding is found.
- Common
Frequent blood donation
A whole-blood donation removes a substantial amount of iron, and hemoglobin can recover enough to pass donor screening while stores stay flat.
- Common
Hookworm or other intestinal parasites — in people living in or returning from endemic regions
A leading cause of iron deficiency in endemic regions, and easily missed where it is rare. Ask about residence and travel; stool testing settles it.
- Common
Endurance training load — in high-volume runners, cyclists and triathletes
Exercise raises hepcidin and blunts iron absorption for hours afterwards, with foot-strike hemolysis and sweat losses adding to it.
- Uncommon
Long-term aspirin or anti-inflammatory use
Causes slow gastric blood loss that produces no symptoms at all until the count falls.
- Uncommon
A tumor of the stomach or bowel
The reason unexplained iron deficiency in an older adult is investigated rather than simply treated. Weight loss or a change in bowel habit alongside makes it more pressing.
What is usually checked next
- Celiac serology with a total IgA Screens the commonest absorptive cause. The total IgA has to go with it, because IgA deficiency makes the celiac test read negative when it should not.
- Stool test for hidden blood, and endoscopy where indicated Looks for the source. Which of these is appropriate depends on your age, sex and symptoms, and that is the conversation to have.
- Reticulocyte count seven to ten days after starting iron Catches the response at its peak, weeks before the hemoglobin will show it. Drawn at two weeks it has often already fallen back.
- Repeat ferritin after three months of treatment Shows whether stores are refilling. Hemoglobin corrects long before ferritin does, so stopping when the hemoglobin normalizes leaves the stores still empty.
When to seek care sooner
- Emergency Vomiting blood, or stools that are black and tarry
- Emergency Chest pain, breathlessness at rest, or fainting
- Same day Visible blood in the stool
- Soon Unintentional weight loss, or a change in bowel habit lasting several weeks
- Soon Iron deficiency in a man or a woman past the menopause with no source identified
- Soon Difficulty swallowing
Questions worth bringing to your appointment
- Given my age and sex, do we need to look for a source of blood loss?
- Should I be screened for celiac disease?
- Which iron preparation, and should I take it daily or every other day?
- What ferritin are we aiming for, and how long should I stay on treatment after the hemoglobin recovers?
- If my periods are the cause, is that worth treating in its own right?