Iron studies —
beyond just
the haemoglobin.
A low haemoglobin can have many causes. Iron studies — ferritin, serum iron, TIBC, and transferrin saturation — tell your doctor precisely whether iron deficiency is the cause, and how depleted your stores actually are.
Dr. Sarah M. Chen, MD, FRCPC
Clinical Pathology, Hematology ·
The essentials — before you read the full guide below.
Ferritin = iron stores
Ferritin is a storage protein that reflects total body iron reserves. It's the most sensitive single test for iron deficiency — it falls before haemoglobin does.
Serum iron = iron in transit
Serum iron measures iron circulating in the blood right now, bound to transferrin. It fluctuates with meals and time of day — less reliable than ferritin alone.
TIBC = transfer capacity
Total iron-binding capacity measures how much iron transferrin could carry. In iron deficiency, TIBC rises (more empty carriers). In inflammation, TIBC falls.
Transferrin saturation
Calculated as (serum iron / TIBC) × 100. Below 16% confirms iron deficiency. Above 45–50% raises concern for iron overload (haemochromatosis).
Reference Ranges
What does your number
actually mean?
Use the interactive slider below, or read the range cards for a full clinical breakdown.
Iron Studies (Ferritin, Iron & TIBC) Reference Ranges
µg/L (Ferritin)Enter your result
Drag to see what your Iron Studies (Ferritin, Iron & TIBC) means
The Science
How iron deficiency develops in three stages
Iron deficiency doesn't happen suddenly — it progresses through three distinct stages over months to years. Understanding these stages explains why ferritin falls first, then serum iron, and only finally haemoglobin. By the time anaemia is visible on a CBC, iron stores have been empty for weeks.
Storage depletion — ferritin falls first
Iron stores drain from the bone marrow and liver. Ferritin falls below 30 µg/L. Haemoglobin and MCV are still normal. This stage is completely asymptomatic — only a ferritin test catches it.
Transport iron falls — TIBC rises
Serum iron drops, TIBC rises, and transferrin saturation falls below 16%. Red cell production becomes iron-limited. MCV may begin to fall. Fatigue may start but anaemia isn't yet present.
Anaemia appears — haemoglobin falls
Haemoglobin falls below reference range. RBCs become small (microcytic, low MCV) and pale (hypochromic, low MCH). Symptoms of anaemia are now present. This is the stage visible on CBC alone.
When to Test
Signs your doctor will
order this test
These are the most common reasons a Iron Studies (Ferritin, Iron & TIBC) test is requested — from symptoms to routine screening.
Persistent fatigue despite normal sleep
Iron deficiency impairs oxygen delivery and mitochondrial function — causing fatigue before anaemia develops. Many women dismiss this as normal.
Classic symptomPica — cravings for ice, dirt, or starch
Pica is a specific and often embarrassing symptom of iron deficiency. Craving ice (pagophagia) in particular is highly specific for iron deficiency.
Specific signBrittle nails or koilonychia (spoon nails)
Koilonychia — nails that curve upward — is a classic but less common sign of severe chronic iron deficiency. Brittle, ridged nails are more common.
Clinical signHeavy periods or pregnancy
Menstrual blood loss is the most common cause of iron deficiency in premenopausal women. Pregnancy markedly increases iron demand — screening at booking is standard.
Primary causeFollow-up after low haemoglobin
Iron studies are always the next step after discovering anaemia with low MCV on a CBC. They confirm iron deficiency and direct treatment.
Follow-up testCoeliac disease or IBD
Coeliac disease impairs iron absorption. Crohn's disease causes iron loss. Unexplained iron deficiency in a young adult warrants coeliac serology.
MalabsorptionTesting Schedule
How often should
you get tested?
Frequency depends on your current health status and your doctor's guidance.
Post-CBC follow-up
Iron studies are ordered as the next step after discovering anaemia with low MCV on a CBC.
During iron replacement
Ferritin is retested after 8–12 weeks of oral iron to confirm adequate response. Treatment typically continues until ferritin exceeds 50 µg/L.
Heavy menstrual blood loss
Women with heavy periods should have annual ferritin testing to catch depletion before anaemia develops.
Haemochromatosis
Ferritin and transferrin saturation are monitored every 3–6 months in hereditary haemochromatosis — venesection frequency is guided by ferritin level.
If Your Result Is Abnormal
Acting on iron study results
Treatment approach depends on the stage of deficiency and the underlying cause — not just the ferritin number.
Ferritin <30 → oral iron
Ferrous sulfate 200 mg (65 mg elemental iron) once daily on an empty stomach. Taken with vitamin C improves absorption. Expect haemoglobin to rise in 4–8 weeks; continue treatment 3 months after normalisation.
Ferrous sulfate + vitamin CIron deficiency + heavy bleeding → investigate source
In postmenopausal women and all men, unexplained iron deficiency requires GI investigation (endoscopy/colonoscopy) to exclude colorectal cancer or silent GI blood loss.
GI bleed screen in men/post-menopausalSevere deficiency or poor oral tolerance → IV iron
IV iron (ferric carboxymaltose or iron dextran) is used when oral iron fails, isn't tolerated, or when rapid repletion is needed (e.g. pre-op, IBD, CKD on EPO).
IV iron for malabsorption/intoleranceElevated ferritin + high transferrin sat → haemochromatosis
Ferritin above 300 (men) or 200 (women) with transferrin saturation above 45% warrants HFE gene testing for hereditary haemochromatosis. The HFE C282Y mutation accounts for >80% of cases.
HFE gene test