Condition Guide

Iron Deficiency Anaemia

Name: Iron Deficiency Anaemia: Causes & Blood Tests | HealthReview
Creator: Suman Konda
Published: 2026-07-05

Iron deficiency is the most common nutritional disorder in the world, affecting over 2 billion people. It causes fatigue, weakness and poor concentration. The key is finding WHY iron is low, not just replacing it.

Written by Suman Konda, PharmD, Clinical Pharmacist · Based on peer-reviewed sources · Editorial policy · Not medical advice

Last updated: 01 August 2026 · How we check our content

What is iron deficiency anaemia?

Iron deficiency anaemia (IDA) occurs when there is not enough iron in the body to produce adequate haemoglobin. Iron is essential for haemoglobin synthesis in red blood cells. Without it, red cells become small (microcytic) and pale (hypochromic) and carry less oxygen. IDA is the most common cause of anaemia worldwide and the most common nutritional deficiency. It develops in stages: first iron stores (ferritin) deplete, then transport iron (serum iron) falls, then finally haemoglobin falls and anaemia develops.

Iron deficiency blood test results

Test	Normal Range	Iron Deficiency Pattern
Haemoglobin (men)	13.5–17.5 g/dL	Low (anaemia)
Haemoglobin (women)	12.0–15.5 g/dL	Low (anaemia)
Ferritin	Men: 24–336 ng/mL; Women: 11–307 ng/mL	LOW (<30 ng/mL suggests deficiency)
Serum Iron	60–170 mcg/dL	Low
TIBC	250–370 mcg/dL	High (body makes more transferrin to scavenge iron)
Transferrin Saturation	20–50%	Low (<16% = iron deficiency)
MCV (mean cell volume)	80–100 fL	Low <80 fL (microcytic)

Causes of iron deficiency

Blood loss (most important cause)

Gastrointestinal bleeding is the most common cause in men and postmenopausal women: peptic ulcer, gastritis, colorectal cancer, colon polyps, inflammatory bowel disease, coeliac disease, hookworm. Heavy menstrual periods (menorrhagia) is the most common cause in premenopausal women. Regular blood donation, surgical blood loss and haematuria (blood in urine) are other sources.

Inadequate intake or absorption

Vegetarian/vegan diets (plant iron is less well absorbed than haem iron from meat), pregnancy and infancy (high demand), coeliac disease and Crohn's disease (malabsorption), gastric bypass surgery, long-term PPI use (reduces stomach acid needed for iron absorption).

Why is ferritin the first test to fall?

Ferritin is the iron storage protein. It is the body's iron reserve. When dietary iron or absorption is inadequate, the body first draws on these reserves. Ferritin falls BEFORE haemoglobin, serum iron, or MCV changes. This is why ferritin is the earliest and most sensitive marker of iron deficiency, detectable weeks to months before anaemia develops. A low ferritin even with normal haemoglobin still warrants investigation and treatment.

Treatment of iron deficiency

Treatment	When used	Notes
Oral iron (ferrous sulfate, ferrous gluconate)	Mild–moderate deficiency	Take on empty stomach if tolerated; vitamin C improves absorption; can cause GI side effects
IV iron infusion (ferric carboxymaltose, iron sucrose)	Severe deficiency, malabsorption, intolerance to oral	Single infusion replenishes stores rapidly
Dietary iron	Alongside supplements	Red meat, liver, dark leafy greens, lentils, fortified cereals

Crucially: always find and treat the CAUSE of iron deficiency. In men and postmenopausal women, unexplained IDA should prompt investigation for GI bleeding, a colonoscopy and upper GI endoscopy are usually arranged.

Questions to ask your doctor

Why am I iron deficient: is there a source of blood loss?
Do I need an endoscopy?
Should I take oral iron or IV iron?
How long before I feel better?
What foods will help my iron levels?

ICD-10-CM diagnosis codes

Iron deficiency is coded differently depending on whether anaemia has developed:

ICD-10-CM code	Description
D50.9	Iron deficiency anemia, unspecified
D50.0	Iron deficiency anemia secondary to chronic blood loss
D50.8	Other iron deficiency anemias
E61.1	Iron deficiency (without anemia)

Codes shown are from the current ICD-10-CM classification (FY2026) and are provided for general reference. Clinical coding is performed by trained coders using the full medical record.

References

The clinical information on this page is based on peer-reviewed sources indexed in PubMed, the biomedical literature database of the US National Library of Medicine.

Rusch JA, van der Westhuizen DJ, Gill RS, Louw VJ. Diagnosing iron deficiency: controversies and novel metrics. Best Pract Res Clin Anaesthesiol. 2023;37(4):451-467. doi:10.1016/j.bpa.2023.11.001 · PMID 39764832
Ford J. Red blood cell morphology. Int J Lab Hematol. 2013;35(3):351-7. doi:10.1111/ijlh.12082 · PMID 23480230
Iron Supplementation. In: StatPearls. Treasure Island (FL): StatPearls Publishing. NCBI Bookshelf NBK557376
Iron. In: StatPearls. Treasure Island (FL): StatPearls Publishing. NCBI Bookshelf NBK542171