Iron Deficiency Anemia: A Practical Guide to Workup and Treatment
Clinical Practice Update — Ferritin Thresholds, GI Investigation, Oral vs IV Iron, Alternate-Day Dosing, and Long-Term Monitoring
This is an original clinical education article informed by current guidelines and evidence. See References below for source documents.
- Clinical Focus
- Diagnosis of iron deficiency, ferritin interpretation in inflammation, GI investigation pathways by sex and age, oral iron dosing and tolerability, IV iron indications, and post-treatment surveillance
- Target Audience
- Internists, primary care physicians, gastroenterologists, haematologists, residents, nurse practitioners
- Setting
- Primary care, gastroenterology clinic, haematology clinic, hospital inpatient
- Source Evidence
- •BSG 2021 Guidelines for the Management of Iron Deficiency Anaemia in Adults (Gut, 2021)
- •AGA 2021 Clinical Practice Guideline on the Gastrointestinal Evaluation of Iron Deficiency Anemia (Gastroenterology, 2020)
- •Pasricha SR et al. — Iron Deficiency (Lancet Seminar, 2021)
- •NICE Referral Guidelines for Suspected Cancer [NG12] and NICE CKS: Anaemia — Iron Deficiency
Key Clinical Takeaways
- 1Ferritin <45 ng/mL (45 µg/L) is the recommended diagnostic threshold for iron deficiency in anaemic patients — it has 85% sensitivity and 92% specificity → Confirming the Diagnosis
- 2Ferritin is an acute-phase reactant — it can be falsely normal in inflammation, CKD, liver disease, and malignancy. Check CRP and transferrin saturation when the clinical picture does not match → Confirming the Diagnosis
- 3All men and postmenopausal women with new unexplained IDA need urgent bidirectional GI endoscopy — roughly one in three will have underlying GI pathology, including cancer → Who Needs GI Investigation?
- 4Screen all IDA patients for coeliac disease — it is found in 3–5% of cases → Who Needs GI Investigation?
- 5Start oral iron immediately — do not defer treatment while awaiting investigations (unless colonoscopy is imminent) → Choosing Treatment
- 6One tablet once daily is as effective as multiple daily doses and much better tolerated — alternate-day dosing improves absorption further and reduces side effects → Choosing Treatment
- 7Check Hb at 2–4 weeks: a rise of ≥10 g/L confirms response. Continue iron for 3 months after Hb normalises to replete stores → Monitoring
- 8Switch to IV iron when oral is contraindicated, not tolerated, ineffective, or when rapid correction is needed (e.g., preoperative, active IBD, heart failure) → IV Iron
- 9In heart failure with iron deficiency, use IV iron (not oral) — oral iron does not improve prognosis in HF → Special Populations
- 10After treatment, monitor FBC every 6 months initially to detect recurrence — recurrent IDA requires re-investigation → Monitoring
How Do You Confirm Iron Deficiency?
Serum ferritin is the single most useful test. The AGA recommends a threshold of <45 ng/mL for diagnosing iron deficiency in anaemic patients (85% sensitivity, 92% specificity). The BSG notes that ferritin <15 µg/L is virtually diagnostic (specificity 99%), while levels of 15–45 µg/L are in a grey zone where clinical context matters. Because ferritin is an acute-phase reactant, it can be misleadingly normal in the presence of inflammation, liver disease, or malignancy.
Perform iron studies (ferritin, serum iron, TIBC, transferrin saturation) to confirm iron deficiency before initiating investigation. Use a ferritin threshold of <45 ng/mL (<45 µg/L) for diagnosis. When ferritin is equivocal (15–45), transferrin saturation <20% supports the diagnosis.
Strong RecModerate EvidenceBSG 2021AGA 2021Check CRP or ESR alongside ferritin. Elevated inflammatory markers suggest the ferritin may be falsely reassuring. In patients with chronic inflammation (IBD, CKD, rheumatological disease), consider iron deficiency likely if ferritin <100 µg/L.
Strong RecModerate EvidenceBSG 2021Consider a therapeutic trial of oral iron when iron studies are equivocal. An Hb rise of ≥10 g/L within 2 weeks of starting oral iron is highly suggestive of absolute iron deficiency.
Moderate RecModerate EvidenceBSG 2021Who Needs GI Investigation and What Should You Order?
Approximately one third of men and postmenopausal women with IDA will have an underlying GI pathology, most commonly in the upper or lower GI tract. Between 1% and 10% will have dual pathology. The investigation strategy depends on the patient’s sex, age, and menopausal status.
Investigation Strategy by Patient Group: A Decision Guide
| Patient Group | Baseline Workup | Endoscopy | If Endoscopy Negative | Practical Tips |
|---|---|---|---|---|
| Men and postmenopausal women | Coeliac serology, urinalysis, H. pylori testing | Urgent bidirectional: gastroscopy + colonoscopy (or CT colonography if colonoscopy unsuitable) | If IDA persists or recurs: capsule endoscopy of small bowel, renal tract imaging | Complete both upper and lower GI even if pathology found on one — dual pathology occurs in up to 10% |
| Premenopausal women | Coeliac serology, menstrual history, dietary assessment | Not routinely needed if menstrual/dietary cause identified. Investigate if: age >50, GI symptoms, family history of GI cancer, no response to iron | If IDA unresponsive to iron: refer for GI investigation | Menstrual loss is the most common cause, but do not assume — coeliac disease still found in 3–5% |
| Patients with IBD, CKD, or HF | Iron studies with ferritin <100 threshold for iron deficiency; CRP to assess inflammation | New IDA in these patients still warrants urgent GI investigation to exclude additional pathology | Manage iron deficiency with IV iron (oral iron often ineffective or poorly tolerated in IBD/HF/CKD) | In HF, IV iron improves symptoms even without anaemia (ferritin <100 or 100–299 with TSAT <20%) |
How Should You Treat Iron Deficiency Anemia?
Oral iron remains first-line for most patients. The key update from recent evidence is that once-daily or alternate-day dosing is as effective as the traditional two-to-three-times-daily regimen, with substantially better tolerability and possibly better fractional absorption (due to reduced hepcidin-mediated absorption block).
Start oral iron as one tablet daily of ferrous sulfate (65 mg elemental iron), ferrous fumarate (65 mg), or ferrous gluconate (35 mg). Do not defer treatment while awaiting investigation results, unless colonoscopy is imminent (iron can stain the bowel and impair views).
Strong RecModerate EvidenceBSG 2021If once-daily oral iron is not tolerated (GI side effects affect up to 30–50% of patients), reduce to alternate-day dosing. Evidence suggests alternate-day dosing may improve fractional iron absorption by avoiding the hepcidin rebound that occurs with daily dosing, while reducing GI side effects.
Moderate RecModerate EvidenceBSG 2021Prescribe IV iron (ferric carboxymaltose or iron derisomaltose) when oral iron is contraindicated, not tolerated, ineffective (no Hb response after 2–4 weeks), or when rapid correction is clinically urgent (e.g., preoperative, severe symptomatic anaemia, active IBD, heart failure, CKD on ESA). Ferric carboxymaltose and iron derisomaltose can replenish total body iron stores in 1–2 infusions.
Strong RecModerate EvidenceBSG 2021Clinical Decision Pathway
Evidence in Context
Where BSG and AGA Agree
Both recommend ferritin <45 as the diagnostic threshold, coeliac disease screening for all IDA patients, bidirectional endoscopy for men and postmenopausal women, H. pylori testing, starting oral iron promptly, and considering IV iron when oral fails. Both emphasise that faecal occult blood testing is not useful in the workup of IDA (it does not change management since endoscopy is indicated regardless).
Where They Differ
The AGA conditionally recommends against routine video capsule endoscopy in asymptomatic IDA with negative bidirectional endoscopy, reserving it for those with overt GI bleeding or persistent IDA. The BSG is more supportive of capsule endoscopy for recurrent or refractory IDA after negative bidirectional endoscopy. The BSG provides more detailed guidance on IV iron formulations and dosing, and specifically addresses IDA in HF, CKD, IBD, and post-bariatric surgery. The AGA explicitly recommends against routine use of hepcidin testing (insufficient evidence).
The Evidence for Alternate-Day Dosing
Iron absorption triggers a hepcidin surge that lasts approximately 24 hours, reducing absorption from subsequent doses taken the same day. Studies in iron-depleted women showed that alternate-day dosing of 60 mg elemental iron resulted in higher fractional absorption than daily dosing, with fewer GI side effects. While most of this evidence comes from non-anaemic iron-depleted populations, the BSG 2021 guideline incorporates this by recommending alternate-day dosing as a reasonable strategy for patients who do not tolerate daily iron.
References
- 1.Snook J, Bhala N, Beales ILP, et al. British Society of Gastroenterology guidelines for the management of iron deficiency anaemia in adults. Gut. 2021;70(11):2030–2051. doi:10.1136/gutjnl-2021-325210
- 2.Ko CW, Siddique SM, Patel A, et al. AGA Clinical Practice Guidelines on the Gastrointestinal Evaluation of Iron Deficiency Anemia. Gastroenterology. 2020;159(3):1085–1094. doi:10.1053/j.gastro.2020.06.046
- 3.Pasricha SR, Tye-Din J, Muckenthaler MU, Swinkels DW. Iron deficiency. Lancet. 2021;397(10270):233–248. doi:10.1016/S0140-6736(20)32594-0
- 4.Özdemir A, Arslanoğlu I, et al. Recommendations for diagnosis, treatment, and prevention of iron deficiency and iron deficiency anemia. Am J Hematol. 2024;99(8):1392–1412.
- 5.National Institute for Health and Care Excellence. Anaemia — iron deficiency. NICE Clinical Knowledge Summary. cks.nice.org.uk/topics/anaemia-iron-deficiency/
How to Read the Evidence Tags
Every recommendation carries two tags. These are Medaptly’s own simplified interpretations for educational clarity.
Recommendation Strength
| Tag | Meaning | In Practice |
|---|---|---|
| Strong Rec | Benefits clearly outweigh risks. | Standard practice. |
| Moderate Rec | Evidence favours benefit. | Most patients should receive this. |
| Conditional Rec | Right choice depends on individual. | Shared decision-making. |
| Against | Risks outweigh benefits. | Avoid. |
Evidence Quality
| Tag | Meaning | Confidence |
|---|---|---|
| High Evidence | Multiple RCTs or meta-analyses. | Very confident. |
| Moderate Evidence | Single RCT or large observational studies. | Reasonably confident. |
| Low Evidence | Expert consensus or small studies. | May change. |
These are Medaptly’s simplified interpretations. Consult original documents in References for full details.