Iron deficiency anaemia in adults: confirming deficiency, finding the cause and replacing iron

Clinical scope and immediate priorities

Iron deficiency anaemia is common but should be treated as a diagnosis with a cause rather than merely a low haemoglobin that needs replacement. The immediate priorities are to confirm iron deficiency, assess symptom severity and haemodynamic stability, and identify gastrointestinal, menstrual, nutritional or malabsorptive causes that require separate investigation. Haematological abnormalities may represent primary disease, systemic illness, treatment toxicity or laboratory artefact. The urgency depends on symptoms, severity, trend and associated bleeding, thrombosis, infection or organ dysfunction. A blood count should be interpreted with the film, clinical context and relevant biochemical or coagulation studies rather than in isolation.

Recognition and differential diagnosis

Microcytosis and hypochromia support iron deficiency but may be absent early, while fatigue, exertional dyspnoea, palpitations, restless legs and pica can occur before severe anaemia. Blood loss is the dominant cause in many adults. Consider heavy menstrual bleeding, gastrointestinal malignancy or ulceration, inflammatory bowel disease, coeliac disease, pregnancy, bariatric surgery and restricted intake. Thalassaemia trait and anaemia of inflammation can mimic parts of the laboratory picture. The practical aim is to identify features that change urgency, distinguish common mimics and avoid anchoring on a single test result. Where the presentation is atypical, reassess the working diagnosis rather than forcing the findings to fit it.

Assessment and investigations

Ferritin is the most useful single marker of iron stores but rises with inflammation, liver disease and infection, so transferrin saturation and inflammatory markers can help when ferritin is equivocal. Review the blood film and reticulocyte response, and check renal function, B12/folate or haemolysis tests when the pattern is mixed. Investigation of the source should be age-, sex- and risk-appropriate, with gastrointestinal evaluation guided by national pathways and alarm features. Investigations should be sequenced so that urgent bedside information is obtained first, followed by tests that refine cause, severity or treatment choice. Trends, prior results and treatment effects often matter more than whether one value sits just inside or outside a reference range.

Initial and definitive management

Treat the cause and replenish iron. Oral iron is effective for many patients and lower-dose or alternate-day regimens can improve tolerance, while intravenous iron is appropriate when oral treatment is ineffective, poorly tolerated, absorption is impaired or rapid replacement is clinically important. Red-cell transfusion is reserved for selected patients with severe symptomatic anaemia or instability and does not replace the need to correct iron deficiency. Treatment should address reversible causes and immediate physiological risk while preserving options for definitive care. Medication selection requires attention to allergies, interactions, renal or hepatic function, pregnancy where relevant, and the possibility that a medicine suitable in one health system may not be first-line in another.

Escalation, complications and special situations

Urgent assessment is required for active bleeding, syncope, ischaemic symptoms, severe dyspnoea or haemodynamic compromise. Unexpected iron deficiency in an adult without an obvious benign explanation should trigger timely evaluation for occult gastrointestinal or gynaecological pathology. Failure to respond to adequate iron should prompt reassessment of adherence, ongoing loss, malabsorption and the original diagnosis. Escalate early when instability, organ dysfunction, rapidly progressive symptoms or a high-risk comorbidity is present. Frailty, pregnancy, immunosuppression, extremes of age and major renal or hepatic impairment can alter both presentation and treatment tolerance, so protocol-based care still requires individualisation.

International practice across English-speaking health systems

Across the United Kingdom, United States, Canada, Australia, New Zealand and Ireland, the core clinical principles are broadly similar, but drug licensing, formularies, emergency pathways, screening thresholds, referral criteria and professional scope can differ. Use the most recent national or regional guidance, local antimicrobial or medicines policy, and the relevant product information when an operational detail could change treatment. MDPDA therefore presents a common evidence-based framework and highlights areas that should be adapted locally rather than implying that one country’s pathway is universal.

Monitoring, follow-up and prevention

Follow-up should be purposeful rather than routine. Define what is being monitored, when it should be reassessed and what finding would change management. Review adherence and adverse effects, repeat objective measurements when they inform risk, and reconsider the diagnosis if the clinical course is inconsistent with expectations. Safety-netting should state which symptoms require urgent reassessment and which service should be contacted. For chronic disease, prevention, vaccination where relevant, smoking cessation, nutrition, physical activity and management of related cardiovascular or metabolic risk can be as important as disease-specific treatment. Recheck haemoglobin after treatment has had time to produce a marrow response and continue replacement long enough to replenish stores. A falling ferritin after apparently successful treatment suggests recurrent loss or inadequate maintenance and should not be managed indefinitely without revisiting the cause.

Common pitfalls and safety checks

Do not assume a low mean cell volume proves iron deficiency. Do not let iron replacement delay investigation of unexplained blood loss. Ferritin can appear normal or high in inflammatory states despite restricted iron availability. Transfusion may correct haemoglobin temporarily but does not replenish iron stores. A useful final check is to ask what dangerous alternative diagnosis could still explain the presentation, whether the patient has demonstrated an appropriate response to treatment, and whether the discharge or transfer plan is safe if symptoms recur.

Documentation, communication and shared decisions

Documentation should make the clinical reasoning visible. Record the key positive and negative findings, relevant risk stratification, important investigations, treatment rationale, discussions with the patient or family where appropriate, and the trigger for escalation or review. When care crosses settings, handover should identify unresolved diagnostic questions, medicines started or withheld, pending results and who is responsible for follow-up. Shared decisions are particularly important when more than one reasonable strategy exists or when treatment benefit must be balanced against bleeding, frailty, treatment burden or quality of life.

Implementation across care settings

Implementation across settings should preserve the trend in blood counts and coagulation results, not merely the latest value. Transfusion, anticoagulation and cytotoxic therapies create safety issues during handover, so document component requirements, antibody history, medicine indication and planned monitoring. Laboratory medicine, transfusion services and pharmacy are important clinical partners. When specialist testing is pending, provide clear thresholds for urgent reassessment rather than waiting passively for an outpatient result in a patient whose cytopenia, bleeding or thrombosis risk is changing.

Quality and patient-safety review

Before closing the episode of care, confirm that the working diagnosis remains consistent with the observed course, that high-risk alternatives have been considered, and that treatment has not introduced a new avoidable hazard. Review allergies, interactions, renal or hepatic constraints, pregnancy considerations where relevant, and the patient’s ability to follow the plan. The safest pathway is one in which the next clinician can understand what has been decided, what remains uncertain and which finding should trigger escalation.

Applying evidence to the individual patient

Guidelines provide a framework, but safe implementation depends on the patient’s baseline function, comorbidities, concurrent medicines, treatment goals and access to follow-up. Recommendations should be interpreted in light of absolute rather than relative benefit where possible, and clinicians should identify when the evidence base under-represents older people, pregnancy, severe kidney or liver impairment, multimorbidity or other groups. When two reasonable options exist, explain the trade-offs and document the reason for the selected approach. If local policy differs from an international recommendation, determine whether this reflects formulary, service configuration, licensing or genuinely different evidence. Reassessment is part of evidence-based care: a working diagnosis or treatment plan that no longer fits the clinical course should be revised rather than defended simply because it matched the initial pathway.