Clinical Guides
Approach to Anaemia
A mechanism-led guide to stabilising, classifying and investigating anaemia across adults, pregnancy and childhood, with practical interpretation of red-cell indices, reticulocytes, iron, vitamin, haemolysis and marrow findings in India.
MedNext Academy | 13 min read
Approach to Anaemia
A mechanism-led guide to stabilising, classifying and investigating anaemia across adults, pregnancy and childhood, with practical interpretation of red-cell indices, reticulocytes, iron, vitamin, haemolysis and marrow findings in India.
Summary
Anaemia is a reduced haemoglobin concentration for the person's age, sex and physiological state; it is a finding, not a final diagnosis. Confirm an unexpected result, but do not delay resuscitation when bleeding, shock, myocardial ischaemia, severe hypoxaemia or rapid haemolysis is present. The immediate assessment asks two questions: is oxygen delivery failing now, and is blood being lost or destroyed rapidly? Symptoms, trajectory, comorbidity and haemodynamic state matter more than a single universal transfusion number.
Once stable, classify the mechanism rather than treating every low haemoglobin as iron deficiency. The complete blood count, mean corpuscular volume, red-cell distribution width, reticulocyte response and peripheral smear provide the first map. A low or inappropriately normal reticulocyte response suggests impaired production; an appropriate rise suggests blood loss, haemolysis or recovery. Microcytosis directs attention to iron deficiency, thalassaemia and inflammation; macrocytosis to vitamin B12 or folate deficiency, medicines, alcohol, liver or thyroid disease, reticulocytosis and marrow disorders. Normocytosis does not exclude iron deficiency or mixed disease.
Cause-finding and replacement proceed together when safe. Assess bleeding, nutrition, absorption, infection, inflammation, kidney disease, pregnancy, inherited red-cell disorders and marrow failure. Iron, vitamin B12, folate, erythropoiesis-stimulating treatment and transfusion have distinct indications and hazards. This educational guide supports structured reasoning but cannot select a transfusion threshold, iron formulation or paediatric or pregnancy regimen for an individual patient.
How Common Is It?
Anaemia is a major global and Indian health burden, concentrated in young children and women but clinically important in every age group. WHO's 2025 estimates track trends in women aged 15 to 49 through 2023 and warn that comparisons with older estimate rounds require care because methods and data inputs change. Prevalence estimates describe populations; they do not identify iron deficiency in an individual and cannot replace a clinical work-up.
Indian NFHS-5 data, reproduced in the Government of India's National Health Profile 2023, reported anaemia in 67.1% of children aged 6 to 59 months, 57.2% of non-pregnant women aged 15 to 49, 52.2% of pregnant women in that age range and 57.0% of all women aged 15 to 49. These survey indicators used specified haemoglobin thresholds and capillary sampling. They should not be mechanically compared with venous laboratory results, nor interpreted as the prevalence of iron deficiency. The figures demonstrate programme-scale need while preserving the distinction between anaemia and its many causes.
Hospital populations differ sharply from survey populations. Older adults may have chronic kidney disease, inflammation, gastrointestinal blood loss, cancer or clonal marrow disease; tertiary paediatric units see haemoglobinopathies and treatment-related anaemia; obstetric services see nutritional deficiency and acute haemorrhage. Local case mix and access to diagnostics influence what is detected. A high background prevalence raises the value of reliable screening and follow-up, but it must never normalise severe symptoms or justify empirical iron indefinitely without checking response and cause.
Risk Factors
Risk factors are best organised by reduced production, blood loss and increased destruction. Nutritional or absorptive risks include low iron or vitamin intake, food insecurity, restrictive diets, infancy, adolescence, pregnancy, repeated short inter-pregnancy intervals, coeliac disease, autoimmune gastritis, inflammatory bowel disease and gastrointestinal surgery. Acid suppression can contribute in selected patients. Iron requirement rises during growth and pregnancy; this increases susceptibility but does not make every anaemia nutritional.
Chronic or occult blood loss may arise from heavy menstrual bleeding, postpartum haemorrhage, gastrointestinal ulceration, malignancy, inflammatory bowel disease, parasites, urinary bleeding, repeated phlebotomy or blood donation. Aspirin, non-steroidal anti-inflammatory drugs, anticoagulants and antiplatelet medicines can expose or worsen bleeding. In men and postmenopausal women, unexplained iron deficiency warrants particular attention to gastrointestinal causes rather than repeated replacement alone.
Impaired production occurs with chronic kidney disease, inflammation, tuberculosis, HIV, malignancy, endocrine disease, marrow infiltration, aplasia, myelodysplasia and chemotherapy. Medicines may cause marrow suppression, haemolysis, macrocytosis or impaired vitamin metabolism. Haemolytic risk includes malaria, immune disease, incompatible transfusion, mechanical valves, burns, oxidant exposure in glucose-6-phosphate dehydrogenase deficiency, membrane disorders, sickle disorders and thalassaemia. Family origin and history guide haemoglobinopathy testing without stereotyping. Children with poor growth, recurrent infection or congenital anomalies and adults with pancytopenia, constitutional symptoms or splenomegaly require a broader marrow and systemic assessment. Mixed mechanisms are common, especially in pregnancy, chronic infection, kidney disease and cancer.
Diagnosis
History
Establish onset, trajectory and functional impact: fatigue, exertional dyspnoea, palpitation, dizziness, syncope, chest discomfort, reduced school or work performance and pica. Ask directly about haematemesis, melaena, rectal or urinary blood, epistaxis, bruising, heavy menstruation, pregnancy, postpartum loss, surgery, trauma, donation and parasites. Record diet, weight change, dysphagia, bowel symptoms, fever, night sweats, bone pain, jaundice, dark urine, medicines, alcohol, chronic disease, infection exposure and family history. Neuropathy, gait change or cognitive symptoms increase concern for vitamin B12 deficiency. In children, include feeding, growth, development and newborn or family history.
Examination
Assess airway, breathing, pulse, blood pressure, orthostatic tolerance, perfusion, mental state, oxygen saturation and evidence of active bleeding before detailed signs. Pallor is neither sensitive nor specific. Look for jaundice, petechiae, glossitis, angular cheilitis, koilonychia, oedema, lymphadenopathy, hepatosplenomegaly, abdominal mass, cardiac failure, infection and neurological impairment. In pregnancy assess gestation and obstetric danger signs; in children record growth and developmental context. Rectal, pelvic or other intimate examination requires a clinical indication, consent, privacy and an appropriate chaperone.
Investigations
Repeat the complete count when sampling error or dilution is plausible, then interpret haemoglobin with MCV, MCH, RDW, white cells and platelets. Review a peripheral smear and obtain a reticulocyte count, ideally an age- and anaemia-adjusted response. Iron studies should include ferritin; interpret it with inflammation and consider transferrin saturation or other available markers. Test vitamin B12 and folate when indicated. Suspected haemolysis prompts bilirubin fractions, lactate dehydrogenase, haptoglobin where available, urine findings and a direct antiglobulin test selected by phenotype. Kidney, liver and thyroid tests, CRP, infection studies, haemoglobin analysis, stool or endoscopic evaluation and marrow examination are targeted, not automatic panels. Preserve pre-transfusion samples where they may establish cause.
Differential Diagnosis
Microcytic anaemia includes iron deficiency, thalassaemia, inflammation with iron restriction, sideroblastic processes and lead toxicity. Ferritin that is unequivocally low supports iron deficiency, while a normal or raised value does not exclude it during inflammation, liver disease or recent iron therapy. A relatively high red-cell count with marked microcytosis can suggest thalassaemia trait, but indices are screening clues rather than a substitute for haemoglobin analysis and iron assessment. More than one disorder may coexist.
Normocytic anaemia includes acute blood loss, early iron deficiency, inflammation, chronic kidney disease, endocrine disease, haemolysis, marrow infiltration and mixed microcytic and macrocytic states. The reticulocyte response separates many production problems from loss or destruction, provided it is interpreted against the degree of anaemia. Haemolysis is supported by a coherent pattern of reticulocytosis, indirect hyperbilirubinaemia, raised lactate dehydrogenase, low haptoglobin and smear findings; none is perfectly specific. Fragmented cells with thrombocytopenia raise thrombotic microangiopathy or DIC and require urgent clinical correlation.
Macrocytosis may follow vitamin B12 or folate deficiency, alcohol, liver disease, hypothyroidism, medicines, reticulocytosis or myelodysplasia. Neurological B12 deficiency can occur without severe anaemia. Pancytopenia or additional cytopenias widen the differential to aplasia, leukaemia, megaloblastic change, hypersplenism, infection, autoimmune disease and infiltrative marrow disorders. Spurious results include cold agglutinins, lipaemia and sampling dilution. Anaemia of pregnancy must be distinguished from expected plasma-volume expansion, and paediatric results must use age-appropriate reference ranges. The final assessment should state severity, tempo, morphology, reticulocyte response, leading mechanism, evidence for cause and unresolved alternatives.
Management
Treat physiological compromise and the source simultaneously. Active major haemorrhage requires an emergency bleeding pathway, vascular access, blood-bank notification, source control, warming, calcium and coagulation assessment according to local massive-haemorrhage protocol. Red-cell transfusion is based on haemodynamics, ongoing loss, symptoms, cardiac or respiratory comorbidity and expected trajectory, not haemoglobin alone. Restrictive strategies suit many stable patients, but trial thresholds do not override shock, acute coronary ischaemia or individual physiology. Transfusion temporarily improves oxygen carriage; it does not replace iron or identify the cause.
For stable iron deficiency, begin appropriate oral iron while investigating the source unless urgent diagnostics require a different sequence. Check adherence, formulation, timing, ongoing loss, inflammation and malabsorption when response is inadequate. Intravenous iron is considered when oral treatment is not tolerated or absorbed, ongoing needs exceed replacement, or rapid repletion is clinically important; product reactions and calculation errors require monitored administration. Replace vitamin B12 promptly when deficiency is likely, especially with neurological findings, and do not use folate alone until clinically important B12 deficiency has been addressed.
Treat the mechanism: control menstrual or gastrointestinal loss, manage parasites or infection where established, address inflammatory disease, optimise chronic kidney disease care, stop a causal medicine only with a safe alternative, and refer haemoglobinopathy or marrow disease. Pregnancy treatment follows obstetric guidance and gestation; childhood dosing is weight- and age-specific. Severe haemolysis may need urgent cause-specific therapy and transfusion support. Define a measurable follow-up plan using symptoms, haemoglobin, reticulocyte response and replenishment of deficient stores rather than declaring success after one improved value.
Prescribing Information
Prescribe the elemental amount and named formulation, because salt mass and elemental iron are not interchangeable. Oral iron commonly causes nausea, abdominal discomfort, constipation, diarrhoea and dark stools; counselling and a tolerable schedule improve adherence. Food may reduce absorption, while an empty-stomach regimen may worsen adverse effects. Alternate-day or lower-frequency strategies can be useful in selected stable patients, but pregnancy, childhood, severe deficiency and local programme regimens require their own guidance. Failure should trigger reassessment, not endless dose escalation.
Intravenous iron products differ in maximum single dose, dilution, infusion rate and risk profile. Confirm the diagnosis and calculated deficit, check prior reactions, use a setting able to recognise and manage hypersensitivity, and avoid confusing transient infusion reactions with anaphylaxis. Hypophosphataemia is formulation-associated and clinically relevant after repeated exposure. Iron overload, active uncontrolled infection and uncertain anaemia require specialist judgement rather than reflex infusion.
Vitamin B12 route and loading schedule depend on cause, severity, neurological involvement and product availability; malabsorption and pernicious anaemia usually need durable replacement planning. Folate can improve the blood count while neurological B12 injury progresses, so exclude or cover B12 deficiency first. Erythropoiesis-stimulating agents are reserved for defined settings such as selected chronic kidney disease or cancer pathways and can increase thrombotic risk; iron status and treatment targets need specialist monitoring. Red cells, platelets, plasma and cryoprecipitate are prescribed as distinct components for clinical indications. Every transfusion requires identity checks, compatibility practice, consent where possible and monitoring for haemolytic, allergic, febrile, circulatory, lung and infectious complications.
When to Refer
Use emergency referral for haemodynamic instability, ongoing major bleeding, syncope with poor perfusion, chest pain or heart failure attributed to anaemia, rapidly falling haemoglobin, suspected severe haemolysis, sickle crisis, transfusion reaction, or pregnancy with bleeding or cardiorespiratory compromise. Pancytopenia with fever or bleeding, blasts, schistocytes with thrombocytopenia, severe neurological findings or possible aplastic crisis also requires same-day specialist assessment. Resuscitation and referral occur together; an unstable patient should not travel without an accepting service, appropriate escort and blood capability.
Refer to haematology for unexplained or multifactorial anaemia, persistent macrocytosis, haemolysis, haemoglobinopathy, abnormal smear, additional cytopenias, suspected marrow disease, recurrent transfusion need or failure of a documented replacement trial. Gastroenterology referral is important for adult iron deficiency with alarm symptoms or unexplained gastrointestinal loss; urgency depends on age, sex, severity, symptoms and cancer risk. Gynaecology evaluates heavy menstrual or structural uterine bleeding. Nephrology, rheumatology, infectious disease or oncology input follows the suspected mechanism.
Children with severe anaemia, growth failure, haemoglobinopathy, recurrent haemolysis or unclear cytopenia need paediatric expertise. Pregnant patients need obstetric ownership with haematology when severe, refractory or non-nutritional. A useful referral includes serial counts, indices, reticulocytes, smear interpretation, iron and vitamin results, renal and liver tests, bleeding and medication history, prior replacement, transfusions and response. When advanced tests are unavailable locally, escalate on the clinical syndrome rather than delaying until every investigation is complete.
Red Flags
Red flags for inadequate oxygen delivery include hypotension, narrow pulse pressure, cool peripheries, altered consciousness, syncope, persistent tachycardia, severe breathlessness, pulmonary oedema, chest pain, ischaemic ECG change, rising lactate or rapidly deteriorating exercise tolerance. In acute bleeding, an initially normal haemoglobin does not exclude major loss because equilibration takes time. Serial physiology, quantified loss and repeated counts are more informative than false reassurance from the first sample.
Evidence of rapid destruction includes new jaundice, dark urine, back or abdominal pain, fever after transfusion, falling haemoglobin, reticulocytosis and haemolysis markers. Schistocytes with thrombocytopenia, neurological change, renal injury, fever or pregnancy complications can indicate thrombotic microangiopathy or DIC; do not wait for a complete textbook constellation. Bite-cell or blister-cell haemolysis after oxidant exposure, severe malaria, autoimmune haemolysis and delayed transfusion reactions each need a distinct urgent pathway.
Marrow red flags include pancytopenia, circulating blasts, severe neutropenia, unexplained bruising, recurrent infection, bone pain, lymphadenopathy, splenomegaly and constitutional weight loss. Vitamin B12-related gait disturbance, weakness, sensory loss, cognitive change or visual symptoms deserve prompt treatment and neurological assessment even when macrocytosis is absent. Pregnancy with severe symptoms, fetal concern or bleeding, and a child with lethargy, tachypnoea, poor feeding, heart failure or malaria danger signs require urgent age-specific care. A laboratory result incompatible with the patient should be repeated, but clinical instability is treated while confirmation proceeds.
Indian Clinical Context
India needs both population prevention and individual diagnosis. Anemia Mukt Bharat uses a life-course strategy across children, adolescents, women of reproductive age, pregnancy and lactation, combining supplementation, deworming, testing and treatment, behaviour change and attention to non-nutritional causes. Programme prophylaxis is not the same as treatment of a symptomatic patient. A person already anaemic still needs mechanism assessment, adherence and response monitoring, and escalation when the expected improvement does not occur.
NFHS-5 demonstrates very high measured prevalence, but survey haemoglobin cannot establish that iron deficiency caused each case. Diet and iron bioavailability, heavy menstrual bleeding, closely spaced pregnancy, intestinal parasites, malaria in endemic areas, tuberculosis, chronic inflammation, kidney disease and haemoglobinopathies vary by state and community. Empirical iron can delay diagnosis of thalassaemia, B12 deficiency, gastrointestinal loss or marrow disease. Family and regional history should guide haemoglobin testing respectfully, without assuming caste or ethnicity proves a genotype.
Laboratory access is uneven. A district pathway can still start with a reliable CBC, smear, reticulocyte count and ferritin, then refer for haemoglobin analysis, endoscopy, autoimmune tests or marrow examination. Ferritin interpretation should acknowledge infection and inflammation; reticulocyte and smear quality depend on specimen timing and expertise. Transfusion access likewise varies: notify the blood centre early, use component therapy and patient-blood-management principles, and avoid preventable transfusion for a stable correctable deficiency. Document prior transfusions because alloantibodies complicate future compatibility, especially for thalassaemia, sickle disorders and pregnancy. Follow-up plans must account for travel, cost, medicine supply, diet and who will review the repeat count.
NMC Competency Mapping
The NMC CBME Curriculum 2024 provides direct pathology anchors in Topic 14. PA14.1 addresses iron metabolism; PA14.2 addresses the aetiology, investigations and differential diagnosis of microcytic hypochromic anaemia; PA14.3 addresses recognition and description of the peripheral smear. The Medicine IM9 anaemia module extends this foundation to clinical assessment and management. Blood-bank competencies PA21.1 to PA21.6 support rational component use, compatibility and recognition of transfusion reactions. Formal teaching should confirm wording against the institution's current curriculum ledger.
A graduating learner should be able to assess stability, take a bleeding and nutritional history, interpret haemoglobin against age and physiological state, and integrate MCV, RDW, reticulocytes and smear. They should distinguish loss, destruction and impaired production; plan iron, B12, folate, haemolysis and renal testing; and recognise when haemoglobin analysis or marrow assessment is needed. They should explain why ferritin behaves as an acute-phase reactant and why anaemia is not synonymous with iron deficiency.
Integration spans physiology of erythropoiesis, pathology of red-cell disorders, pharmacology of replacement, medicine, paediatrics, obstetrics, community medicine and transfusion practice. Suitable assessments include a pregnant patient with microcytosis, a child with severe pallor and splenomegaly, an older adult with iron deficiency and weight loss, macrocytosis with neuropathy, or anaemia with schistocytes and thrombocytopenia. Students should state initial stabilisation, investigations, referral and safety-netting. Curriculum knowledge does not authorise independent transfusion, intravenous iron, paediatric dosing, endoscopy or marrow procedures.
Key Exam Pearls for NEET PG
Start with physiology: anaemia is a haemoglobin finding; classify it by MCV and by marrow response. The corrected reticulocyte response is low or inappropriate in production failure and rises with blood loss, haemolysis or recovery when marrow reserve and substrates are adequate. A normal MCV can conceal combined iron and B12 or folate deficiency. RDW can suggest mixed or evolving populations but is not a diagnosis. Always inspect the other cell lines and the smear.
Microcytosis suggests iron deficiency, thalassaemia, inflammation, sideroblastic disease or lead toxicity. Low ferritin supports iron depletion; inflammation can raise ferritin and obscure deficiency. Thalassaemia trait often has disproportionate microcytosis with a preserved red-cell count, but confirm with iron assessment and haemoglobin analysis. Macro-ovalocytes and hypersegmented neutrophils suggest megaloblastic change; vitamin B12 deficiency may cause neurological disease without striking macrocytosis. Do not give folate alone when B12 deficiency is plausible.
Haemolysis is a pattern: reticulocytosis, unconjugated bilirubin, raised LDH, reduced haptoglobin and characteristic smear findings, interpreted together. Spherocytes occur in immune haemolysis and membrane disease; schistocytes suggest mechanical fragmentation or microangiopathy. A positive direct antiglobulin test supports immune coating but requires clinical correlation. Pancytopenia shifts attention to marrow failure, infiltration, megaloblastic disease, hypersplenism and infection.
In acute haemorrhage, haemoglobin may initially underestimate severity; resuscitate physiology and control the source. Transfusion thresholds from stable populations are not shock rules. For India, remember that NFHS prevalence is not an aetiological diagnosis, and programme iron does not cancel investigation of non-response, gastrointestinal loss, haemoglobinopathy or marrow disease.
Frequently Asked Questions
Does a low haemoglobin automatically mean iron deficiency anaemia?
No. Iron deficiency is common, but anaemia can result from blood loss, inflammation, kidney disease, vitamin B12 or folate deficiency, haemolysis, haemoglobinopathy, infection, medicines or marrow disease. Use MCV, reticulocyte response, smear and cause-directed tests. Ferritin helps assess iron stores but can rise during inflammation, so one apparently normal value may not settle the question.
Which initial tests give the most useful structure to an anaemia work-up?
Begin with a verified complete blood count including indices and the other cell lines, a peripheral smear and a reticulocyte count. These classify morphology and marrow response. Add ferritin and other iron indices, vitamin B12 or folate, haemolysis studies, renal, liver, thyroid and inflammation tests according to the phenotype. Bleeding evaluation, haemoglobin analysis, endoscopy or marrow examination should answer a specific clinical question.
When is blood transfusion needed for anaemia?
Transfusion is considered for inadequate oxygen delivery, haemodynamic compromise, ongoing major loss or severe symptoms after considering the whole clinical context. Many stable patients can follow a restrictive strategy, but no single haemoglobin threshold safely covers shock, myocardial ischaemia, pregnancy, childhood or major comorbidity. Transfusion does not treat the underlying iron or vitamin deficit and should be followed by cause-specific therapy.
Why might haemoglobin fail to improve after iron treatment?
Common explanations include poor adherence because of adverse effects, an incorrect elemental dose, continued blood loss, malabsorption, inflammation, an alternative or mixed diagnosis, and insufficient follow-up time. Confirm what product was actually taken, reassess ferritin and the reticulocyte or haemoglobin response, and investigate bleeding or systemic disease. Repeated empirical iron without a response is a reason to revisit the diagnosis, not simply to continue indefinitely.
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