Anemias for NEET PG — Classification and Diagnosis 2026

Version 1.0 — Published March 2026

Anemia is defined as a reduction in hemoglobin concentration below the normal range for age and sex — below 13 g/dL in adult males and below 12 g/dL in adult females (WHO criteria). It is not a diagnosis but a finding that demands systematic investigation. In NEET PG, anemia appears across medicine, pathology, pediatrics, and obstetrics — making it one of the highest-yield cross-subject topics. The student who builds a reliable MCV-based diagnostic algorithm and memorizes the key peripheral smear findings will capture marks across at least three subjects.

This guide covers every testable anemia subtype with the lab profiles and smear findings that NBE tests as image-based and clinical vignette questions. Pair this with MCQ practice on the Medicine subject hub and cross-reference high-yield pathology topics for the histopathology angle.

MCV-based classification of anemia

MCV-based classification is the systematic approach to anemia using mean corpuscular volume as the primary sorting criterion — and it is the framework that NEET PG expects you to apply in every anemia vignette.

The diagnostic algorithm in 4 steps:

1. Check MCV → categorize as micro/normo/macrocytic
2. Check reticulocyte count → production defect (<2%) vs destruction/loss (>2%)
3. For microcytic: iron studies (serum iron, TIBC, ferritin, transferrin saturation)
4. For macrocytic: B12, folate levels, peripheral smear for hypersegmented neutrophils

Iron deficiency anemia

Iron deficiency anemia (IDA) is the most common cause of anemia worldwide — affecting approximately 1.2 billion people globally (WHO 2021) and 50% of Indian women of reproductive age (NFHS-5, 2019-2021).

Stages of iron deficiency

Iron depletion progresses through three stages — and NEET PG tests the lab profile at each stage:

Key lab interpretation:

• Ferritin is the MOST SPECIFIC single test for iron deficiency (low ferritin = iron deficiency until proven otherwise)
• TIBC is elevated in iron deficiency (the body upregulates transferrin to capture more iron)
• Transferrin saturation <16% confirms iron-deficient erythropoiesis
• Peripheral smear: Microcytic hypochromic cells, pencil cells (elliptocytes), target cells, increased RDW (anisocytosis)

Causes by age group:

• Children: dietary insufficiency, hookworm (Ancylostoma duodenale in India)
• Menstruating women: menorrhagia (most common cause in reproductive-age women)
• Adult males and postmenopausal women: GI blood loss until proven otherwise — ALWAYS investigate for colon cancer

Treatment: Oral ferrous sulfate (200 mg TDS, contains 60 mg elemental iron each). Response: reticulocyte count peaks at 5–10 days. Continue for 3–6 months after hemoglobin normalizes to replenish stores. Parenteral iron (IV iron sucrose, ferric carboxymaltose) for malabsorption, intolerance, or severe anemia.

Megaloblastic anemia

Megaloblastic anemia is a macrocytic anemia caused by impaired DNA synthesis due to B12 or folate deficiency — resulting in nuclear-cytoplasmic asynchrony (nucleus matures slower than cytoplasm) and the characteristic oval macrocytes and hypersegmented neutrophils on peripheral smear.

B12 vs folate deficiency

Critical NBE point: NEVER give folate alone to a patient with B12 deficiency — it corrects the hematological picture but worsens the neurological damage (folate trap hypothesis).

Pernicious anemia:

• Autoimmune destruction of gastric parietal cells → loss of intrinsic factor → B12 malabsorption
• Antibodies: anti-intrinsic factor (most specific), anti-parietal cell (more sensitive)
• Association: autoimmune thyroiditis, vitiligo, type 1 DM
• Increased risk of gastric carcinoma — requires endoscopic surveillance

Peripheral smear findings in megaloblastic anemia

• Oval macrocytes (large, oval-shaped RBCs)
• Hypersegmented neutrophils (≥5 lobes in one neutrophil OR ≥5% neutrophils with 5+ lobes) — pathognomonic
• Anisocytosis and poikilocytosis (elevated RDW)
• Howell-Jolly bodies may be present (nuclear remnants)

Hemolytic anemias

Hemolytic anemia is premature destruction of red blood cells (lifespan <120 days) leading to anemia with compensatory reticulocytosis — characterized by elevated LDH, elevated indirect bilirubin, low haptoglobin, and increased reticulocyte count.

Classification

Key rule: All intrinsic defects are inherited EXCEPT paroxysmal nocturnal hemoglobinuria (PNH), which is an acquired membrane defect (somatic PIGA gene mutation).

Hereditary spherocytosis

Hereditary spherocytosis is the most common inherited hemolytic anemia in northern European populations — caused by defects in RBC membrane proteins (spectrin, ankyrin, band 3, protein 4.2).

• Inheritance: Autosomal dominant (75% of cases)
• Clinical: Jaundice, splenomegaly, pigment gallstones (bilirubin stones in a young patient — classic NEET PG clue)
• Diagnosis: Osmotic fragility test (spherocytes lyse at higher NaCl concentration than normal RBCs), EMA binding test (flow cytometry — gold standard)
• Smear: Spherocytes (small, round, dense, no central pallor)
• Treatment: Splenectomy (curative for hemolysis, not the membrane defect). Vaccinate against encapsulated organisms (pneumococcus, meningococcus, H. influenzae) before splenectomy.

G6PD deficiency

G6PD deficiency is the most common enzyme deficiency worldwide — an X-linked recessive disorder affecting approximately 400 million people, with highest prevalence in Africa, Mediterranean, and Southeast Asia.

Mechanism: G6PD catalyzes the first step of the pentose phosphate pathway, generating NADPH to maintain reduced glutathione (protects RBCs from oxidative stress). Deficiency → oxidative damage → hemolysis.

Triggers (the oxidant stress list):

• Drugs: Primaquine, dapsone, nitrofurantoin, sulfonamides, nalidixic acid
• Infections: Most common trigger overall
• Foods: Fava beans (favism — Mediterranean variant)

Smear findings: Heinz bodies (denatured hemoglobin — seen with supravital staining), bite cells (removal of Heinz bodies by splenic macrophages)

Key NBE trap: G6PD levels may be NORMAL during an acute hemolytic episode (because old, deficient cells have already been destroyed — reticulocytes have near-normal G6PD). Repeat the test 2–3 months after the acute episode.

Sickle cell disease

Sickle cell disease is caused by a point mutation in the beta-globin gene (glutamic acid → valine at position 6) producing hemoglobin S (HbS), which polymerizes under low oxygen tension causing RBC sickling.

Clinical features:

• Vaso-occlusive crisis: Bone pain (most common), acute chest syndrome, stroke, priapism, splenic sequestration
• Aplastic crisis: Parvovirus B19 infection → transient red cell aplasia
• Sequestration crisis: Sudden trapping of RBCs in spleen (children) → acute splenic enlargement + hemodynamic collapse
• Functional asplenia by age 5 (autosplenectomy) → susceptibility to encapsulated organisms

Diagnosis: Hemoglobin electrophoresis — HbS >80%, HbF variable, HbA2 normal, HbA absent Smear: Sickle cells, target cells, Howell-Jolly bodies (functional asplenia)

Management:

• Hydroxyurea (increases HbF, reduces crises by 50%)
• Penicillin V prophylaxis from 2 months to 5 years
• Pneumococcal, meningococcal, Hib vaccines
• Blood transfusion for acute chest syndrome, stroke prevention
• Bone marrow transplant — only curative option

Thalassemia

Thalassemia is a quantitative defect in globin chain synthesis — reduced alpha chains (alpha-thalassemia) or reduced beta chains (beta-thalassemia) — leading to ineffective erythropoiesis and hemolysis.

Beta-thalassemia classification:

Beta-thal major clinical features:

• Severe anemia presenting at 6 months (when fetal hemoglobin declines)
• Hepatosplenomegaly (extramedullary hematopoiesis)
• Skeletal changes: crew-cut appearance on skull X-ray, chipmunk facies (maxillary hyperplasia), hair-on-end appearance
• Iron overload from transfusions → hemochromatosis (cardiac, hepatic, endocrine)

Alpha-thalassemia:

Iron deficiency vs thalassemia trait — the classic NEET PG differentiation:

Aplastic anemia

Aplastic anemia is bone marrow failure resulting in pancytopenia (anemia + leukopenia + thrombocytopenia) with a hypocellular bone marrow — a hematological emergency when severe.

Causes:

• Idiopathic: 50–65% of cases (likely immune-mediated T-cell destruction of stem cells)
• Drugs: Chloramphenicol (dose-independent idiosyncratic reaction — most tested drug cause), benzene, gold, carbamazepine, phenytoin
• Infections: Parvovirus B19 (pure red cell aplasia), hepatitis (seronegative hepatitis → aplastic anemia), EBV, HIV
• Radiation
• Inherited: Fanconi anemia (autosomal recessive, associated with short stature, cafe-au-lait spots, absent thumbs, horseshoe kidney — DNA repair defect)

Diagnostic criteria for severe aplastic anemia (2 of 3):

• Neutrophils <500/mcL
• Platelets <20,000/mcL
• Reticulocytes <1% (corrected)

Bone marrow biopsy: Hypocellular (<25% cellularity) with fat replacement — this distinguishes aplastic anemia from leukemia or myelodysplasia (both hypercellular).

Treatment:

• Age <40 + matched sibling donor: Allogeneic hematopoietic stem cell transplant (treatment of choice)
• Age >40 or no donor: Immunosuppressive therapy (ATG + cyclosporine + eltrombopag)
• Supportive: transfusions (irradiated, leukoreduced), antibiotics for febrile neutropenia

Anemia of chronic disease

Anemia of chronic disease (ACD) is the second most common anemia worldwide — a normocytic (sometimes microcytic) anemia occurring in the setting of chronic infection, inflammation, autoimmune disease, or malignancy, mediated by hepcidin.

Pathophysiology:

1. Chronic inflammation → IL-6 → hepatic hepcidin production
2. Hepcidin binds ferroportin on enterocytes and macrophages → ferroportin degradation
3. Iron is trapped inside cells (cannot be exported to plasma)
4. Result: low serum iron, low transferrin saturation, BUT normal or elevated ferritin (iron is present but sequestered)

The critical lab comparison — ACD vs IDA:

NBE tip: When serum iron is low in BOTH conditions, ferritin is the single best differentiator. Low ferritin = iron deficiency. High ferritin with low iron = chronic disease.

Treatment: Treat the underlying disease. EPO (erythropoietin) for moderate-severe ACD in CKD or cancer. Iron supplementation is generally NOT useful (iron is sequestered, not deficient).

Peripheral smear findings — the comparison table

Peripheral smear identification is among the most directly testable topics in pathology and medicine — NBE frequently shows an image or describes findings and asks for the diagnosis.

Approach to a patient with anemia — the diagnostic algorithm

The systematic approach to anemia diagnosis is a clinical algorithm that starts with MCV, adds reticulocyte count, and uses specific tests to reach the final diagnosis — this is the framework NBE expects in every anemia vignette.

Step 1: Confirm anemia and classify by MCV

• Hb <13 g/dL (males) or <12 g/dL (females) → anemia confirmed
• Check MCV → microcytic / normocytic / macrocytic

Step 2: Check reticulocyte count

• Corrected reticulocyte count = (patient Hct / normal Hct) x reticulocyte %
• Reticulocyte production index (RPI) = corrected count / maturation factor
• RPI >2 → adequate marrow response → hemolysis or blood loss
• RPI <2 → inadequate response → production defect

Step 3: For microcytic anemia → Iron studies

• Low ferritin → Iron deficiency → Find the cause (GI blood loss in adult males)
• Normal/high ferritin + elevated HbA2 → Beta-thalassemia trait
• Ring sideroblasts on marrow → Sideroblastic anemia

Step 4: For normocytic anemia → Reticulocyte-guided

• High reticulocytes + LDH high + haptoglobin low → Hemolysis → Direct Coombs test (positive = autoimmune, negative = intrinsic/mechanical)
• Low reticulocytes + pancytopenia → Bone marrow biopsy (aplastic anemia vs infiltrative process)
• Low reticulocytes + isolated anemia → Consider CKD (EPO level), chronic disease

Step 5: For macrocytic anemia → B12, folate, peripheral smear

• Hypersegmented neutrophils → Megaloblastic → Check B12 and folate, methylmalonic acid
• No hypersegmented neutrophils → Non-megaloblastic → Consider liver disease, hypothyroidism, MDS, reticulocytosis

Sources and references

1. Harrison's Principles of Internal Medicine, 21st Edition (Loscalzo et al., 2022) — Chapters on anemia, iron metabolism, and hemolytic disorders.
2. Robbins and Cotran Pathologic Basis of Disease, 10th Edition (Kumar et al., 2021) — RBC disorders, hemoglobinopathies, and bone marrow pathology.
3. Williams Hematology, 10th Edition (Kaushansky et al., 2021) — comprehensive hematology reference for iron metabolism and hemolysis.
4. WHO — Worldwide prevalence of anaemia 1993-2005 (updated 2021) — global epidemiological data on anemia burden.
5. NFHS-5 (National Family Health Survey, 2019-2021) — Indian-specific anemia prevalence data.

Frequently asked questions

How many anemia questions appear in NEET PG?

Anemia-related questions contribute 4-6 questions per NEET PG paper, spanning medicine, pathology, and pediatrics. Iron deficiency anemia lab profiles, peripheral smear findings, and hemolytic anemia differentiation are the three most predictable subtopics across 2019-2025 papers.

What is the most common cause of anemia worldwide?

Iron deficiency anemia is the most common cause of anemia globally and in India, affecting approximately 50% of Indian women of reproductive age (NFHS-5, 2019-2021). It accounts for 60-80% of all anemia cases and presents as microcytic hypochromic anemia with low serum ferritin.

How do I differentiate iron deficiency from thalassemia trait on labs?

Iron deficiency shows low serum iron, high TIBC, low ferritin, and low transferrin saturation. Thalassemia trait shows normal or high serum iron, normal TIBC, normal or high ferritin, and elevated HbA2 on HPLC. The Mentzer index (MCV/RBC count) helps: below 13 suggests thalassemia trait, above 13 suggests iron deficiency.

What causes megaloblastic anemia?

Vitamin B12 deficiency (pernicious anemia, strict vegetarianism, ileal disease, Diphyllobothrium latum) and folate deficiency (poor diet, alcoholism, pregnancy, methotrexate, phenytoin) cause megaloblastic anemia. Both show macrocytic anemia with hypersegmented neutrophils on smear, but only B12 deficiency causes neurological manifestations (subacute combined degeneration).

What is the most common inherited hemolytic anemia?

Hereditary spherocytosis is the most common inherited hemolytic anemia in northern European populations. In India and Southeast Asia, thalassemia and G6PD deficiency are more prevalent. G6PD deficiency is the most common enzyme deficiency worldwide, affecting approximately 400 million people globally.

How do I approach an anemia question in NEET PG?

Start with MCV: microcytic (below 80 fL) narrows to iron deficiency, thalassemia, sideroblastic, chronic disease. Normocytic (80-100 fL) points to acute blood loss, chronic disease, hemolysis, early deficiency. Macrocytic (above 100 fL) suggests B12/folate deficiency, liver disease, hypothyroidism, myelodysplasia. Then use reticulocyte count to separate production defects from destruction.

What peripheral smear finding is pathognomonic for DIC?

Schistocytes (fragmented red cells or helmet cells) on peripheral smear in the setting of thrombocytopenia, prolonged PT/aPTT, elevated D-dimer, and low fibrinogen is the classic pattern for DIC. Schistocytes alone can also indicate TTP, HUS, or mechanical heart valve hemolysis — clinical context differentiates.

What is the treatment for severe aplastic anemia in a young patient?

Allogeneic hematopoietic stem cell transplant from an HLA-matched sibling donor is the treatment of choice for severe aplastic anemia in patients below 40 years. If no matched donor is available, immunosuppressive therapy with anti-thymocyte globulin plus cyclosporine is the alternative. Eltrombopag (TPO receptor agonist) is added to first-line IST in current protocols.

What is the anemia of chronic disease mechanism?

Anemia of chronic disease is mediated by hepcidin, an acute-phase reactant produced by the liver in response to IL-6. Hepcidin blocks ferroportin on enterocytes and macrophages, trapping iron intracellularly. This results in low serum iron but high or normal ferritin — the key lab distinguisher from iron deficiency anemia where ferritin is low.

Which anemia shows target cells on peripheral smear?

Target cells (codocytes) appear in thalassemia, iron deficiency anemia, liver disease, hemoglobin C disease, and post-splenectomy states. The mnemonic HALT helps: HbC disease, Asplenia, Liver disease, Thalassemia. In NEET PG vignettes, target cells with microcytosis most commonly point to thalassemia.

Build your anemia pattern recognition by practicing hematology MCQs daily. The smear findings and lab profiles you drill now become automatic on exam day.

Start practicing hematology MCQs free →

Check our pricing plans for unlimited access to 19 subjects, and build a personalized study plan that covers the entire hematology syllabus.

---

Written by: NEETPGAI Editorial Team Reviewed by: Pending SME Review Last reviewed: March 2026

This article is reviewed by qualified medical professionals for clinical accuracy and exam relevance. For corrections or updates, contact the editorial team.