Anemia Study Guide

📖 Core Concepts Anemia – a reduction in the blood’s capacity to carry oxygen, caused by low RBC count, low hemoglobin, or abnormal hemoglobin. Severity thresholds (adults) Mild: Hb 110–<130 g/L (men), 110–<120 g/L (women) Moderate: Hb 80–<110 g/L Severe: Hb < 80 g/L Red‑cell size categories (by MCV) Microcytic: MCV < 80 fL Normocytic: MCV = 80–100 fL Macrocytic: MCV > 100 fL Major etiologic groups Blood loss (chronic or acute) Impaired production – iron, folate, B12 deficiency; thalassemia; marrow failure Increased destruction – hemolysis (intrinsic vs. extrinsic) Dilutional (hypervolemic) anemia Key lab tools – CBC with indices, reticulocyte count/production index, iron studies, vitamin B12/folate levels, peripheral smear, Mentzer index. Treatment principle – address the underlying cause (replace nutrients, stop bleeding, manage hemolysis, support erythropoiesis, or transfuse when needed). --- 📌 Must Remember Hemoglobin cut‑offs (WHO): < 130 g/L (men), < 120 g/L (non‑pregnant women), < 105–110 g/L (pregnant women). Iron‑deficiency anemia (IDA) is the single most common cause worldwide (≈ 1 billion people). Mentzer index: $$\text{Mentzer} = \frac{\text{MCV (fL)}}{\text{RBC count }(10^{12}/\text{L})}$$ > 13 → iron deficiency < 13 → thalassemia trait Reticulocyte Production Index (RPI) > 2 = adequate marrow response; < 2 = underproduction. Transfusion thresholds – generally Hb < 60–80 g/L (6–8 g/dL); higher (70–80 g/L) if CAD present. Oral iron dose – 60–120 mg elemental iron daily; Vitamin C enhances absorption, food reduces it. B12 replacement – IM cyanocobalamin (initial daily → weekly → monthly). ESAs are reserved for CKD or chemotherapy‑induced anemia when Hb < 10 g/dL and iron stores are sufficient. --- 🔄 Key Processes Initial anemia work‑up Measure Hb → confirm anemia. Obtain CBC with MCV → classify size. Review clinical history (bleeding, diet, chronic disease). Order reticulocyte count → assess marrow response. Perform iron studies (Ferritin, serum iron, TIBC, transferrin saturation). Add B12/folate levels if macrocytic or neurologic signs. Examine peripheral smear for morphology (microcytosis, schistocytes, hypersegmented neutrophils). Iron‑deficiency management algorithm Confirm low ferritin < 30 ng/mL (or low transferrin saturation). Start oral iron + Vitamin C; counsel on side‑effects. Re‑check Hb in 4 weeks; if no rise or intolerance → IV iron. Reserve transfusion for Hb < 60 g/L or symptomatic instability. B12 deficiency treatment pathway Diagnose via low serum B12 + clinical neuro findings. Give IM cyanocobalamin 1000 µg daily × 1‑2 weeks → weekly → monthly. Monitor neurologic recovery (usually 1‑2 weeks) and Hb rise (2‑3 weeks). Hemolysis evaluation Labs: LDH ↑, haptoglobin ↓, indirect bilirubin ↑, reticulocytosis. Smear: schistocytes, spherocytes, sickle cells. Distinguish intrinsic (membrane/enzyme defects) vs. extrinsic (autoimmune, mechanical, infection). --- 🔍 Key Comparisons Iron‑deficiency anemia vs. Thalassemia trait MCV: both microcytic. RBC count: ↑ in thalassemia, ↓ in iron deficiency. Mentzer index: > 13 (IDA) vs. < 13 (thalassemia). Vitamin B12 deficiency vs. Folate deficiency Neurologic signs: present in B12, absent in folate. Methylmalonic acid: ↑ in B12, normal in folate. Acute vs. Chronic anemia presentation Acute: sudden faintness, confusion, tachycardia, sweating. Chronic: fatigue, dyspnea on exertion, pallor, pica (iron‑deficiency). Normocytic anemia causes Acute blood loss, anemia of chronic disease, hemolysis, aplastic anemia – all present with normal MCV. --- ⚠️ Common Misunderstandings “All microcytic anemia = iron deficiency.” Correction: Thalassemia, anemia of chronic disease, sideroblastic anemia can also be microcytic. Use RBC count & Mentzer index. “Ferritin is always low in iron deficiency.” Correction: Ferritin is an acute‑phase reactant; it can be normal/elevated in inflammation despite iron deficiency. Check transferrin saturation. “Oral iron is safe for everyone.” Correction: Contraindicated or less effective in malabsorption, inflammatory bowel disease, or when rapid repletion is needed. “Transfusion is the quickest fix for any anemia.” Correction: Transfusion carries risks; reserve for symptomatic or severe (< 60 g/L) cases. --- 🧠 Mental Models / Intuition “Size → Mechanism” – Think of MCV as the first clue: Microcytic → iron, thalassemia, sideroblastic, chronic disease. Normocytic → blood loss, hemolysis, chronic disease, marrow failure. Macrocytic → B12/folate deficiency, alcohol, hypothyroidism, marrow dyspoiesis. “Retic count is the marrow’s report card.” High → marrow is trying (hemolysis, blood loss). Low → production problem (nutrient deficiency, marrow failure). “Ferritin = iron store; Transferrin saturation = iron availability.” Low ferritin → true deficiency. Normal/high ferritin + low saturation → anemia of chronic disease. --- 🚩 Exceptions & Edge Cases Anemia of chronic disease can present as normocytic early, becoming microcytic later. Pregnancy physiologic dilution: plasma volume expands > RBC mass → mild normocytic anemia (Hb < 105–110 g/L). High ferritin may mask iron deficiency in inflammatory states; rely on soluble transferrin receptor if available. Parasitic infections (hookworm) cause chronic blood loss → iron deficiency even with adequate diet. --- 📍 When to Use Which Oral vs. IV iron – Use oral first unless patient has intolerance, malabsorption, or needs rapid repletion (pre‑op, severe symptomatic IDA). ESAs – Indicated for CKD or chemotherapy‑related anemia and when iron stores are replete or being repleted (IV iron). Blood transfusion – Choose when Hb < 60 g/L or patient is symptomatic (tachycardia, chest pain, hypotension) despite adequate medical therapy. Peripheral smear – Essential when CBC indices are ambiguous or when hemolysis is suspected. Mentzer index – Use to differentiate iron deficiency from thalassemia in microcytic anemia with available RBC count. --- 👀 Patterns to Recognize Pica + koilonychia → classic for iron‑deficiency anemia. Glossitis + neuro deficits → B12 deficiency. Elevated LDH + low haptoglobin + reticulocytosis → hemolysis. Low ferritin + high TIBC → iron deficiency; normal/high ferritin + low TIBC → anemia of chronic disease. Macrocytosis + hypersegmented neutrophils → megaloblastic (B12/folate) anemia. --- 🗂️ Exam Traps “Ferritin low → iron deficiency” – remember ferritin can be falsely high in inflammation. “All macrocytic anemia needs B12” – folate deficiency produces macrocytosis without neurologic signs. “Transfusion threshold is always 70 g/L” – the threshold varies (60–80 g/L) and is higher in CAD or active bleeding. “Normal MCV rules out iron deficiency” – early iron deficiency may be normocytic; look at ferritin and RBC count. “All hemolysis shows jaundice” – intravascular hemolysis may present primarily with dark urine and elevated LDH, not always visible jaundice. ---