---

Anemia — Complete Diagnostic Approach (Stepwise)

---

Physiologic Basis

---

Definition: Normal Hemoglobin/Hematocrit Values

---

Step 1 — History

• Previous episodes of anemia, prior iron pills or transfusions
• Family history (hemoglobinopathies, hereditary spherocytosis)
• Menstrual history: duration of periods, number of pads/tampons, large clots
• Blood donation
• Dietary history (vegetarian/vegan → B12 risk; poor diet → folate risk)
• Alcohol use, liver disease, hypothyroidism
• Symptoms pointing to underlying cause: diarrhea (celiac, IBD), bone pain (myeloma), weight loss (malignancy), neurological symptoms (B12 deficiency)
• Medications (chemotherapy, methotrexate, antiseizure drugs, ACE inhibitors, NSAIDs → GI blood loss)
• Geography/ethnicity (sickle cell, thalassemia in relevant populations)

---

Step 2 — Physical Examination

• Consequences of anemia: pallor of mucosa/conjunctiva, resting tachycardia, cardiac flow murmur, dyspnea
• Clues to cause:
  • Splenomegaly → hemolysis, lymphoma, portal hypertension
  • Lymphadenopathy → lymphoma, leukemia
  • Hepatomegaly/jaundice → hemolytic anemia, liver disease
  • Glossitis, angular cheilitis, koilonychia → iron deficiency
  • Neurologic signs (subacute combined degeneration) → B12 deficiency
  • Petechiae/bleeding → aplastic anemia, thrombocytopenia
  • Rectal exam/occult blood → GI blood loss

---

Step 3 — Initial Laboratory Work-Up

Complete Blood Count (CBC) with Differential

Reticulocyte Count — The Critical Branching Point

• Elevated ARC (>100,000/μL) → Bone marrow is responding → anemia due to increased loss or destruction (bleeding or hemolysis)
• Low/normal ARC (<50,000/μL) → Bone marrow is failing to respond → anemia due to impaired production (hypoproliferative)

The reticulocyte production index (RPI) = [reticulocyte % × Hct/45] / maturation factor. An RPI <2 indicates hypoproliferation; RPI >3 indicates hyperproliferation.

---

Step 4 — Peripheral Blood Smear (MANDATORY)

"A review of the blood smear is a crucial part of any evaluation for anemia as changes in red cell morphology can point to specific causes of anemia." — Harrison's 22E

Normal Blood Smear (Reference)

---

Key Red Cell Morphology and Diagnostic Significance

---

Step 5 — MCV-Based Classification and Targeted Workup

5A — Microcytic Anemia (MCV < 80 fL)

Peripheral Smear: Severe Iron Deficiency Anemia

Key distinguishing clue: RDW is high in iron deficiency (anisocytosis) but low in thalassemia (uniform microcytosis). — Harrison's 22E

Ferritin <30 μg/L = depleted iron stores. Ferritin >200 μg/L = some tissue stores remain. However, ferritin is an acute-phase reactant — it may be falsely elevated in inflammation even with concurrent iron deficiency.

---

5B — Macrocytic Anemia (MCV > 100 fL)

Oval Macrocytes (Megaloblastic pattern)

• Causes: Vitamin B12 deficiency · Folate deficiency · Chemotherapy agents (hydroxyurea, methotrexate) · Myelodysplastic syndrome (MDS)

Round Macrocytes (Non-megaloblastic)

• Causes: Alcohol use · Liver disease · Hypothyroidism · Reticulocytosis · Dysproteinemia · Smoking · Hypoxia

Peripheral Smear + Bone Marrow: Severe Megaloblastic Anemia

1. Blood smear — oval vs. round macrocytes? Hypersegmented neutrophils?
2. If megaloblastic pattern: Serum B12 + serum folate / RBC folate
3. If B12 low: anti-intrinsic factor antibodies (pernicious anemia), Schilling test if needed
4. If B12/folate normal with macro-ovalocytes: bone marrow biopsy (suspect MDS)
5. If round macrocytes: check TSH, LFTs, alcohol history

---

5C — Normocytic Anemia (MCV 80–100 fL)

• Aplastic anemia · Pure red cell aplasia
• Renal disease (EPO deficiency)
• Anemia of inflammation/chronic disease
• Endocrinopathies (hypothyroidism, Addison's)
• Marrow infiltration (myeloma, metastases, granulomas)
• Stem cell defects (leukemia, MDS)
• Acute blood loss/early iron deficiency

1. Reticulocyte count (see Step 4 above)
2. Renal function (Cr/eGFR), EPO level
3. TSH, cortisol (endocrine causes)
4. Serum protein electrophoresis (SPEP) for myeloma
5. LDH, haptoglobin, bilirubin (if hemolysis suspected)
6. Consider bone marrow exam if no clear cause found

---

Step 6 — Reticulocyte-Guided Mechanistic Workup

6A — High Reticulocyte Count → Hemolysis / Blood Loss

Hemolysis Workup:

Autoimmune Hemolytic Anemia — Peripheral Smear

Sickle Cell Disease — Peripheral Smear

---

6B — Low Reticulocyte Count → Hypoproliferative (Underproduction)

"At least 75% of all cases of anemia are hypoproliferative in nature." — Harrison's 22E

Sub-classification by mechanism:

Anemia of Chronic Inflammation — Mechanism

1. Iron absorption from the gut
2. Iron release from macrophages/stores → Functional iron deficiency despite normal/high stores. EPO levels are also suppressed by cytokines. Laboratory: normocytic or mild microcytic anemia; ferritin high (acute-phase reactant); serum iron low; TIBC low (distinguishes from true iron deficiency where TIBC is high). — Harrison's 22E, Robbins & Kumar

---

Step 7 — Bone Marrow Examination

1. Unexplained severe anemia
2. Abnormal peripheral blood smear morphology suggesting marrow pathology
3. Suspected aplastic anemia, MDS, or leukemia
4. Circulating nucleated red blood cells
5. Myelophthisic picture (teardrop cells + leukoerythroblastosis)
6. Staging of lymphoma or certain malignancies
7. Macro-ovalocytes with normal B12/folate (suspect MDS)
8. Marrow infiltration suspected (myeloma, metastases, granulomas)

---

Step 8 — Additional Targeted Tests by Clinical Context

---

Summary Algorithm

Hemoglobin low?
       │
       ▼
History + Physical → Severity, Symptoms, Clues to Cause
       │
       ▼
CBC + Reticulocyte Count + Peripheral Blood Smear
       │
       ├── Retic ↑ (>100K) ─── Bleeding? ── YES → GI workup, imaging
       │                         │
       │                         NO → Hemolysis workup:
       │                              LDH ↑, Haptoglobin ↓, Indirect bili ↑
       │                              DAT (Coombs), smear morphology
       │                              G6PD, Hb electrophoresis, PNH screen
       │
       └── Retic ↓ / normal ── MCV?
                                │
                    ┌───────────┼──────────────┐
                    ▼           ▼              ▼
               Microcytic   Normocytic     Macrocytic
               (MCV <80)   (MCV 80–100)   (MCV >100)
                    │           │              │
              Ferritin +    Renal Fn,      Smear →
              Serum Fe +    EPO level,     Oval macros?
              TIBC +        TSH, SPEP,     → B12/Folate
              Hb electro    BM if needed   Round macros?
              RDW                          → Alcohol/Liver/
              (↑ IDA,                        Thyroid
              ↓ Thal)                      Normal B12/folate
                                           + oval macros?
                                           → BM (MDS)

---

Comparison: Iron Deficiency vs. Anemia of Inflammation (Common Clinical Dilemma)

---

Macrocytic Anemia: B12 vs. Folate vs. MDS

---

Severity Classification

---

Key Points

1. Reticulocyte count is the single most important test after the CBC — it divides anemia into hyperproliferative (hemolysis/bleeding) vs. hypoproliferative (underproduction).
2. Peripheral blood smear is mandatory and often diagnostic without further testing.
3. MCV classifies by morphology and drives targeted testing in hypoproliferative anemia.
4. RDW distinguishes iron deficiency (high, anisocytosis) from thalassemia (low, uniform cells).
5. Ferritin is an acute-phase reactant — it can be normal or high in combined iron deficiency + inflammation.
6. Hepcidin is the master iron regulator — elevated in anemia of inflammation; suppressed in iron deficiency.
7. Bone marrow biopsy is reserved for unexplained anemia with myelophthisic features, pancytopenia, suspected malignancy, or when initial workup is unrevealing.
8. At least 75% of all anemia is hypoproliferative; the most common cause globally is iron deficiency.

---

---

---

• Header — title + normal Hb reference values by population
• Steps 1–2 — History & Physical Exam side-by-side
• Step 3 — CBC indices quick-reference bar
• Step 4 — Reticulocyte count master branch diamond (High → Hemolysis/Bleeding | Low → Underproduction)
• Step 5 — MCV 3-column classification (Microcytic / Normocytic / Macrocytic) with causes and tests
• Step 6 — Iron studies differential table (IDA vs ACD vs Thal vs Sideroblastic) with key highlights
• Step 7 — Peripheral smear morphology tiles (8 RBC abnormalities → diagnoses)
• Step 8 — Hemolysis workup grid (LDH, haptoglobin, DAT, G6PD, PNH screen)
• Step 9 — B12 vs Folate vs MDS differential table
• Step 10 — Diagnostic algorithm flowchart + Bone marrow indications
• Footer — Severity band + 8 high-yield pearls