Anemia is defined as a decrease in red blood cell (RBC) mass , hemoglobin (Hb), and/or hematocrit (Hct) below the reference range for age and sex. It reflects a reduced oxygen-carrying capacity of the blood.
Normal Reference Ranges:
| Parameter | Male | Female |
|---|---|---|
| RBC count | 4.5–5.9 x10⁶/µL | 4.1–5.1 x10⁶/µL |
| Hemoglobin | 14.0–17.5 g/dL | 12.3–15.3 g/dL |
| Hematocrit | 43–50% | 36–45% |
Types of Anemia
I. Etiologic Classification
| Etiology | Mechanism |
|---|---|
| Impaired RBC production | Bone marrow failure, nutrient deficiency, chronic disease |
| Increased RBC destruction (hemolysis) | Inherited or acquired defects |
| Blood loss | Acute (e.g., trauma) or chronic (e.g., GI bleeding, menstruation) |
II. Morphologic Classification
Based on Mean Corpuscular Volume (MCV) and Mean Corpuscular Hemoglobin Concentration (MCHC) :
| Morphology | MCV | MCHC | Examples |
|---|---|---|---|
| Macrocytic | > 94 fL | > 31% | Vitamin B12 & folate deficiency, myelodysplastic syndromes |
| Microcytic hypochromic | < 80 fL | < 27% | Iron deficiency, thalassemia |
| Normocytic normochromic | 82–92 fL | > 30% | Aplastic anemia, hemolysis, chronic disease |
Etiologies in Detail
A. Impaired RBC Production
- Bone Marrow Failure
- Aplastic anemia
- Myelophthisis (bone marrow infiltration by fibrosis, leukemia)
- Deficiencies of Essential Factors
- Iron deficiency anemia
- Vitamin B12 deficiency (pernicious anemia)
- Folate deficiency
- Anemia in chronic kidney disease (↓ erythropoietin)
- Reduced Hormonal Stimulation
- Hypothyroidism
- Hypopituitarism
- Anemia of chronic inflammation (e.g., autoimmune disease, malignancy)
B. Excessive RBC Destruction (Hemolytic Anemias)
1. Intracorpuscular Defects (inherited):
- Membrane defects: Hereditary spherocytosis, elliptocytosis
- Enzyme defects: G6PD deficiency
- Hemoglobinopathies: Thalassemia, sickle cell disease
2. Extracorpuscular Defects (acquired):
- Mechanical : MAHA (e.g., DIC, TTP, prosthetic valves)
- Infectious : Malaria, Clostridium perfringens
- Autoimmune : SLE, transfusion reactions
- Hypersplenism
C. Blood Loss
- Acute : Trauma, GI hemorrhage
- Chronic : Menorrhagia, hookworm infestation, GI ulcers
True vs. Pseudo-Anemia
| Type | Description | Example |
|---|---|---|
| True anemia | ↓ RBC mass with normal plasma volume | Nutritional deficiency, hemolysis |
| Pseudo-anemia | Normal RBC mass, ↑ plasma volume (dilutional) | Pregnancy, IV fluid overload, CHF |
Clinical Features of Anemia
Symptoms:
- Fatigue
- Dyspnea on exertion
- Lightheadedness
- Chest pain or worsening angina
Signs:
- Pallor (especially mucous membranes)
- Tachycardia
- Systolic flow murmur
- Orthostatic hypotension
- Ankle edema (in severe cases)
- Tachypnea
- Raised JVP
Workup and Diagnosis
Initial Labs:
- CBC (RBC count, Hgb, Hct, MCV, MCHC)
- Reticulocyte count
- Peripheral blood smear
- Iron studies (serum ferritin, TIBC, transferrin saturation)
- Vitamin B12 and folate levels
- LDH, haptoglobin, bilirubin (for hemolysis)
- Coombs test (if autoimmune hemolysis suspected)
Treatment Principles
Always treat the underlying cause first.
1. Iron Deficiency Anemia
- Oral iron : Ferrous sulfate 325 mg once daily on an empty stomach
- Parenteral iron if oral is not tolerated or ineffective
- Address source of bleeding (e.g., GI lesions, heavy menstruation)
2. Vitamin B12 Deficiency
- IM or SC Vitamin B12 100 mcg injections weekly until corrected, then monthly
3. Folate Deficiency
- Oral folic acid 1 mg/day
4. Anemia of Chronic Disease
- Treat the underlying condition
- Consider erythropoiesis-stimulating agents (ESA) if anemia is symptomatic or severe (e.g., in CKD)
5. Hemolytic Anemia
- Manage triggers (e.g., avoid oxidant drugs in G6PD deficiency)
- Immunosuppressants or transfusion in autoimmune hemolysis
- Splenectomy in hereditary spherocytosis (if severe)
6. Severe or Symptomatic Anemia
- RBC transfusion if Hgb < 7–8 g/dL or symptomatic
- Consider ESA if transfusion is contraindicated or ineffective
High-Yield Pearls
- MCV < 80 = Microcytic → Think Iron Deficiency, Thalassemia
- MCV > 100 = Macrocytic → Think B12/Folate deficiency, drugs
- High Retic Count = Bone marrow is responding (think hemolysis or bleeding)
- Low Retic Count = Bone marrow failure or nutrient deficiency
- TIBC ↑ + Ferritin ↓ = Iron Deficiency Anemia
- Ferritin ↑ + TIBC ↓ = Anemia of Chronic Disease
