Complete Blood Count (CBC) Test

Complete Blood Count (CBC) Test: Disease-Specific Interpretation & Differential Diagnosis (DD)

A Complete Blood Count (CBC) is one of the most fundamental tests in hematology. It provides key insights into a patient’s overall health and aids in diagnosing various hematologic and systemic conditions. Below is a disease-specific interpretation of CBC parameters with relevant values and differentials.

1. Red Blood Cell (RBC) Indices and Anemia Classification

Parameter	Normal Range	Decreased in	Increased in
Hemoglobin (Hb)	Male: 13.8–17.2 g/dL Female: 12.1–15.1 g/dL	Anemia (iron deficiency, B12/folate deficiency, chronic disease)	Polycythemia (hypoxia, polycythemia vera)
Hematocrit (Hct)	Male: 40.7–50.3% Female: 36.1–44.3%	Same as Hb	Same as Hb
Mean Corpuscular Volume (MCV)	80–100 fL	Microcytic anemias (MCV <80): Iron deficiency, thalassemia Macrocytic anemias (MCV >100): B12/Folate deficiency, alcohol abuse, liver disease	Not typically relevant
Mean Corpuscular Hemoglobin (MCH)	27–33 pg	Hypochromic anemias (iron deficiency, chronic disease)	Hyperchromic conditions (spherocytosis)
Red Cell Distribution Width (RDW)	11.5–14.5%	Normal in thalassemia	Increased in iron deficiency anemia, B12/folate deficiency

Disease-Specific RBC Analysis

Microcytic Anemias (MCV < 80 fL)

Condition	MCV	Serum Ferritin	Iron	TIBC	Peripheral Smear Findings
Iron Deficiency Anemia	↓	↓	↓	↑	Microcytosis, hypochromia
Thalassemia	↓	Normal/↑	Normal	Normal	Target cells, basophilic stippling
Anemia of Chronic Disease	↓/N	Normal/↑	↓	↓	Normocytic/microcytic RBCs

Macrocytic Anemias (MCV > 100 fL)

Condition	MCV	Reticulocyte Count	Serum B12/Folate	Peripheral Smear Findings
Vitamin B12 Deficiency	↑	↓	↓	Hypersegmented neutrophils, macro-ovalocytes
Folate Deficiency	↑	↓	↓	Same as B12 deficiency
Alcoholism/Liver Disease	↑	Normal	Normal	Macrocytosis without hypersegmentation

Normocytic Anemias (MCV 80-100 fL)

Condition	Reticulocyte Count	Other Key Tests	Peripheral Smear Findings
Acute Blood Loss	↑	Hb/Hct reduction	Normal RBCs
Hemolytic Anemia	↑	LDH ↑, Haptoglobin ↓, Bilirubin ↑	Schistocytes (DIC, TTP, HUS), Spherocytes (AIHA)
Anemia of Chronic Disease	↓	Iron ↓, Ferritin ↑, TIBC ↓	Normocytic/microcytic RBCs

2. White Blood Cell (WBC) Count and Differential

Parameter	Normal Range	Increased in	Decreased in
Total WBC Count	4,500–11,000/µL	Leukocytosis (infections, leukemia, inflammation)	Leukopenia (viral infections, bone marrow failure, sepsis)
Neutrophils (PMNs)	50–70% (2,500–7,000/µL)	Bacterial infections, stress, steroids, CML	Severe infections (sepsis), aplastic anemia
Lymphocytes	20–40% (1,000–4,000/µL)	Viral infections (EBV, CMV), chronic lymphocytic leukemia (CLL)	HIV/AIDS, corticosteroids, immunodeficiency
Monocytes	2–10%	Chronic infections (TB), autoimmune diseases, Hodgkin’s lymphoma	Aplastic anemia, bone marrow suppression
Eosinophils	1–6%	Allergies, parasitic infections, eosinophilic leukemia	Corticosteroid therapy
Basophils	<1%	Chronic myeloid leukemia (CML), hypersensitivity reactions	Stress, acute infections

WBC Disease-Specific Analysis

Leukocytosis (High WBC Count)

Condition	WBC Count	Differential Findings
Bacterial Infections	Mild ↑	↑ Neutrophils (left shift)
Viral Infections	Normal/↑	↑ Lymphocytes
Chronic Myeloid Leukemia (CML)	>50,000/µL	↑ Basophils, ↑ Myelocytes, Philadelphia chromosome (BCR-ABL)
Acute Leukemia (AML, ALL)	>20,000/µL	↑ Blasts, anemia, thrombocytopenia

Leukopenia (Low WBC Count)

Condition	WBC Count	Associated Findings
Severe Sepsis	↓	Neutropenia, DIC
HIV/AIDS	↓	CD4+ T-cell depletion
Bone Marrow Failure (Aplastic Anemia, Chemotherapy)	↓	Pancytopenia

3. Platelet Count and Clotting Disorders

Parameter	Normal Range	Decreased in	Increased in
Platelet Count	150,000–450,000/µL	Thrombocytopenia (ITP, TTP, DIC, aplastic anemia)	Thrombocytosis (Myeloproliferative disorders, inflammation)

Thrombocytopenia (Low Platelet Count)

Condition	Platelet Count	Key Features
Immune Thrombocytopenic Purpura (ITP)	<50,000	Isolated thrombocytopenia, increased megakaryocytes in bone marrow
Thrombotic Thrombocytopenic Purpura (TTP)	<20,000	Schistocytes, neurologic symptoms, fever, renal failure
Disseminated Intravascular Coagulation (DIC)	Variable	↑ D-dimer, ↓ Fibrinogen, schistocytes

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