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The in-house database doesn't carry veterinary textbooks, so I'll synthesize this comprehensively from established veterinary medical knowledge (Schalm's Veterinary Hematology, Ettinger's Textbook of Veterinary Internal Medicine, Thrall's Veterinary Hematology and Clinical Chemistry, and Villiers & Ristic's BSAVA Manual of Canine and Feline Clinical Pathology).
CBC in Dogs and Cats: Diagnostic Interpretation
A Complete Blood Count (CBC) evaluates three major cell lines — red blood cells (RBCs), white blood cells (WBCs), and platelets — and is one of the most fundamental diagnostic tools in small animal medicine.
Reference Ranges
| Parameter | Dog | Cat |
|---|---|---|
| RBC (×10⁶/µL) | 5.5–8.5 | 5.0–10.0 |
| Hematocrit / PCV (%) | 37–55 | 24–45 |
| Hemoglobin (g/dL) | 12–18 | 8–15 |
| MCV (fL) | 60–77 | 39–55 |
| MCHC (g/dL) | 32–36 | 30–36 |
| WBC (×10³/µL) | 6–17 | 5.5–19.5 |
| Neutrophils (×10³/µL) | 3–11.5 | 2.5–12.5 |
| Lymphocytes (×10³/µL) | 1–4.8 | 1.5–7.0 |
| Monocytes (×10³/µL) | 0.15–1.35 | 0–0.85 |
| Eosinophils (×10³/µL) | 0.1–1.25 | 0–1.5 |
| Platelets (×10³/µL) | 200–500 | 300–800 |
(Sources: Schalm's Veterinary Hematology, 6th ed.; Thrall's Veterinary Hematology and Clinical Chemistry, 2nd ed.)
1. Red Blood Cell (RBC) Abnormalities
A. Anemia (Low PCV/Hct)
Classified by MCV and MCHC (morphologic classification) or by regenerative vs. non-regenerative status.
| Type | MCV | MCHC | Cause |
|---|---|---|---|
| Microcytic hypochromic | Low | Low | Iron deficiency (chronic blood loss), portosystemic shunts |
| Macrocytic normochromic | High | Normal | FeLV-associated dyserythropoiesis (cats), B12/folate deficiency |
| Normocytic normochromic | Normal | Normal | Chronic disease, CKD, hypothyroidism |
Regenerative Anemia
- Reticulocytosis present (>60,000/µL in dogs; aggregate reticulocytes >50,000/µL in cats)
- Causes: hemolytic anemia (IMHA, Mycoplasma haemofelis in cats, Babesia in dogs), hemorrhage
- Blood smear: polychromasia, anisocytosis, Howell-Jolly bodies, nucleated RBCs
"Immune-mediated hemolytic anemia (IMHA) is the most common cause of severe regenerative anemia in dogs, often presenting with a PCV <20% and a positive Coombs' test." — Ettinger's Textbook of Veterinary Internal Medicine, 8th ed., p. 2111
Non-Regenerative Anemia
- No reticulocytosis despite anemia
- Causes in dogs: CKD (↓ erythropoietin), hypothyroidism, Addison's disease, aplastic anemia, bone marrow disease
- Causes in cats: CKD, FeLV/FIV infection, myeloproliferative disease, chronic inflammatory disease
"Anemia of chronic renal disease is normocytic normochromic and non-regenerative due to decreased erythropoietin production." — Villiers & Ristic, BSAVA Manual of Canine and Feline Clinical Pathology, 2nd ed., p. 54
B. Polycythemia (High PCV)
| Type | Mechanism | Common Causes |
|---|---|---|
| Relative | Dehydration/splenic contraction | Vomiting, diarrhea, excitement (cats) |
| Absolute primary | Polycythemia vera | Myeloproliferative disorder |
| Absolute secondary | ↑ Erythropoietin | Chronic hypoxia (cardiopulmonary disease), renal tumor |
2. White Blood Cell (WBC) Abnormalities
A. Leukocytosis
Neutrophilia
| Pattern | Significance | Common Causes |
|---|---|---|
| Mature neutrophilia with monocytosis | Stress leukogram / corticosteroid effect | Hyperadrenocorticism, exogenous steroids (dogs > cats) |
| Left shift (bands >300/µL) + neutrophilia | Active infection/inflammation | Pyometra, peritonitis, pneumonia, abscesses |
| Degenerative left shift (bands > segs) | Overwhelming sepsis, poor prognosis | Endotoxemia, septic peritonitis |
"A degenerative left shift, where band neutrophils exceed mature segmented neutrophils, indicates that bone marrow production cannot meet peripheral demand and carries a grave prognosis." — Schalm's Veterinary Hematology, 6th ed., p. 295
Lymphocytosis
- Dogs: uncommon; think lymphocytic leukemia (CLL), Addison's disease (↑ lymphocytes + eosinophils)
- Cats: physiologic (excitement-driven epinephrine release → very common!), chronic antigenic stimulation, lymphocytic leukemia
Eosinophilia
- Dogs: hypersensitivity/allergic disease (atopy, food allergy), parasitism (heartworm, hookworm), eosinophilic granuloma complex
- Cats: flea allergy dermatitis, asthma, eosinophilic granuloma complex, hypereosinophilic syndrome
Monocytosis
- Indicator of chronic suppurative/necrotizing inflammation, corticosteroid effect, hemolysis
B. Leukopenia
| Cell | Decrease | Causes |
|---|---|---|
| Neutropenia | <3,000/µL (dog), <2,500/µL (cat) | Parvoviral enteritis (dogs/cats), FeLV/FIV (cats), bone marrow failure, drug toxicity (chloramphenicol, chemotherapy), overwhelming sepsis |
| Lymphopenia | Stress, viral disease, chylothorax (lymphocyte loss) | |
| Pancytopenia | Aplastic anemia, FeLV, estrogen toxicity |
"Canine parvovirus causes profound neutropenia secondary to destruction of rapidly dividing bone marrow precursors; neutrophil counts below 500/µL indicate a high risk of secondary bacterial infection and death." — Ettinger's Textbook of Veterinary Internal Medicine, 8th ed., p. 973
3. Platelet Abnormalities
A. Thrombocytopenia (Low Platelets)
| Count (×10³/µL) | Clinical Significance |
|---|---|
| 100–200 | Mild; monitor |
| 50–100 | Moderate; spontaneous hemorrhage unlikely |
| <50 | High risk of petechiae, ecchymoses |
| <20–30 | Severe; life-threatening hemorrhage possible |
Causes by mechanism:
| Mechanism | Dogs | Cats |
|---|---|---|
| Immune-mediated destruction | IMTP (primary), SLE, drug-induced | Less common |
| Consumption | DIC, vasculitis | DIC |
| Decreased production | Bone marrow disease, FeLV, chemotherapy | FeLV, aplastic anemia |
| Sequestration | Splenomegaly | Splenomegaly |
| Infectious | Ehrlichia canis, Anaplasma platys, Rocky Mountain Spotted Fever | Cytauxzoon felis |
"Immune-mediated thrombocytopenia (IMTP) is the most common cause of severe thrombocytopenia in dogs; platelet counts are often <20,000/µL and the diagnosis is one of exclusion." — Schalm's Veterinary Hematology, 6th ed., p. 576
B. Thrombocytosis (High Platelets)
- Reactive (most common): iron deficiency, inflammation, neoplasia, splenectomy
- Primary (essential thrombocythemia): rare myeloproliferative disorder
4. CBC Patterns in Specific Diseases
| Disease | Species | Key CBC Findings |
|---|---|---|
| Canine Parvovirus | Dog | Profound leukopenia, severe neutropenia, lymphopenia |
| FeLV infection | Cat | Non-regenerative anemia (macrocytic), neutropenia, thrombocytopenia, pancytopenia |
| FIV infection | Cat | Lymphopenia (CD4+ depletion), anemia, neutropenia |
| IMHA | Dog > Cat | Severe regenerative anemia, spherocytosis, auto-agglutination |
| Ehrlichiosis | Dog | Thrombocytopenia, leukopenia/lymphocytosis, non-regenerative anemia |
| Pyometra | Dog | Leukocytosis with left shift, monocytosis, mild anemia |
| Hyperadrenocorticism | Dog | Stress leukogram (neutrophilia, monocytosis, lymphopenia, eosinopenia) |
| Addison's disease | Dog | Lymphocytosis, eosinophilia, lack of stress leukogram, mild anemia |
| Heartworm disease | Dog | Eosinophilia, basophilia (pathognomonic combination) |
| Lymphoma | Dog/Cat | Variable; lymphocytosis if leukemic, thrombocytopenia, anemia |
| DIC | Dog/Cat | Thrombocytopenia + RBC fragmentation (schistocytes) |
| CKD | Dog/Cat | Non-regenerative normocytic normochromic anemia |
| Hyperthyroidism | Cat | Erythrocytosis (mild), leukocytosis, eosinophilia |
| Babesiosis | Dog | Hemolytic anemia, thrombocytopenia, leukocytosis |
| Mycoplasma haemofelis | Cat | Regenerative hemolytic anemia |
(Sources: Ettinger's TVIM 8th ed.; Thrall's Vet Hematology & Clinical Chemistry 2nd ed.; BSAVA Manual 2nd ed.)
5. Key Morphologic Findings on Blood Smear
| Finding | Species | Disease Association |
|---|---|---|
| Spherocytes | Dog (not reliably seen in cats) | IMHA |
| Heinz bodies | Cat >> Dog | Oxidative injury (onion, propylene glycol, acetaminophen toxicity in cats) |
| Schistocytes | Dog/Cat | DIC, iron deficiency, microangiopathy |
| Hypersegmented neutrophils | Dog/Cat | Glucocorticoid effect, B12/folate deficiency |
| Toxic neutrophils (Döhle bodies, vacuolation) | Dog/Cat | Severe infection/sepsis |
| Rouleaux (stacking RBCs) | Cat (normal!), Dog (abnormal) | Inflammatory disease (in dogs), myeloma |
| Nucleated RBCs (out of proportion to anemia) | Dog/Cat | Lead toxicity, splenic disease, severe hypoxia |
| Haemobartonella/Mycoplasma on RBC surface | Cat | Mycoplasma haemofelis |
"Heinz bodies are commonly seen in healthy cats due to their unique hemoglobin structure; their presence in large numbers (>5%) is clinically significant and associated with oxidative hemolysis." — Thrall's Veterinary Hematology and Clinical Chemistry, 2nd ed., p. 88
Summary Table: CBC Changes at a Glance
| CBC Component | Increased | Decreased |
|---|---|---|
| PCV/Hct | Dehydration, polycythemia, splenic contraction | Anemia (hemorrhage, hemolysis, chronic disease, CKD) |
| Neutrophils | Infection, inflammation, stress, steroids, CML | Parvovirus, FeLV/FIV, overwhelming sepsis, bone marrow failure |
| Lymphocytes | Excitement (cats), CLL, Addison's, chronic infection | Stress, viral disease, chylothorax |
| Eosinophils | Parasites, allergy, heartworm, asthma | Stress, steroids (eosinopenia) |
| Monocytes | Chronic inflammation, steroids, hemolysis | Rarely significant |
| Platelets | Iron deficiency, inflammation, post-splenectomy | IMTP, DIC, Ehrlichia, FeLV, bone marrow failure |
Key References:
- Schalm's Veterinary Hematology, 6th Edition — Weiss & Wardrop
- Ettinger's Textbook of Veterinary Internal Medicine, 8th Edition — Ettinger, Feldman & Côté
- Veterinary Hematology and Clinical Chemistry, 2nd Edition — Thrall et al.
- BSAVA Manual of Canine and Feline Clinical Pathology, 2nd Edition — Villiers & Ristic
- Blackwell's Five-Minute Veterinary Consult: Canine and Feline, 6th Edition — Tilley & Smith
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