NAVLE Hemic and lymphic

Canine Anemia (General) Study Guide

📅 March 28, 2026 ⏱ 25 min read 👁 3 views
Anemia is defined as a decreased packed cell volume (PCV), hematocrit (HCT), red blood cell (RBC) count, or hemoglobin concentration below the species-specific reference interval.

Overview and Clinical Importance

Anemia is defined as a decreased packed cell volume (PCV), hematocrit (HCT), red blood cell (RBC) count, or hemoglobin concentration below the species-specific reference interval. In dogs, anemia is one of the most frequently encountered clinical abnormalities and represents a significant category of hematologic disease on the NAVLE. Understanding the classification, pathophysiology, and diagnostic approach to anemia is essential for veterinary practitioners, as anemia itself is not a diagnosis but rather a clinical finding that reflects an underlying disease process.

Red blood cells in dogs have a normal lifespan of approximately 110-120 days. Under normal physiologic conditions, the rate of RBC production in the bone marrow equals the rate of senescent RBC removal by the mononuclear phagocyte system. Anemia develops when this balance is disrupted through one of three fundamental mechanisms: blood loss, hemolysis (RBC destruction), or decreased RBC production.

Parameter Normal Range Clinical Notes
PCV/Hematocrit 35-55% Less than 35% = anemia; Greyhounds: 52-60%
RBC Count 5.5-8.5 x 10^12/L Decreases with anemia
Hemoglobin 12-18 g/dL Hgb x 3 approximately equals PCV
MCV 60-77 fL Mean corpuscular volume; cell size
MCHC 32-36 g/dL Hemoglobin concentration
Reticulocytes Less than 60,000/uL Greater than 60,000/uL = regeneration
Total Protein 6.0-8.0 g/dL Differentiates hemorrhage from hemolysis

Normal Canine Hematologic Reference Values

Understanding normal canine hematologic parameters is fundamental to identifying and classifying anemia.

High-YieldOn NAVLE, remember that PCV below 35% indicates anemia in dogs. Greyhounds normally have higher PCVs (52-60%), while puppies may have lower normal values.

Anemia Severity Classification

Severity PCV Range Clinical Significance
Mild 30-35% Often subclinical; mild lethargy
Moderate 20-29% Pale mucous membranes, exercise intolerance
Severe 13-19% Tachycardia, tachypnea, weakness
Very Severe Less than 13% Life-threatening; emergency transfusion needed

Classification of Anemia

The most clinically useful approach is to first classify anemia based on the bone marrow regenerative response, as this immediately narrows the differential diagnosis.

Regenerative vs. Non-Regenerative Anemia

Assessment of the regenerative response is the first and most critical step in evaluating any anemic patient.

Regenerative Anemia

Definition: Bone marrow responds appropriately by increasing RBC production and releasing reticulocytes.

Diagnostic Criteria:

  • Absolute reticulocyte count greater than 60,000/uL
  • Corrected reticulocyte percentage greater than 1%
  • Polychromasia on blood smear

Causes:

  • Blood Loss: Acute or chronic hemorrhage
  • Hemolysis: Immune-mediated, infectious, oxidative, or mechanical

Non-Regenerative Anemia

Definition: Bone marrow fails to respond appropriately, indicating a production problem.

Diagnostic Criteria:

  • Absolute reticulocyte count less than 60,000/uL
  • Corrected reticulocyte percentage less than 1%
  • Absence of polychromasia

Causes:

  • Anemia of Inflammatory Disease: Most common cause
  • Chronic Kidney Disease: Decreased erythropoietin
  • Bone Marrow Disease: Aplasia, neoplasia, myelofibrosis
  • Pre-regenerative: Acute hemorrhage/hemolysis (less than 3-5 days)
High-YieldThe bone marrow takes 3-5 days to mount a regenerative response. Acute hemorrhage or hemolysis may initially appear non-regenerative ("pre-regenerative anemia"). Always consider the timeline!

Classification by RBC Indices

NAVLE TipRemember "MICROcytic HYPOchromic = IRON deficiency." Classic finding in chronic external blood loss (GI bleeding, heavy flea infestation).
Classification Definition Associated Conditions
Macrocytic MCV above reference Regenerative anemia, B12/folate deficiency
Normocytic MCV within reference Acute blood loss, anemia of inflammation, CKD
Microcytic MCV below reference Iron deficiency, portosystemic shunts
Hypochromic MCHC below reference Iron deficiency, regenerative anemia

Mechanisms and Causes of Anemia

Blood Loss Anemia

Acute Blood Loss

Causes:

  • Trauma, coagulopathies (rodenticide), ruptured splenic mass, GI ulceration

Key Features:

  • Initially normocytic, normochromic, non-regenerative
  • Becomes regenerative after 3-5 days
  • Decreased total protein (both RBCs and protein lost)

Chronic Blood Loss

Causes:

  • GI parasites (hookworms), heavy flea infestation, GI ulceration, bleeding tumors

Key Features:

  • Initially regenerative, becomes non-regenerative as iron depletes
  • Microcytic, hypochromic RBCs (iron deficiency)
  • Reactive thrombocytosis often present
High-YieldInternal hemorrhage (hemoperitoneum) does NOT cause iron deficiency because blood is recycled. Iron deficiency only occurs with EXTERNAL blood loss.

Hemolytic Anemia

Immune-Mediated Hemolytic Anemia (IMHA)

IMHA is one of the most common immune-mediated diseases in dogs and a high-yield NAVLE topic. It results from antibody-mediated RBC destruction.

Epidemiology:

  • Most common in middle-aged female dogs
  • Breed predispositions: Cocker Spaniels, English Springer Spaniels, Collies, Poodles, Irish Setters
  • 60-75% of cases are primary (idiopathic)

Secondary IMHA Triggers:

  • Infections: Babesia, Mycoplasma haemocanis, Ehrlichia
  • Drugs: Sulfonamides, cephalosporins, penicillins, NSAIDs
  • Neoplasia: Lymphoma, hemangiosarcoma

Clinical Signs:

  • Acute lethargy, weakness, exercise intolerance
  • Pale to icteric mucous membranes
  • Tachycardia, tachypnea, hepatosplenomegaly
  • Pigmenturia (hemoglobinuria or bilirubinuria)

Diagnostic Findings:

Board Tip - IMHA Diagnostic Triad: Remember "SAS": Spherocytes, Agglutination, and Significantly elevated bilirubin. The presence of 2+ indicators of immune-mediated destruction PLUS evidence of hemolysis supports definitive IMHA diagnosis.

IMHA Treatment

Prognosis:

  • Mortality rate: 26-70% (most deaths within first 2 weeks)
  • Leading causes of death: Severe anemia, pulmonary thromboembolism, DIC
  • Relapse rate: Up to 20%

Other Causes of Hemolytic Anemia

Non-Regenerative Anemia

NAVLE TipAnemia of inflammatory disease causes MILD to MODERATE anemia only. If severely anemic (PCV less than 20%) with no regeneration, think bone marrow disease, PRCA, or concurrent hemorrhage/hemolysis.
Test/Finding Expected Results
PCV Moderate to severe anemia (often less than 20%)
Blood Smear Spherocytes, polychromasia, anisocytosis, ghost cells
Saline Agglutination Positive - highly suggestive of IMHA
Coombs Test Positive - detects antibody/complement on RBCs
Bilirubin Elevated (prehepatic icterus)
Total Protein Normal to increased (protein not lost)

Diagnostic Approach

Step-by-Step Algorithm

  • Confirm Anemia: PCV less than 35%
  • Assess Regeneration: Reticulocyte count, polychromasia
  • Evaluate Total Protein: Decreased = hemorrhage; Normal = hemolysis/production
  • Examine Blood Smear: Spherocytes, Heinz bodies, parasites, schistocytes
  • Evaluate RBC Indices: MCV, MCHC
  • Additional Testing: Saline agglutination, Coombs, biochemistry, imaging
  • Bone Marrow Evaluation: For unexplained non-regenerative anemia

Differentiating Blood Loss from Hemolysis

Treatment Drug Notes
Primary Immunosuppression Prednisone 2 mg/kg/day Cornerstone of therapy; taper over 3-6 months
Secondary Immunosuppression Azathioprine, Cyclosporine, Mycophenolate For refractory cases or steroid tapering
Antithrombotic Therapy Clopidogrel, Low-dose aspirin, LMWH CRITICAL - PTE is major cause of death
Supportive Care Blood transfusion, IV fluids, O2 Transfuse when severely low PCV or hypoxic
Category Examples Key Features
Oxidative Injury Onion/garlic, Acetaminophen, Zinc Heinz bodies, eccentrocytes, methemoglobinemia
Infectious Babesia, Mycoplasma haemocanis Organisms visible on blood smear
Microangiopathic DIC, Hemangiosarcoma, Heartworm Schistocytes (RBC fragments)
Hereditary PK deficiency (Basenjis), PFK deficiency (Springers) Chronic regenerative anemia; breed-specific
Cause Mechanism Key Features
Anemia of Inflammatory Disease Hepcidin-mediated iron sequestration Most common; mild-moderate; normocytic normochromic
Chronic Kidney Disease Decreased erythropoietin Severity correlates with renal dysfunction
Bone Marrow Disease Aplasia, myelophthisis Often pancytopenia; bone marrow biopsy needed
Endocrine Disease Hypothyroidism, Hypoadrenocorticism Mild anemia; other clinical signs present
Parameter Blood Loss Hemolysis
Total Protein Decreased Normal/Increased
Bilirubin Normal Elevated
Plasma Color Clear Icteric or hemolyzed
Spherocytes Absent Present (in IMHA)

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