Microscope use and Cytology

Cytology definition

Diagnostic test examining populations of cells in a sample

Cytology uses

Determine cell type in a mass; identify microorganisms; differentiate malignant vs benign tumors

Cytology vs Histopathology

Cytology: discrete cells; Histopathology: intact tissue architecture

Cytology strengths

Great for evaluating nuclei/cytoplasm; quick, cheaper, less invasive; useful for fluids/swabs; often in-house

Histopathology strengths

Evaluates tissue architecture; allows tumor grading and margin evaluation; more definitive diagnosis

Cytology sampling methods

Fine-needle aspirates, swabs, scrapes, brushes, impression smears, fluids (lavages, effusions, synovial fluid)

Blood smear monolayer

Best place to examine cells

Blood smear feathered edge

Examine first at low power; look for platelet clumps, microfilaria, large diagnostic cells

Cytology pathogens: fungi

Cryptococcosis, Blastomycosis, Aspergillosis, Sporotrichosis

Cytology pathogens: blood parasites

Babesia vogeli, Ehrlichia canis, Anaplasma phagocytophilum, Trypanosoma congolense

Cytology pathogens: bacteria

Identifiable via cytology and Gram stain

Benign neoplasia characteristics

Uniform cytoplasm, uniform nucleus size/shape, consistent N:C ratio, evenly distributed nucleoli

Cytology neoplasia examples

Mast cell tumor, melanoma, lipoma, liposarcoma, cutaneous lymphoma, injection site sarcoma

Leukocyte differential

50-100x oil immersion; count/ID 100 leukocytes in monolayer; calculate absolute WBC numbers

Platelet count thresholds

Normal >200,000/µL; <50,000 = prolonged bleeding; <30,000 = spontaneous bleeding

Platelet manual estimate

EDTA sample; smear/stain; check feathered edge; 1 platelet ≈ 15,000/µL; average 10-15 per field = normal

Canine estrus detection

Dogs: 2 cycles/year; vaginal epithelial cells change shape/staining in proestrus/estrus; cytology helps ID phase

Septic peritonitis

Inflammation of peritoneum (often secondary to GIT disruption); high morbidity; mortality 20-68%; prompt ID/treatment lifesaving

Gram stain categories

Gram (+) cocci, Gram (-) cocci, Gram (+) rods, Gram (-) rods

Gram stain limitations

Cannot ID specific species; narrows pathogens; guides antibiotic choice

Other cytology uses

Urine sediment, joint fluid analysis, lymphadenopathy, CSF analysis