Clinical pathology

Aseptic ‘clean stick’

A timely blood collection where the needle enters the vessel cleanly without undue penetration of muscle or peri-vascular tissue to avoid spurious results

EDTA (purple top) tubes

The preferred anticoagulant for haematology requires precise filling to maintain the EDTA:blood ratio and has a bacteriostatic effect

Serum vs Plasma

Plasma is the watery substance in whole blood containing clotting factors; serum is plasma without clotting factors, obtained from a clot tube after coagulation.

Reference interval 95% rule

Reference intervals encompass 95% of a healthy population, meaning 5% of healthy animals will naturally have values outside the interval (ORI)

RBC lifespan by species

Dog: 110 days, Cat: 70 days, ruminants: 140-160 days

Mean cellular haemoglobin concentration (MCHC) formula

MCHC = (Hb/PCV) x 10

Regenerative anaemia indicators

Increased reticulocytes (immature RBCs), macrocytosis (increased MCV) and Hypochromasia (decreased MCH/MCHC)

Iron deficiency anaemia classification

Microcytic, hypochromic anaemia

Microcytic (RBC smaller than normal)

Hypochromic (RBC reduced colour or hemoglobin content)

Five types of leukocytes and their increase terms

Neutrophils —> Neutrophilia

Monocytes —> Monocytosis

Lymphocytes —> Lymphocytosis

Eosinophils —> Eosinophilia

Basophils —> Basophilia

Toxic Neutrophils

Neutrophils with ‘proofreading’ errors (cytoplasmic inclusions/vacuolation) indicating rapid production and release during severe inflammatory reactions

Calculation of Absolute Leukocyte Count

WCC x % from a 100-cell differential count on a blood smear

Primary vs secondary haemostasis

Primary: Platelet plug and vessel vasoconstriction (measured by Buccal Mucosal Bleeding Time (BMBT))

Secondary: Coagulation cascade converting fibrinogen to fibrin

Activated Clotting Time (ACT)

A patient-side test for secondary haemostasis (intrinsic and common pathways) using prewarmed tubes (37C). It is prolonged once clotting factors drop below 5%

Hyperproteinaemia Vs Hypoproteinaemia

Hyperproteinaemia —> increased total plasma protein (TP)

Hypoproteinaemia —> decreased total plasma protein

Physiologic Hyperglycaemia Causes

Excitement (catecholamines suppress insulin), stress (glucocorticoids cause insulin resistance) and postprandial (after eating) states.

Spurious Hypoglycaemia

A false low glucose reading occurs because RBCs and WBCs continue to consume glucose in a blood sample that is not processed quickly.

Liver Insult Enzymes (species specific)

Dog/Cat: ALT and AST.

Horse/Cow: SDH

Azotemia types and urine specific gravity (SG)

Prerenal: Concentrated urine (1.030)

Renal: Isosthenuric (SG = 1.010, kidney compromised)

Postrenal: Oliguria (blockage/leakage, 1.015-1.030)

Fish Tank Analogy: Dehydration

Both PCV (fish concentration) and TP (gravel concentration) increase because water is removed from the tank (haemoconcentration)

Fish Tank Analogy: Recent Haemorrhage

Both PCV and TP decrease because the body restores blood volume by refilling the tank with water only, diluting the remaining fish and gravel

Fish tank analogy: Haemolysis

PCV decreases (fish eaten by 'piranha'), but TP is often unchanged or slightly increased due to inflammation.

Isosthenuria SG Range

1.008 to 1.012

Crystalluria

The presence of crystals in the urine

Cytology vs Histopathology

Cytology: Microscopic study of individual cells from fluids or aspirates

Histopathology: study of intact tissue structure/architecture from biopsies

Aggregate vs. punctate reticulocytes in cats

Aggregate reticulocytes have large clumped reticulum and reflect active bone marrow response within 24-48 hours. Punctate reticulocytes have small isolated dots and persist for 1-3 weeks

Saline dilution test (rouleaux vs agglutination)

Adding physiological saline disperses Rouleaux (linear stacking of RBCs driven by high plasma proteins), but true agglutination (antibody-mediated clumping) persists

Heinz bodies

Inclusions formed by denatured and oxidised haemoglobin attached to the inner RBC membrane, caused by oxidative toxins

Common causes of Non-regenerative Anaemia

Primary bone marrow failure (aplastic anaemia, leukaemia) or secondary extra-marrow conditions (chronic kidney disease from EPO deficit, chronic inflammatory disease, late-stage iron deficiency)

Buccal Mucosal bleeding time (BMBT)

An in vivo screening test for primary haemostasis (platelet plug formation). Prolonged BMBT indicates severe thrombocytopenia, platelet dysfunction (thrombopathia) or von Willebrand disease.

PT vs aPTT Coagulation testing

Prothrombin time (PT) tests the extrinsic and common pathways (factor VII)

Activated partial thromboplastin time (aPTT) tests the intrinsic and common pathways (factors XII, XI, IX, VIII)

Cholestatic liver enzymes (ALP and GGT)

Alkaline Phosphatase (ALP) and Gamma-Glutamyltransferase (GGT) increase in response to biliary stasis (cholestasis) or enzyme induction (e.g., corticosteroids in dogs)

Markers of decreased Hepatic functional mass

Decreased albumin, Urea (BUN), glucose, and cholesterol, along with elevated serum bile acids and resting blood ammonia

Differentiating prerenal from renal azotemia

Prerenal —> Elevated BUN/Creatinine with Hyersthenuric urine (dogs > 1.030, cats > 1.035)

Renal —> Elevated BUN/creatinine with isothenuric urine (1.008-1.012)

Hyposthenuria Definition and range

Urine specific gravity < 1.008. Indicates that renal tubules are actively reabsorbing solutes and diluting urine below plasma filtrate osmolality

transudate vs. Exudate Effusions

Transudate —> clear fluid, low protein (<25 g/L), low cell count (< 1.5 × 10^9/L)

Exudate —> Turbid fluid, high protein (>30 g/l), high cell count (>5.0 × 10^9/L)

Modified transudate features

Effusion with moderate protein concentration (25-50 g/L) and cell count (1.0-5.0 × 10^9/L) typical of congestive heart failure, neoplasia or portal hypertension.

Cytological criteria of Malignancy

Anisokaryosis (nuclear size variation), pleomorphism, increased nuclear-to-cytoplasmic ratioratio,n, multiple/variable nucleoli and abnormal mitotic figures

Suppurative vs. granulomatous inflammation cytology

Suppurative —> >85% neutrophils (acute bacterial infection or necrosis).

Granulomatous —> high proportion of macrophages and multinucleated giant cells (chronic infection, fungal or foreign body)

Urine protein-to-creatinine (UPC) ratio

A quantitative assay evaluating renal glomerular protein loss by normalising urine protein relative to urine concentration/creatinine

Renal Glucosuria

Presence of glucose in urine despite normal blood glucose levels, caused by proximal tubular transport dysfunction (e.g., Franconi syndrome, acute tubular damage)

Significance of Cellular and Granular casts in Urine

Casts are cylindrical structures formed in distal renal tubules; cellular and granular casts indicate active renal tubular damage, degeneration or necrosis.

Major Acute Phase Proteins (APPs) by Species

Dog —> C-reactive protein (CRP),

Cats and horses —> Serum Amyloid A (SAA)

Cattle —> Haptoglobin and Fibrinogen

Hyperkalaemia Causes and clinical significance

Causes —> Oliguric/anuric renal failure, urinary tract rupture/obstruction, Addison’s disease.

Significance —> Induces cardiotoxicity. Leading to bradycardia, arrhythmias and cardiac arrest

Hormonal regulation of calcium phosphate

Parathyroid Hormone (PTH) —> Increases Ca, decreases Phosphate

Calcitriol (Vit D) —> increases both Ca and phosphate.

Calcitonin —> decreases both Ca and Phosphate

Feline Pancreatitis-Specific Diagnostic Test

Feline Pancreatic Lipase Immunoreactivity (fPLi/Spec fPL)

Standard serum amylase and total lipase are unreliable in cats

Sodium Fluoride (grey top) Tube indication

Contains sodium fluoride/oxalate which inhibits glycolysis; indicated from accurate blood glucose measurement when sample separation is delayed

Lithium heparin (green top) tube indication

Contain heparin which enhances antithombin; preferred anticoagulant for rapid blood biochemistry and STAT critical care panels

Stress Leukogram Pattern

Neutrophilia (mature), lymphopenia, eosinopenia, and variable Monocytosis caused by endogenous stress or exogenous glucocorticoids.