Understanding Your Pet's Blood Work

When your vet hands you a lab report, it can look like a foreign language. Understanding the basics helps you participate in your pet's healthcare decisions.

The Complete Blood Count (CBC)

The CBC evaluates red blood cells, white blood cells, and platelets.

Red Blood Cells (RBC): Carry oxygen. Low = anemia (bleeding, kidney disease, immune disease). High = dehydration.

Hematocrit (HCT/PCV): Percentage of blood that is red cells. Normal 35-55% in dogs, 30-45% in cats.

White Blood Cells (WBC): Fight infection. High = infection, inflammation, stress. Low = bone marrow suppression, <a href="/conditions/canine-parvovirus">parvo</a>, <a href="/conditions/feline-panleukopenia">panleukopenia</a>.

Platelets: Form clots. Low = bleeding risk (immune disease, cancer, tick disease).

The Chemistry Panel

Evaluates organ function and metabolic state.

BUN and Creatinine — Kidney Function: Elevated BUN + elevated creatinine = kidney problem. Elevated BUN with normal creatinine may be dehydration. SDMA detects kidney disease earlier than creatinine.

ALT and AST — Liver Cell Health: Elevated = liver cell damage (hepatitis, toxins, certain drugs). Mild elevations can be from dental disease.

ALP and GGT — Bile Flow: Elevated with bile duct issues, pancreatitis, or steroid use. ALP also increases in growing puppies.

Total Bilirubin — Jaundice Marker: High = jaundice (liver disease, bile duct blockage, hemolytic anemia).

Glucose — Blood Sugar: Low = insulinoma, sepsis, liver failure. High = diabetes, stress.

Total Protein and Albumin: Low albumin with high globulin suggests <a href="/conditions/feline-infectious-peritonitis">FIP</a> in cats.

Electrolytes (Na, K, Cl): Abnormalities in vomiting, diarrhea, Addison's disease, kidney disease. High potassium with low sodium is classic for Addison's.

The Urinalysis

Urine specific gravity (USG) shows how concentrated the urine is. Dilute urine + elevated kidney values = kidney disease.

Protein in urine: May indicate kidney damage. Further quantification with UPC ratio.

Crystals: Struvite or calcium oxalate crystals may predispose to stones.

Bacteria: Indicates UTI, but contamination possible.

Thyroid Testing

T4 (total thyroxine): Low in hypothyroid dogs. High in hyperthyroid cats.

Free T4 by equilibrium dialysis: More accurate when total T4 is borderline.

When Numbers Are "Off" but Your Pet Seems Fine

Mildly abnormal values in an otherwise healthy pet often normalize on recheck. Liver enzymes can elevate from dental disease. Kidney values can be temporarily elevated from dehydration. Your vet will interpret results in the context of your pet's history and physical exam.