Blood work provides essential information about your senior pet’s internal health and organ function. It will likely be recommended as routine monitoring during their annual veterinary exam, as a pre-anesthetic and presurgical health screening, or to aid in an illness or injury diagnosis.

Unfortunately, as your pet’s age increases, so does the likelihood that their test results will be abnormal. When that time comes, ensure you’re prepared to make confident care and treatment decisions by learning the basics of senior pet blood work.

The following information is an educational guide, not intended as a substitute for veterinary diagnosis. Blood work is a complex, multifaceted diagnostic tool that only your veterinarian should interpret. But this basic guide should help pet owners understand their pet’s test results.

Your senior pet’s complete blood count (CBC)

The complete blood count (CBC) evaluates the cellular and liquid components of your pet’s blood, which is actually considered a connective tissue. Blood serves three primary purposes in the body, including transportation, regulation, and defense against foreign invaders (i.e., the immune system).

The CBC can identify infection, inflammation, and anemia by evaluating the following factors:

* Red blood cells (RBC) — RBCs are the most numerous cells and use hemoglobin to transport oxygen in the body. Red blood cell volume, shape, and size (RDW) are evaluated in a CBC. A low RBC count can indicate anemia.

* White blood cells (WBC) — WBCs include neutrophils, basophils, eosinophils, monocytes, and lymphocytes, and are primarily responsible for fighting infection. Increased WBC numbers can indicate infection or inflammation. Increased lymphocytes commonly indicate a blood cancer called lymphoma.

* Reticulocytes (RETIC) — These immature red blood cells increase during blood loss or anemia.

* Platelets (PLT) — PLT helps repair vessels and provide hemostasis (i.e., they allow blood to clot). Low platelets can be caused by excessive bleeding or immune-mediated diseases. 

* Hematocrit and total protein — This important test determines anemia and dehydration by measuring the blood's red blood cell and plasma concentrations.

Your senior pet’s general chemistry panel

The general chemistry panel blood work evaluates your pet’s organ function, electrolyte balance, and blood sugar. Typical changes in senior pet chemistry include:

* Kidney values — These values, which include blood urea nitrogen (BUN,) creatinine (CREA), phosphorous (PHOS), and total protein, will be abnormal if your pet’s kidneys fail to filter toxins from the bloodstream effectively, or to maintain fluid equilibrium (e.g., filter excess water, resulting in dehydration). Potential causes include kidney failure, cancer, infection, kidney stones, chronic medication use, or treatment protocols such as chemotherapy.

* Liver values — Elevated liver enzymes (i.e., ALP, ALT, AST, GGT) can indicate organ damage, but must be evaluated collectively because several enzymes exist elsewhere in the body. Altered liver enzymes can indicate toxin exposure, cancer, medication, bile obstruction, endocrine disease (e.g., Cushing’s disease), or infection. Additional liver values albumin (ALB) and total bilirubin (TBILI) may indicate dehydration, liver disease, or anemia.  

* Pancreatic values — Blood glucose, and digestive enzymes lipase (LIPA) and amylase (AMYL) may be elevated in a pet with pancreatic disease but can also indicate kidney or gastrointestinal conditions.

* Glucose (GLU) — Blood sugar fluctuations can be normal before or after a meal, but persistent high values (i.e., hyperglycemia) can indicate a lack of insulin production and suggest diabetes mellitus. Low blood glucose (i.e., hypoglycemia) may suggest a fasted sample, pancreatic damage, liver failure, or metabolic diseases.

* Electrolytes — Sodium (Na+), potassium (K+), and chloride (Cl-) are required for nerve impulses, muscle contraction, and other body functions, and have a narrow normal range. Kidney failure, dehydration, and excessive fluid loss through vomiting or diarrhea are common reasons for electrolyte imbalance.

* Thyroid (T4) — The thyroid gland regulates the body’s metabolic rate and blood calcium levels. A dysfunctioning thyroid gland can lead to excessive thyroid hormone production (i.e., hyperthyroidism) commonly seen in cats or deficient production (i.e., hypothyroidism), which most frequently occurs in dogs.

Next steps if your senior pet has abnormal blood work results

When making recommendations, your veterinarian will likely consider your senior pet’s overall health, previous test results, and clinical signs. If your pet’s results are only mildly altered, your veterinarian may elect to repeat the blood work at a later date. If the results are significant, further diagnostics will likely be necessary to confirm the diagnosis. Potential further testing may include:

* Additional lab work — Specific blood tests, urinalysis, or parasite screenings

* Imaging — X-rays, ultrasound, CT, or MRI scans, to visualize internal structures

* Biopsy — Needle or surgical biopsy if imaging or palpation detects an irregularity

* Surgery — Exploratory or corrective surgical intervention

A senior pet’s health may deteriorate rapidly, but routine blood work can identify many conditions before they can limit your pet’s quality of life. If your senior pet is struggling with chronic illness or debilitating disease, and you’d like end-of-life care guidance, contact our telehospice service.