Cat Blood Tests Explained: CBC, Chemistry Panel and Thyroid Results

By Tailwisp Editorial TeamUpdated October 20, 20264 min read

Cats hide illness so well that blood tests are among the best ways to find disease early. Yet a printout of numbers can be bewildering. This guide explains the common tests, what they tell your vet and how to ask useful questions. It is general information, and your vet will interpret your cat's own results.

Why vets run blood tests

• To investigate signs, such as vomiting, weight loss or increased thirst.
• To screen healthy cats, especially seniors.
• Before anesthesia, such as dental cleaning. See cat dental cleaning: what to expect.
• To monitor chronic disease or medication.
• To set a baseline for future comparison.

Complete blood count (CBC)

A CBC counts the cells in blood.

• Red blood cells, hematocrit and hemoglobin. Low values suggest anemia, from blood loss, disease or bone marrow problems. High values may reflect dehydration.
• White blood cells. Raised counts may suggest infection or inflammation, and low counts may suggest viral disease or bone marrow suppression. The mix of types gives more clues.
• Platelets. These help blood clot.
• Reticulocytes. Young red cells, showing whether the marrow is responding to anemia.

Chemistry panel

A chemistry panel measures substances in blood that reflect organs:

• BUN and creatinine, kidney markers that rise in kidney disease, but also with dehydration. See chronic kidney disease in cats.
• SDMA. A kidney marker that can rise earlier than creatinine, and is less affected by muscle mass.
• ALT, ALP and bilirubin, liver markers. See hepatic lipidosis in cats.
• Glucose. High in diabetes, but can rise with stress. See diabetes in cats.
• Total protein, albumin and globulin.
• Electrolytes, such as sodium, potassium and calcium.
• Cholesterol, amylase and lipase, which may be altered in pancreatic disease. See pancreatitis in cats.
• Phosphorus. Raised in kidney disease.

Thyroid test (total T4)

Total T4 measures thyroid hormone, and a high level suggests hyperthyroidism, common in older cats. See hyperthyroidism in cats. Some cats with early disease or other illness need further thyroid tests.

Other tests

• Urinalysis, to assess kidney function, infection and crystals, usually alongside blood work.
• FeLV and FIV tests. See FeLV and FIV in cats.
• Fructosamine, to assess long-term blood sugar.
• Feline pancreatic lipase, to help diagnose pancreatitis.
• Cobalamin and folate, for gut disease.
• Blood pressure, not a blood test, but often paired with them. See high blood pressure in cats.

Reading results

Labs print a reference range, which is the span in which most healthy cats fall. Results outside the range are flagged, but they need context: a slightly high value in a stressed or dehydrated cat may not be meaningful, and a value inside the range may still be abnormal for your cat if it has changed over time. That is why a baseline is useful, and why vets compare trends. Ask your vet what is abnormal, how serious it is, whether to repeat the test and what next steps they recommend.

Preparing your cat

Your vet may ask you to fast your cat for several hours, which gives clearer results, especially for fats and glucose. Follow instructions about water. Keep your cat calm, since stress can raise glucose and white cell counts. See helping a cat who hates the vet.

Cost and frequency

Costs vary, and panels come in different sizes. Ask your vet which tests matter most. Many recommend a baseline for adult cats, annual tests from about seven years, and twice-yearly checks for geriatric cats. See cat vet visit costs and senior cat care guide.

In-house tests and outside labs

Many clinics run common tests on machines in the building, with results in minutes, which is useful in emergencies. Others send samples to an outside lab, which may offer more detailed tests, and a specialist review of cell appearance. Ask which approach is being used, and when to expect results. If a test is unexpected, such as a very high white cell count, the vet may ask a pathologist to examine a blood smear.

Why trends matter more than single numbers

Your cat has its own normal. A creatinine value that is within range, but has climbed by half over two years, may signal early kidney disease. That is why vets keep results, and why a baseline taken when your cat is young and healthy is valuable. Ask for a copy of each result, and keep them in a folder or on your phone.

Hydration and stress effects

Dehydration concentrates blood, and can raise some values. Stress raises glucose in cats, sometimes dramatically, which can mimic diabetes. If this happens, vets may use fructosamine, which reflects blood sugar over weeks, to tell stress from true disease. Telling your vet about vomiting, diarrhea or poor drinking helps them interpret results.

Using results at home

If your cat has a condition such as kidney disease, results guide diet, medication and fluid therapy. Ask your vet which values to watch, what the target is and when to recheck. Keep a note of weight, appetite and thirst alongside the results.

When to see a vet

See a vet if your cat has vomiting, weight loss, thirst or lethargy. Use the US vet directory to find a clinic.

This article is general educational information, not veterinary advice. Every cat is different. If your cat is unwell, or you are unsure about a symptom, diet change or medication, contact your veterinarian.