How to read your cat’s blood test results

Articles · Lab Values

Your vet hands you a page of numbers, asterisks, and abbreviations, and your stress level climbs. This guide walks through the values that usually appear on a senior or chronic-care cat’s panel and, more importantly, how to read them the way clinicians do: as a story over time, not a single snapshot.

How do I actually start reading my cat’s blood test results?

Start by separating the page into two tests: the chemistry panel (organ chemistry, like kidney and liver values) and the complete blood count (CBC) (red cells, white cells, platelets). Find the column with your cat’s result and the column with the lab’s reference range next to it. Anything flagged “high” or “low” simply sits outside that range, which is a flag to discuss, not a diagnosis.

A few orientation tips before you dig in:

• Reference ranges differ by laboratory and by analyzer. A value that reads “high” at one clinic may be mid-range at another. Always compare a result to the range printed on that same report.
• One out-of-range value is rarely the whole story. A flagged result needs context; ask your veterinarian whether repeat testing or investigation is needed.
• Trends beat snapshots. A changing trend warrants review; it does not establish progression on its own.

What does a senior cat’s standard blood panel actually include?

A typical senior-cat panel bundles a chemistry panel, a CBC, a total T4 (thyroid), and often a urinalysis. The chemistry panel covers kidney markers (creatinine, BUN, SDMA, phosphorus), liver enzymes (ALT, ALP), electrolytes, calcium, glucose, and total protein. The CBC counts red cells, white cells, and platelets.

The American Animal Hospital Association and American Association of Feline Practitioners, in the 2021 AAHA/AAFP Feline Life Stage Guidelines, recommend at least annual full physical exams for all cats and exams every six months for senior cats, with lab screening guided by age and risk. That cadence is exactly why building a record of past results pays off: each panel becomes a data point in a longer line.

How do I read the kidney values (creatinine, SDMA, BUN, phosphorus)?

Read kidney markers as a group, never in isolation. Creatinine and SDMA both estimate filtration, BUN is influenced by diet and hydration as well as kidneys, and phosphorus tends to rise as kidney disease advances. When several drift the same direction over months, the pattern is more meaningful than any one number.

SDMA is the early-warning marker here. In Hall’s feline study, the fitted SDMA upper-limit estimate corresponded to about 24% lower GFR; interpretation depends on the study and reference interval. BUN and creatinine require interpretation with hydration, diet, urine findings and other results. The International Renal Interest Society (IRIS Staging of CKD, 2023) uses creatinine and SDMA together to stage chronic kidney disease, with feline creatinine stages running roughly: Stage 1 under 1.6 mg/dL, Stage 2 at 1.6 to 2.8 mg/dL, Stage 3 at 2.9 to 5.0 mg/dL, and Stage 4 above 5.0 mg/dL. For a deeper look, see our guides to what SDMA means and IRIS staging for CKD cats.

What do the liver values and thyroid number tell me?

ALT is the headline liver enzyme: it leaks into the blood when liver cells are injured, so a high ALT signals hepatocyte stress, not a specific disease. Total T4 screens the thyroid; in older cats it is checked because hyperthyroidism is common. Both are confirmation prompts, not conclusions.

A couple of practical notes:

• The Merck Veterinary Manual describes ALT as a sensitive marker of liver-cell injury in cats and dogs. Importantly, the size of the ALT increase reflects how many cells are affected, not whether the damage is permanent, and enzymes often fall again as the underlying cause is treated.
• Hyperthyroidism is an important disease in older cats; prevalence varies by country and study population. A high T4 in a senior cat is a common, treatable finding worth discussing.

What does the complete blood count (CBC) part tell me?

The CBC counts the cells floating in the blood rather than the chemistry dissolved in it. Ask your veterinary team to interpret each CBC finding, confirm sample or analyzer flags, and explain the cells involved. Red-cell measurements are useful for monitoring anemia in CKD; the rest of the CBC also needs review.

A few CBC terms you will likely see:

• HCT / PCV (hematocrit / packed cell volume) and hemoglobin: measures of red-cell mass. Low values mean anemia, which can leave a cat tired and pale. Ask your veterinary team to interpret each CBC finding, confirm sample or analyzer flags, and explain the cells involved.

Why do values get flagged when my cat seems fine?

A flagged result needs context; ask your veterinarian whether repeat testing or investigation is needed.

What helps put a flag in perspective:

• How far outside the range the value sits (a hair over versus dramatically high).
• Whether several related values agree, which strengthens the signal.
• How your cat is doing at home, since lab numbers are interpreted alongside appetite, energy, drinking, and weight.

This is exactly why your vet may say “let’s recheck that” rather than reacting to a single mild flag.

Why do trends matter more than any single number?

A changing trend warrants review; it does not establish progression on its own. Plotting each marker over time turns scattered reports into a trend line you and your vet can act on.

This is exactly where a long memory helps. Bringing old reports to an appointment lets your vet see whether a flagged value is new, stable, or worsening, which changes how urgently it needs attention.

How can I keep track of all this between vet visits?

You do not need to memorize ranges, you need a place to store and compare them. Pawtient AI’s blood-test scan and AI interpretation lets you photograph a lab report so each value is captured in plain language and plotted against your cat’s previous results, so you walk into the next visit with the trend already in front of you. Our lab value translator and FAQ can help, too.

Pawtient AI is an AI assistant and second opinion, never a diagnosis — always consult your veterinarian.

Sources

• International Renal Interest Society. IRIS Staging of CKD (modified 2023). iris-kidney.com
• Hall JA, et al. Comparison of serum concentrations of symmetric dimethylarginine and creatinine as kidney function biomarkers in cats with chronic kidney disease. Journal of Veterinary Internal Medicine, 2014.
• American Animal Hospital Association / American Association of Feline Practitioners. 2021 AAHA/AAFP Feline Life Stage Guidelines. 2021.
• Merck Veterinary Manual. Enzyme Activity in Hepatic Disease in Small Animals. merckvetmanual.com

By Pawtient AI Editorial Team. Educational content. Sources are listed below; ask your veterinarian how they apply to your pet. Not a substitute for veterinary care.