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. Mild flags can come from a stressful car ride, a recent meal, or mild dehydration.
• Trends beat snapshots. A creatinine of 2.0 means something very different if last year it was 1.1 versus if it was already 2.0.

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. According to Hall and colleagues in the Journal of Veterinary Internal Medicine (2014), SDMA can rise when roughly 25% of kidney function is lost, whereas creatinine and BUN often stay normal until about 75% is gone. That is why SDMA frequently increases months before creatinine. 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 one of the most common endocrine diseases in older cats, with an estimated prevalence over 10% in cats older than 10 years across multiple population studies. 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. It reports red blood cells (which carry oxygen), white blood cells (the immune system), and platelets (which help clotting). For a chronic-care cat, the red-cell numbers matter most, because anemia is a common companion to long-standing kidney disease.

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.
• WBC (white blood cell count): can rise with infection, inflammation, or stress, and fall in some conditions. Stress alone can shift a cat’s white-cell pattern.
• Platelets: very low counts can affect clotting, though cat samples sometimes clump platelets and under-report them, which your vet accounts for.

Because these can move with stress and sampling, the CBC is read together with the chemistry panel and how your cat looks and acts.

Why do values get flagged when my cat seems fine?

A flag simply means a value sits outside the lab’s reference range, which is built from a population of healthy animals; a few mild flags in a well cat are common and often not alarming. Stress, a recent meal, mild dehydration, or normal individual variation can all nudge a value past the cutoff without signaling disease. Context and rechecks sort the meaningful flags from the harmless ones.

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?

Because a cat’s body buffers a lot before a value moves, the direction and speed of change carry the real signal. A creatinine creeping from 1.4 to 1.7 to 2.0 over three checks tells a clearer story than one isolated 2.0. 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 reviewed against published veterinary guidelines (IRIS, AAHA, WSAVA, ACVIM, AAFP). Not a substitute for veterinary care.