What your cat's blood work actually means

Why vets run blood work on cats

Cats are masters at hiding illness. By the time a cat shows obvious symptoms — eating less, hiding more, losing weight — something may have been developing for weeks or months. Blood tests catch problems that a physical exam alone can miss.

Your vet will typically run blood work during annual wellness visits (especially for cats over seven), before surgery or anesthesia, when your cat seems unwell, or to monitor a known condition like kidney disease or diabetes.

The two main panels are a complete blood count (CBC) and a chemistry panel. Many vets also check a thyroid level, especially in older cats. Here's what each part measures in plain language.

The complete blood count (CBC)

A CBC looks at the cells in your cat's blood — red cells, white cells, and platelets. It helps your vet spot anemia, infections, inflammation, and clotting problems.

Red blood cells (RBC) and hematocrit (HCT)

Red blood cells carry oxygen. Hematocrit is the percentage of blood volume made up of red blood cells.

Low hematocrit in cats can indicate anemia — and feline anemia has causes that differ from dogs. Chronic kidney disease is one of the most common causes of anemia in older cats, because the kidneys produce a hormone (erythropoietin) that tells the bone marrow to make red blood cells. Infections like FeLV (feline leukemia virus) can also suppress red blood cell production.

High hematocrit sometimes appears with dehydration — common in cats who don't drink enough water.

A good question for your vet: "Is the low hematocrit likely related to kidney function, or should we check for other causes?"

White blood cells (WBC)

White blood cells fight infection and respond to inflammation. The CBC breaks them into subtypes:

• Neutrophils — the first responders. High counts often point to bacterial infection, stress, or inflammation. Very low counts can indicate overwhelming infection or bone marrow problems.
• Lymphocytes — key players in the immune system. Elevated lymphocytes in cats can be associated with chronic inflammation or, in some cases, lymphoma — the most common cancer in cats. A single high reading isn't a diagnosis, but your vet may want to monitor it.
• Eosinophils — often elevated with allergies, parasites, or feline asthma (a condition more common in cats than many owners realize).
• Monocytes — can increase with chronic inflammation or recovery from infection.

A good question for your vet: "Are the white cell subtypes pointing toward a specific kind of problem?"

Platelets (PLT)

Platelets help blood clot. Low platelets can mean increased bleeding risk. In cats, one quirk to know: cat platelets tend to clump in the collection tube, which can cause a falsely low automated count. If the machine reads low platelets but your cat has no bruising or bleeding, your vet will often check a blood smear manually before worrying.

The chemistry panel

The chemistry panel measures substances in the blood that reflect organ function — especially the kidneys, liver, and pancreas. Cats have some species-specific patterns that differ from dogs.

Kidney values: BUN, creatinine, and SDMA

Kidney disease is the most common chronic illness in older cats. BUN (blood urea nitrogen) and creatinine are waste products filtered by the kidneys. When both are elevated, it usually means the kidneys are losing filtering capacity.

Here's the tricky part: by the time creatinine is clearly elevated, a cat may have already lost 65–75% of kidney function. That's why many labs now include SDMA, a newer marker that can flag kidney changes earlier — sometimes months before creatinine rises.

If your vet mentions early kidney disease based on SDMA, take it seriously even if creatinine looks normal. Early management (diet changes, hydration support) can meaningfully slow progression.

A good question for your vet: "What stage of kidney disease are we looking at, and what can we do at home to slow it down?"

Liver values: ALT, ALP, and bilirubin

ALT (alanine aminotransferase) rises when liver cells are damaged. ALP (alkaline phosphatase) in cats is more significant than in dogs — cats have a much shorter half-life for this enzyme, so even moderately elevated ALP in a cat warrants attention.

Bilirubin comes from red blood cell breakdown, processed by the liver. Elevated bilirubin can cause jaundice (yellowing of the gums, ears, and whites of the eyes) and points to liver disease, bile duct obstruction, or accelerated red blood cell destruction.

Hepatic lipidosis — fatty liver disease — is a cat-specific emergency that can develop when a cat stops eating for even a few days, especially in overweight cats. Liver values are one of the first clues.

A good question for your vet: "Are these liver values high enough to need imaging or more specific tests?"

Blood sugar: glucose

Diabetes mellitus is common in cats, especially overweight middle-aged and older cats. But here's the catch: stress hyperglycemia is extremely common in cats at the vet. A scared, struggling cat can have glucose readings of 300+ mg/dL that would look diabetic, but are actually just a stress response.

Your vet may check fructosamine — a value that reflects average blood sugar over the past 2–3 weeks — to tell the difference between true diabetes and stress-induced spikes. This is one of the most important cat-specific nuances in blood work interpretation.

A good question for your vet: "Is this glucose reading likely stress, or should we check fructosamine?"

Pancreas values: fPLI

Pancreatitis in cats is sneaky. It often doesn't cause the dramatic vomiting and pain seen in dogs. A cat with pancreatitis might just be a little quieter, eating less, or losing weight gradually. The specific test is fPLI (feline pancreatic lipase immunoreactivity) — the general lipase and amylase tests used in dogs are less reliable in cats.

Chronic low-grade pancreatitis can coexist with inflammatory bowel disease and cholangitis (liver inflammation) in a pattern sometimes called "triaditis." If your vet mentions this, it means they're seeing signs of inflammation in multiple connected organs.

Electrolytes: sodium, potassium, chloride, phosphorus

Electrolyte imbalances in cats often tie back to kidney disease, urinary obstruction (especially in male cats — a true emergency), vomiting, or dehydration. Phosphorus is particularly important in cats with kidney disease — high phosphorus accelerates kidney damage, and managing it is a key part of treatment.

Low potassium can cause muscle weakness and a characteristic "head drop" where the cat can't hold their head up properly. It's treatable once identified.

Protein: total protein and albumin

Low albumin in cats can indicate protein loss through the gut (inflammatory bowel disease) or kidneys, or reduced production from liver disease. High total protein can appear with chronic inflammation, dehydration, or certain infections like FIP (feline infectious peritonitis).

Thyroid panel

While dogs develop hypothyroidism (too little thyroid hormone), cats get the opposite: hyperthyroidism — too much thyroid hormone. It's one of the most common endocrine diseases in older cats.

The main test is T4 (total thyroxine). A high T4 with symptoms like weight loss despite good appetite, increased thirst, restlessness, or a racing heart strongly suggests hyperthyroidism. Treatment options include medication (methimazole), radioactive iodine therapy, or a prescription diet.

One wrinkle: hyperthyroidism increases blood flow to the kidneys, which can mask underlying kidney disease. When the thyroid is treated and blood flow normalizes, kidney values may rise. Your vet should check kidney function alongside thyroid treatment to catch this early.

A good question for your vet: "If we treat the thyroid, could that unmask kidney problems? How will we monitor for that?"

What "flagged" values actually mean

Lab reports mark values outside the reference range with flags — H for high, L for low. This is the part that sends cat owners to Google at midnight.

A few things to keep in mind:

• One slightly off value in an otherwise normal panel is often noise. Reference ranges capture 95% of healthy animals — by definition, 5% of normal cats will have a value outside the range.
• Trends matter more than snapshots. A creatinine of 2.5 in a cat whose creatinine was 1.2 last year is very different from a cat who's always been at 2.3. This is why keeping historical records is so valuable.
• Cat-specific reference ranges exist for a reason. Feline normal ranges differ from canine — don't compare your cat's results to a dog's chart you found online.
• Stress affects almost everything. A terrified cat at the vet can have elevated glucose, white blood cells, and even some liver enzymes just from the stress response. If your cat is a known "vet hater," mention that — it helps your vet calibrate the results.

How to get more from your vet visit

Blood work conversations are often rushed. Here's how to make the most of yours:

• Bring previous results. Trends across tests are far more informative than a single snapshot. If you've used different vets, consolidate the records.
• Ask about the pattern. "What does the overall picture look like?" is better than fixating on one number.
• Ask what to watch for at home. If values need monitoring, your vet can tell you what behavioral or appetite changes would warrant an earlier recheck.
• Request a copy. You're entitled to your cat's lab results. Keep them — they're useful at emergency visits, specialist appointments, or when you switch vets.
• Mention stress levels. If your cat was especially distressed during blood draw, tell your vet. It genuinely affects result interpretation.

Keeping track of it all

Cats live 15–20 years. Over that lifetime, they'll accumulate dozens of lab reports from annual checkups, illness workups, and chronic disease monitoring. The cats with the best ongoing care tend to have owners who keep everything in one place — so any vet, at any visit, can see the full picture.

Voocie was built for exactly this. Upload your vet PDFs, and Voocie extracts the lab values, organizes them on a timeline, and uses AI to explain what the numbers mean in plain language. When you visit a new vet or an ER, share your cat's complete record instantly — no phone tag, no faxing.

By Voocie Team · August 5, 2026