Your cat had blood drawn, maybe at the senior wellness visit, maybe before a dental, maybe because she'd been drinking more water than usual and you mentioned it. A few days later the clinic emails the results, or hands you the printout at checkout, and it's thirty acronyms, a column of numbers, a stack of reference ranges, and a couple of little arrows pointing up or down. The front desk said the DVM would call if anything looked concerning. Nobody's called. You still can't read the page.
This is the page the clinic rarely has time to walk through, and the one that, walked through once, makes every future panel easier to read. A cat's bloodwork asks the same two big questions a dog's does, plus two that matter more in cats. The CBC, the complete blood count, asks how the blood itself is doing: enough red cells, white cells in a normal pattern, platelets in range. The chemistry panel asks how the organs the blood serves are doing: liver, kidneys, electrolytes, blood sugar, protein. The two that earn extra attention in cats are the kidney cluster and the thyroid number, because chronic kidney disease and hyperthyroidism are two of the most common things a senior cat panel is actually looking for.
The CBC: red cells, white cells, platelets
The CBC is the cell-count test. The Merck Veterinary Manual, the reference textbook clinicians use, treats it as the first filter for anemia, infection, inflammation, and clotting trouble, and every chemistry abnormality gets read against it.
On the red side, HCT (hematocrit) and HGB (hemoglobin) are the headline numbers, and both drop when a cat is anemic. Cats hide anemia well. A cat will compensate for a slowly falling red cell count until the drop is steep, which is part of why the number on the page sometimes surprises owners whose cat seemed fine at home. The lab also reads reticulocytes, the young red cells, to tell whether the marrow is responding to the loss (regenerative) or not (non-regenerative), and those two point at very different causes.
On the white side, WBC is the total count, but the differential, the breakdown of neutrophils, lymphocytes, monocytes, eosinophils, and basophils, is what tells the story. Cats run a strong stress response on bloodwork. A stress leukogram, high neutrophils with low lymphocytes, shows up in cats from the car ride and the exam room alone, and a good DVM reads a white-cell shift against how stressed the cat was, not just against the reference range.
Platelets matter for clotting, and in cats the analyzer count is famously unreliable because feline platelets clump during the draw. A low platelet flag on a cat very often resolves to clumping on a manual smear review, which is why the lab usually adds that note and looks at the slide before anyone treats the count as real.
Liver values: ALT, ALP, AST, GGT, bilirubin
The liver values are where a lot of owner worry lands. ALT, alanine aminotransferase, is an enzyme released when liver cells are damaged, and it's the most liver-specific number on the panel. ALP, alkaline phosphatase, is the second one to know, and here cats differ from dogs in a way worth understanding. Feline ALP has a much shorter half-life than canine ALP, so any meaningful ALP elevation in a cat tends to carry more weight than the same flag would in a dog. The Merck Vet Manual is direct about this: a raised ALP in a cat is a number the DVM takes seriously rather than waves off.
The scenario behind feline liver enzymes that techs learn to watch for is the cat who stopped eating. A cat who goes off food for even a few days can develop hepatic lipidosis, fatty liver, which drives liver enzymes up and is genuinely dangerous if it isn't caught. If your cat's liver numbers are flagged and she's also been skipping meals, that combination is the one that moves a recheck up the calendar. The walk-through of what it means when a cat stops eating covers the appetite side of this.
AST, aspartate aminotransferase, and GGT, gamma-glutamyl transferase, are the supporting cast, read alongside ALT and ALP rather than instead of them. Total bilirubin, with or without visible yellowing of the ears or gums, shifts the conversation toward bile flow or red cell destruction, and usually a same-week recheck or abdominal imaging follows.
Kidney values: BUN, creatinine, SDMA, urine specific gravity, phosphorus
The kidney panel is the part of a senior cat's bloodwork that deserves the most attention, because chronic kidney disease is one of the most common conditions in older cats, and bloodwork is how it gets caught. BUN, blood urea nitrogen, tracks how the kidneys are clearing waste, but it's also pushed around by diet and dehydration, so it's a noisier number than creatinine. Creatinine is the one most DVMs watch over time. SDMA, symmetric dimethylarginine, is a newer kidney marker IDEXX brought to market in 2015, and it rises earlier in kidney decline than creatinine does. The International Renal Interest Society, the group whose staging scale most vets use, folded SDMA into its chronic kidney disease staging for that reason. The IRIS scale runs from stage 1, the earliest, to stage 4, the most advanced.
None of those blood numbers means much without the urine. Urine specific gravity, USG, is the simple test that tells the DVM whether the kidneys are still concentrating properly. In cats this matters even more than in dogs, because a cat with rising creatinine and SDMA but dilute urine that won't concentrate is showing the kidneys losing one of their core jobs. Phosphorus rides alongside the kidney cluster too. As kidney function falls, phosphorus tends to climb, and the IRIS guidelines use phosphorus targets to guide diet and treatment at each stage. The general guide to kidney disease in dogs and cats goes deeper on what staging means day to day.
The thyroid number: total T4
The thyroid number is the line that has no real equivalent on a dog's panel. Total T4, thyroxine, is the main thyroid hormone, and in cats the concern is almost always too much of it. Hyperthyroidism, an overactive thyroid, is common in older cats and is one of the conditions a senior cat panel is specifically screening for. The classic picture is a cat over ten who's losing weight while eating well, sometimes with a faster heart rate or a new yowl at night, and a high T4 is what confirms it.
One wrinkle is worth knowing. A sick cat with another illness can have a T4 that reads falsely normal, which is why a DVM who strongly suspects hyperthyroidism may run a free T4 or repeat the test rather than rule it out on a single in-range number. If your cat's T4 is flagged high, the next conversation is about treatment options, and Plumb's, the veterinary drug handbook most US vets keep on the desk, has the dosing ranges for the medication used most often. The dose your vet sets is the one that matters for your cat. Plumb's gives the range; the clinic gives the number.
Electrolytes, glucose, protein
Sodium, potassium, and chloride read hydration and acid-base balance. In a cat, potassium is the one to keep an eye on, because cats with kidney disease can run low on it, and low potassium can cause the weakness and neck-drop that sometimes brings a cat in.
Glucose is where cats earn their reputation. Stress alone can push a cat's blood sugar up, sometimes well into a range that would mean diabetes in a calm patient. The first time I watched my own cat Bishop spike a glucose at a routine draw, the DVM didn't blink. She ran a fructosamine, the test that averages blood sugar over the past two to three weeks, and it came back normal. That's the standard move when a single glucose looks high on a stressed cat. A truly diabetic cat shows it on the fructosamine and usually on the urine too, not on one nervous morning's number.
Total protein splits into albumin and globulin. Albumin is made by the liver and lost through the kidneys or the gut. Globulin is the immune fraction and climbs with chronic infection or inflammation, including the feline retroviruses. The Merck Vet Manual is explicit that the ratio between the two is often more telling than either number alone.
Retrovirus status: FeLV and FIV
FeLV and FIV, feline leukemia virus and feline immunodeficiency virus, are the two retroviruses cats get tested for, usually with a quick in-house combo test rather than the main chemistry panel. A kitten gets tested before joining the household, and an adult cat gets retested after a fight wound, a new cat in the home, or any unexplained illness. A positive doesn't read the way owners often fear. Plenty of cats live for years with a known retrovirus status, and knowing it changes how the clinic reads everything else. A FeLV-positive cat with a low white count is a different conversation than the same numbers in a retrovirus-negative cat. If your cat's records include an old FeLV or FIV result, it's worth keeping, because it's part of how the next vet reads the next panel.
Reading a single panel versus reading a trend
A single panel is a snapshot. A trend is the story, and in cats the trend matters because the two big age-related conditions, kidney disease and hyperthyroidism, both announce themselves as drift before they announce themselves as a flag. A creatinine that's still inside the reference range but has climbed steadily over three years is more interesting than a one-time flag that was back to normal on recheck. The American Veterinary Medical Association's preventive-care guidance, which most clinics follow in some version, lands on annual bloodwork through adulthood and twice-yearly once a cat is senior, around eleven, partly so the year-over-year comparison even exists to read. Cornell's College of Veterinary Medicine says the same thing in its owner-facing material on senior cats. The math behind why senior visits matter so much is the same point the senior pet piece makes at length.
What to keep alongside the printout
The four things that make a cat's bloodwork printout useful at the next visit: the printout itself, the current food and any medications with doses and start dates, a note on appetite and water intake and litter-box changes in the two weeks around the draw, and the prior printout from the same lab. Cats make that last one harder than dogs, because a cat who hides illness also tends to get bloodwork less often, so the panels you do have are worth holding onto. If the household keeps records scattered across a shared email, a folder in a drawer, and a photo of a pill bottle on someone's phone, that's the starting point most families bring to the pet health records conversation. The same trend-reading logic applies to dogs, and the companion walk-through of a dog's bloodwork panel covers the canine side value by value.
Questions that come up reading a cat's panel
What is a normal BUN range for a cat?
There isn't one number to memorize. Every lab calibrates its own analyzers, and the reference interval printed next to the result is the band that lab considers normal for its patient population. A BUN from a clinic's in-house machine can read differently from a reference lab like IDEXX or Antech on the same cat drawn the same week. The comparison that matters is your cat's value against the range printed beside it, plus the trend across panels at the same lab. BUN also rises with dehydration and a high-protein meal, so a mildly high BUN with a normal creatinine and well-concentrated urine is usually less about the kidneys than the single number suggests.
Why is my cat's ALT high but the kidney values are normal?
Liver enzymes and kidney values move independently, so one being up while the other is fine is common and usually not alarming on its own. ALT rises for a long list of reasons, from a recent stretch of not eating to a medication effect to mild inflammation. A single mildly elevated liver enzyme on an otherwise clean panel is a flag for a recheck in a few weeks, not a diagnosis. The combination that changes the urgency is high liver enzymes plus a cat who has been skipping meals, because that raises the question of fatty liver, which is dangerous if it isn't caught early.
What does a low urine specific gravity mean in a cat?
Urine specific gravity measures how concentrated the urine is, which is one of the kidneys' main jobs. A healthy cat, built from a desert ancestor, normally makes very concentrated urine. When that number drops and stays down, especially alongside a creatinine or SDMA that's creeping up, it's one of the earlier signs the kidneys are losing the ability to concentrate. That's why a urine sample at the senior visit is worth asking about even when the blood chemistry looks fine, because the chemistry alone undercounts early kidney disease in cats.
What does the T4 number say about my cat's thyroid?
Total T4 measures the main thyroid hormone, and in cats the question is almost always whether there's too much of it. A high T4 in an older cat who is losing weight while eating well points toward hyperthyroidism, an overactive thyroid that's common in seniors. A normal T4 in a cat with strong symptoms isn't always the end of it, because another illness can mask the result, so a DVM may run a free T4 or repeat the test. A low T4 matters far less in cats than in dogs and is usually read in the context of other illness rather than as a thyroid problem of its own.
Is one flagged value on my cat's panel a problem?
Often not by itself. A flag means the result fell outside that lab's reference interval, not that it's clinically meaningful. By design, roughly one in twenty healthy patients lands outside any given range on any given test. The DVM reads the flag against the rest of the panel, the physical exam, your cat's history, and any prior results for trend. One mildly flagged value on a cat who looks and acts well usually earns a recheck, not a full workup.
How often should a senior cat get bloodwork?
The AVMA's preventive-care recommendations and most general-practice protocols land in the same place: annual bloodwork through adulthood, then twice a year once a cat reaches senior age, which is around eleven for most cats. The senior panels are where the most useful longitudinal reading happens, because comparing this year to last year at the same lab catches the slow drift that a single panel never could. A cat on a chronic medication gets a recheck schedule set by the drug, not by age.
Can the stress of the vet visit change my cat's results?
Some of them, more than in most dogs. Glucose can jump from the adrenaline of the car ride and the exam, sometimes into a range that would mean diabetes in a calm cat, which is why a single high glucose on a stressed cat is usually rechecked with a fructosamine rather than acted on. The white-cell count can shift into a stress pattern too, with high neutrophils and low lymphocytes. Most of the chemistry panel holds steady under stress, and a DVM reads the stress-sensitive numbers knowing how worked up the cat was on the table.
What does high phosphorus mean next to the kidney numbers?
Phosphorus tends to climb as kidney function falls, so a high phosphorus alongside a rising creatinine and SDMA is part of the chronic kidney disease picture rather than a separate problem. The International Renal Interest Society's staging uses phosphorus targets to guide diet and treatment at each stage, which is why your vet may raise a kidney diet or a phosphorus binder once the number starts to move. On its own, with normal kidney values, a single high phosphorus is often diet-related or a lab quirk and gets rechecked.
Read the page once, read the trend forever
A cat's panel is a snapshot of several systems on one morning, and on its own almost every line is ambiguous. Read against last year's panel and next year's, the same lines turn into signals the clinic can act on early: the kidney trend, the thyroid trend, the slow drift inside the normal range. The clinic reads the trend when the DVM pulls up the prior panel at the recheck. Most families don't have an easy way to do the same. The fix is small: keep every panel, keep it in one place, and bring it back. Call the clinic and ask what they want at the next senior visit, and bring the panels you've already got.
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Rachel Howland, CVT (ret.), spent a decade in clinic: seven years in a mixed practice in upstate New York, then three on the internal-medicine floor at Angell Animal Medical Center in Boston. She left practice in 2017 and has written about small-animal health since. She lives in Somerville with Juno, an 11-year-old hound mix managing chronic kidney disease, and Bishop, a Siamese cat. She does not diagnose or prescribe; she explains what your vet's records are telling you and what questions are fair to ask.