A senior blood panel can look surprisingly intimidating when it lands on a veterinary bill. There may be dozens of abbreviations, several numbers marked “H” or “L,” and a handful of values that sound as though they belong to a medical chart rather than the dog or cat sitting beside you. The useful way to read that report is not to hunt for one “bad” number, but to understand what each group of values is trying to tell your veterinarian.
That distinction matters because bloodwork is rarely a diagnosis by itself. A chemistry panel, complete blood count, thyroid test, urinalysis, physical examination, blood pressure reading, symptoms at home, and previous results often work together. AAHA’s senior-care guidance recommends regular CBC, chemistry, and urinalysis testing for senior dogs and cats, commonly every 6 to 12 months, with thyroid screening also recommended on a regular basis.
First, Understand What the “Normal Range” Means
Every laboratory report includes a reference interval, usually printed beside the result. A value inside that interval is not a guarantee that an organ is healthy, and a value slightly outside it does not automatically mean disease. Laboratories use their own instruments, methods, and reference populations, so the range printed on your pet’s report is the one your veterinarian will use rather than a number copied from another clinic or found online.
The small H and L flags are best treated as attention markers, not severity labels. A result just outside the reference interval can sometimes have much less medical significance than a value that is still technically “normal” but has been steadily moving in the wrong direction for several years. This is one reason we have always found it helpful to keep copies of older senior panels instead of looking at each appointment as an isolated event.
Kidney Numbers: BUN, Creatinine, SDMA, Phosphorus, and Urine
Kidney assessment is one of the areas where pet owners most often focus on a single number, usually creatinine. In reality, kidney health is better judged by a group of findings that may include blood urea nitrogen (BUN), creatinine, SDMA, phosphorus, electrolytes, urine specific gravity, urine protein, blood pressure, hydration status, and the pet’s history. AAHA specifically encourages watching trends in SDMA, creatinine, and urine specific gravity in senior patients.
BUN is a waste product related to protein metabolism that is removed through the kidneys. A high BUN can occur with reduced kidney filtration, but it can also rise with dehydration, certain dietary factors, gastrointestinal bleeding, and other non-kidney influences. That is why a veterinarian usually does not see “high BUN” and immediately label the pet as having chronic kidney disease.
Creatinine is another waste product used as an indirect measure of kidney filtration. It is generally more useful than BUN for estimating filtration, but muscle mass matters. A heavily muscled dog can have a higher baseline creatinine, while an older cat or dog who has lost substantial muscle may produce less creatinine and appear better on paper than the kidneys actually are.
SDMA, which stands for symmetric dimethylarginine, has become a useful companion to creatinine because it is less influenced by loss of lean muscle mass. Veterinary guidance recognizes that SDMA can become abnormal when kidney filtration has declined even though creatinine remains within the laboratory interval. Chronic kidney disease staging is performed after kidney disease has been established, and IRIS recommends interpreting creatinine or SDMA in a stable, hydrated patient along with other findings rather than treating one result as a stand-alone diagnosis.
Urinalysis is especially valuable because blood and urine tell different parts of the kidney story. Urine specific gravity shows how concentrated or dilute the urine is, while protein, glucose, blood, sediment, and signs of infection can add context that a chemistry panel cannot provide. A senior cat with rising creatinine and increasingly dilute urine gives the veterinarian a different picture than a mildly elevated creatinine in a dehydrated patient whose urine remains appropriately concentrated.
Phosphorus often receives more attention once kidney disease is established or suspected. As kidney filtration declines, phosphorus may increase, especially in more advanced chronic kidney disease, but its meaning depends on the rest of the panel and the stage of disease. This is another place where trends over time are often more informative than one isolated number.
Liver Numbers: ALT and ALP Are Not the Same as “Liver Function”
The liver section of a chemistry panel causes a lot of unnecessary panic because the most visible values are often labeled “liver enzymes.” ALT, or alanine aminotransferase, can rise when liver cells are injured or their membranes become more permeable. An elevated ALT tells the veterinarian that liver-cell injury may be occurring, but it does not by itself identify the cause, measure the liver’s remaining capacity, or prove that the pet is in liver failure.
ALP, or alkaline phosphatase, is even more dependent on species and context. In dogs, ALP can increase with bile-flow problems, liver changes, steroid hormone effects, some medications, and other conditions, which makes it a sensitive but relatively nonspecific marker. Cats have much less circulating ALP activity than dogs, so even smaller elevations may receive more attention from a veterinarian.
Bilirubin is a different kind of clue. It is a pigment processed and excreted through the liver and biliary system, and an increase may occur with red blood cell destruction, liver disease, or impaired bile flow. Albumin, cholesterol, glucose, clotting measurements, and bile acids may also help a veterinarian assess what the liver is actually doing rather than simply whether liver-associated enzymes are leaking into the bloodstream.
The pattern often matters more than the presence of a single red flag. Veterinarians look at which enzymes are elevated, how far above the reference interval they are, whether they are rising or falling on repeat testing, what medications the pet receives, and whether other findings such as bilirubin changes or imaging abnormalities are present. Merck’s veterinary guidance specifically emphasizes the magnitude, pattern, and change over time when liver enzyme abnormalities are evaluated.
Thyroid Results Mean Different Things in Cats and Dogs
A T4 result deserves very different interpretation depending on whether the patient is a cat or a dog. Older cats are commonly screened for hyperthyroidism, a condition in which thyroid hormone production becomes excessive. Total T4 is a standard first-line test, and most hyperthyroid cats have an elevated T4, although some affected cats can have a value that falls within the laboratory reference interval.
That borderline situation is one reason veterinarians sometimes repeat T4 or add free T4 and TSH testing. Other illnesses, medications, nutrition, kidney disease, and liver disease can influence thyroid measurements, so the laboratory result has to fit the physical examination and the signs seen at home. Weight loss despite a good appetite, increased thirst, increased urination, vomiting, diarrhea, or unusual activity may add useful context in a cat, but those signs still do not diagnose hyperthyroidism on their own.
Dogs present almost the opposite thyroid problem. Hypothyroidism, meaning insufficient thyroid hormone, is much more common in dogs than cats, but a low total T4 alone is not enough to diagnose it. Illness elsewhere in the body, age, breed, and several medications can suppress T4 in dogs whose thyroid glands are functioning normally, so veterinarians may interpret total T4 together with free T4, TSH, clinical signs, and other laboratory findings.
This is a good example of why simply comparing a number with the printed range can mislead an owner. A low T4 in a sick older dog may mean something quite different from the same result in a dog with compatible symptoms and supporting thyroid tests. The question to ask is not just, “Is the T4 low?” but, “Does the veterinarian think this result represents thyroid disease, or could something else be affecting it?”
Glucose: A Snapshot That Needs Context
Blood glucose is one of the easiest numbers to understand conceptually because it measures the concentration of glucose circulating in the blood at that moment. It is also one of the easiest values to overinterpret. Food intake, stress, illness, medications, diabetes, and the circumstances surrounding the blood draw can all affect the result.
Cats deserve special caution here because veterinary stress can produce temporary hyperglycemia. Current AAHA feline diabetes guidance states that diagnosis requires evidence of sustained hyperglycemia, using findings such as repeat hyperglycemia or glucosuria outside a stressful setting, or increased glycated proteins such as fructosamine. Merck likewise describes persistent hyperglycemia and glucosuria as the basis of diabetes diagnosis rather than a single elevated blood glucose reading.
Fructosamine gives a longer view than a spot glucose measurement because it reflects glucose attached to circulating proteins over recent days. The 2026 AAHA feline diabetes guidelines describe it as reflecting average blood glucose over roughly the previous 7 to 10 days in cats, although other medical conditions can affect the result. Even fructosamine is not interpreted alone, which is why glucose patterns, urine findings, body weight, appetite, thirst, urination, and clinical signs still matter.
For people already caring for a diabetic pet, this distinction becomes very familiar. A single clinic glucose value may not resemble the pattern seen during a home curve or continuous glucose monitor session, particularly in a stressed cat. Any decision about insulin belongs with the veterinarian and should be based on the monitoring method, symptoms, eating pattern, and overall data rather than an isolated number on a routine senior panel.
The Most Useful Number May Be the One That Changed
Senior bloodwork becomes much more useful after a pet has accumulated a history. A creatinine result that has moved gradually from the low end of normal to the high end over several years may deserve attention even before it crosses the laboratory cutoff. The same principle applies to glucose, liver enzymes, thyroid hormone, body weight, urine concentration, and many other measurements.
This is why baseline testing in a healthy older pet has value beyond looking for disease on that particular day. AAHA recommends regular laboratory evaluation in senior dogs and cats partly because repeated testing gives the veterinary team a way to recognize change over time.
We have found that keeping a simple folder, spreadsheet, or printed chart of older results makes veterinary conversations easier, especially once a pet has several conditions and several specialists or clinics involved. Recording the date, body weight, major laboratory values, medications, appetite changes, drinking, urination, vomiting, stool changes, and any unusual behavior can turn a stack of reports into a usable medical history.
Questions That Make a Bloodwork Discussion More Useful
A flagged value is much easier to understand when the veterinarian explains what it means in relation to the rest of the panel. Owners can get a clearer picture by asking a few direct questions during the appointment:
- Which results concern you, and which are only mildly outside the reference interval?
- Is this value new, or has it been changing over time?
- Do the blood results match the urinalysis, blood pressure, physical examination, and symptoms?
- Could dehydration, medication, stress, diet, or another illness be influencing this number?
- Do you want to repeat the test, add another laboratory test, or consider imaging?
- What changes at home would make you want to see my pet sooner?
Those questions help separate “abnormal on paper” from “medically significant for this particular animal.” They also give the owner something concrete to watch between visits instead of leaving the clinic with a page full of unexplained abbreviations.
When a Lab Result Should Not Be Watched Casually
Many mild abnormalities can be rechecked on a schedule chosen by the veterinarian, but the animal’s condition always matters more than the color of the flag on the report. A senior dog or cat who is repeatedly vomiting, refusing food, becoming markedly weak, collapsing, struggling to breathe, unable to urinate, having seizures, or showing pronounced dehydration or yellow discoloration of the gums, eyes, or skin needs prompt veterinary assessment even if yesterday’s laboratory changes looked modest.
The reverse is also true. A pet who seems comfortable and stable can still have an early change worth investigating, which is one reason routine senior screening can find problems before they become obvious at home. Bloodwork works best as part of an ongoing conversation between what the laboratory measures, what the veterinarian finds, and what the person living with the animal notices every day.
Keep the actual reports whenever possible, not just the invoice showing that “senior bloodwork” was performed. On the next visit, bring the previous results and ask the veterinarian to point out the trends that matter, explain which values belong together, and tell you what would change the follow-up plan. Over years of caring for older and medically complicated animals, that habit has repeatedly made laboratory numbers feel less like mysterious codes and more like what they really are: pieces of a larger clinical picture.