Why vets reach for blood tests as cats age
An older cat can look entirely herself while organs inside are quietly working harder than they used to. Kidneys, liver and thyroid in particular can drift out of their healthy pattern long before weight loss, thirst or behaviour change gives the game away at home, and hands and eyes in a physical exam cannot measure how those systems are performing. For a senior cat it serves three purposes at once: it looks for early change while action is most useful, it establishes what is normal for this individual cat, and it makes future decisions safer — for example, knowing kidney and liver values before an anaesthetic or a new long-term treatment lets the vet plan around real information rather than assumption.
The core profile, explained in plain terms
A standard senior profile usually combines several panels. A complete blood count examines red cells, which carry oxygen and can fall with chronic illness, white cells, which reflect infection and inflammation, and platelets involved in clotting. The biochemistry panel looks at kidney markers, which rise when the kidneys are no longer filtering as effectively as they should; liver values, which can shift with liver strain or with illness elsewhere in the body; blood sugar, relevant to diabetes, which becomes more common in older, heavier cats; and proteins and salts that round out the picture of hydration and general condition. For senior cats a thyroid measurement is commonly added, because an overactive thyroid is a frequent condition of older cats and drives weight loss, restlessness and strain on the heart. Your vet may also suggest a urine sample alongside the bloods, since urine concentration helps interpret kidney results, and a blood pressure reading, which pairs with several of the same conditions.
Why your cat's own trend beats a single result
Laboratory results come with a reference range drawn from many cats, but the most sensitive comparison is your cat against herself last year. A kidney value that sits inside the printed range yet has climbed at every test for three visits tells a story a single normal result hides, and the same is true of slow falls in red cell counts or creeping thyroid values. That is the real argument for screening a well senior on a regular rhythm your vet sets: each test is partly a health check and partly the next point on a graph.
Preparing your cat for the blood draw
Ask the practice whether they want your cat fasted before the appointment, since food can affect some readings, and follow that instruction rather than a general rule. Keep the morning calm, use a familiar carrier, and tell the team if your cat finds restraint very stressful, because practices have ways to make blood sampling gentler and may plan the visit around a nervous patient.
What happens after the results come back
Expect the vet to talk you through findings in terms of what they mean for your cat specifically: all clear with a date for the next screen, a borderline value to recheck in a few months, or a change that prompts a closer look with further tests, a diet discussion or a management plan. A result outside the reference range is information, not a verdict, and many senior cats live comfortably for years with monitored, stable abnormalities once they are known and watched.
A file that makes the next test worth more
Screening only compounds in value when old results survive. Keep each printout with its date, note the practice that ran it if you ever change clinics, and store it alongside vaccination records and weight entries rather than in a message thread that will be lost at the next phone upgrade. Arranged in sequence in KinsLe's Pet Passport, those yearly blood results become the baseline chart your vet actually needs — proof of how your cat has changed, in numbers, across her senior years.