Chronic kidney disease progression in cats — monitoring labs
Wondering what a full interpretation looks like? See a sample report →
What Creatinine and SDMA Are Actually Measuring
Both creatinine and symmetric dimethylarginine, usually shortened to SDMA, are substances the kidneys are meant to clear from the blood. When the glomeruli – the tiny filtering units inside the kidney – filter less blood than they should, these substances build up, and the panel reports the rise. That is the whole basis of using them to monitor chronic kidney disease: a climbing creatinine or a climbing SDMA indicates decreased glomerular filtration, the gradual loss of filtering capacity that defines CKD. Neither value names the cause and neither, on its own, tells you the stage; they tell your veterinarian how much filtering work the kidneys are still doing, and following them across rechecks is how progression is actually tracked. The broader set of kidney markers a cat panel reports exists precisely because no single number captures the whole picture.
Why a Veterinarian Reads the Two Together, Not Apart
Creatinine and SDMA point in the same direction, but they have different blind spots, and that is exactly why they are interpreted side by side. Creatinine is produced by muscle, so its level reflects muscle mass as well as filtration: a thin, older cat that has lost condition can post a deceptively low creatinine even while its kidneys are struggling, because a low creatinine reflects reduced muscle mass rather than improved function. SDMA is far less swayed by muscle, and it tends to rise earlier in the course of declining filtration, which makes it a useful early marker of reduced kidney function – the reasoning explored further in what a high SDMA means in cats and in SDMA for early CKD detection. When one marker moves and the other lags, that mismatch is information in itself; an elevation in both creatinine and SDMA reads differently from a creatinine that has drifted down while SDMA stays up.
Where the Reference Line Sits
Reference intervals vary between laboratories because they depend on the analyser and method used, so the range printed on your own cat’s report is always the final word. As an evidence-based guide, the verified feline intervals for the markers most often followed in CKD are set out below. The renal markers sit at the top; the companions beneath them are listed because filtration markers are rarely judged in isolation from the values CKD tends to disturb.
| Parameter | Normal reference range (cat) | Role in CKD monitoring |
|---|---|---|
| Creatinine | 0.8-2.1 mg/dL | Filtration marker; influenced by muscle mass |
| SDMA | 0-14 µg/dL | Filtration marker; rises earlier, less muscle-dependent |
| BUN | 17-35 mg/dL | Supports the filtration picture; sensitive to hydration and diet |
| Phosphate | 2.6-5.5 mg/dL | A consequence of falling filtration that often guides treatment |
| Potassium | 3.8-5.5 mEq/L | Can shift as the kidneys handle electrolytes less well |
| Urine specific gravity | 1.035-1.060 | Shows whether the kidney can still concentrate urine |
See the full reference intervals for the cat — every value cited to the laboratory document or paper it came from.
A creatinine just outside the interval in a bright, well-hydrated cat and the same value in a dehydrated, unwell one are not the same finding, which is the whole reason these markers are read in context rather than against a fixed cut-off.
Reading the Trend, Not the Snapshot
In chronic kidney disease the single most informative number is often the one from the last visit, because what matters is the direction the values are moving. A creatinine that holds steady across several rechecks tells a calmer story than the same value reached by climbing steadily over months. This is why a first abnormal result is confirmed rather than acted on alone: a raised creatinine can be pre-renal – from dehydration, for instance – before it reflects the kidney itself, since increased creatinine indicates decreased glomerular filtration whether the cause is pre-renal, renal or post-renal. Sorting that out is part of the early blood-test interpretation a veterinarian works through, and the staging framework itself is laid out in how creatinine is interpreted under the IRIS scheme. The table below sketches how the same marker is weighed differently depending on what it is doing over time.
| What the trend shows | How the veterinarian tends to read it |
|---|---|
| Creatinine and SDMA both stable across rechecks | A reassuring plateau; the current plan is holding and intervals may lengthen. |
| SDMA rising while creatinine still looks normal | An early signal of falling filtration that warrants closer follow-up, as covered in SDMA changes and their causes. |
| Creatinine drifting down while SDMA stays up | Often muscle loss masking unchanged filtration, not improvement – the muscle blind spot in action. |
| Both climbing together over time | Progression; the plan is usually revisited, sometimes alongside a review of a combined BUN and creatinine rise. |
The Values That Travel Alongside the Filtration Markers
Creatinine and SDMA describe how much the kidney is filtering, but CKD also changes how the kidney handles other substances, and those shifts often shape how a cat feels and what treatment is added. Following them is part of monitoring, not a separate exercise.
| Read alongside creatinine and SDMA | What it adds |
|---|---|
| BUN | A second filtration signal, but one swayed by hydration, diet and gut bleeding, so it is weighed against the more specific markers and against the question of kidney disease versus hyperthyroidism. |
| Phosphorus | Tends to rise as filtration falls; managing it is a central part of slowing how a cat feels the disease. |
| Potassium | Can drift as the diseased kidney handles electrolytes less reliably, and is followed because it affects strength and appetite. |
| Urine concentration and protein | The urine side of the story – whether the kidney can still concentrate, and whether protein is being lost, both of which the blood markers cannot show, as set out in what to look for in kidney bloodwork. |
When several of these move at once, the interpretation tightens – a pattern taken further in how diet timing and phosphate binders fit in and in the routine annual senior-cat panel.
What Can Make the Picture Misleading
A few recurring situations can pull a CKD picture out of shape, and recognising them is part of reading the panel honestly. Dehydration can lift creatinine and BUN before the kidney itself has changed, which is why a value is rechecked once the cat is rehydrated rather than treated as the final word. Muscle loss can quietly lower creatinine over months, so a number that looks better can simply reflect a thinner cat – the reason senior creatinine and BUN trends are read with body condition in mind. And in older cats an overactive thyroid can both mask and worsen kidney readings, so a thyroid check often accompanies kidney monitoring; the interplay is part of why hidden hyperthyroidism is screened for in the same age group. Protein status matters too, and a falling albumin can add another layer to interpret. None of these change what creatinine and SDMA mean – they change how confidently a single reading can be trusted, which is again why the trend wins over the snapshot.
When a Change Should Not Wait
The kidney numbers themselves are rarely the emergency; the cat’s condition is. Seek prompt veterinary care if a cat with known CKD stops eating, becomes noticeably more lethargic, vomits repeatedly, drinks and urinates far more or far less than usual, or seems weak or unsteady. A sudden jump in creatinine between rechecks, rather than the slow climb expected in chronic disease, also deserves quick attention, because it can signal something acute layered on top of the chronic problem. Appetite carries particular weight in cats: a cat that has gone off its food needs to be seen rather than watched, both for its own sake and because falling intake can itself accelerate decline. These are the moments when the monitoring plan stops being routine and the cat needs to be examined.
What Monitoring Is Trying to Achieve
There is no treatment aimed at the creatinine or SDMA number itself; the work is to manage the disease behind them and to catch change early. Chronic kidney disease is generally not reversible, so the goal of monitoring is not a normal result but a stable one – a trend that holds steady while the cat eats, drinks and behaves well. Depending on the stage and on what the wider panel shows, a veterinarian may adjust diet, address phosphorus, support hydration, or treat an electrolyte shift, and the recheck interval is set and then revised as the trend becomes clear. A newly diagnosed or unstable cat is usually seen more often than one that has plateaued for months. The combination of filtration markers, urine findings and the values that travel with them is what lets those decisions be made for the individual cat rather than from any single figure – the integrated reading laid out across the full kidney-marker overview and revisited at each visit.
What Changes When the Disease Moves a Stage
Monitoring chronic kidney disease is not a matter of watching one number climb. Each stage brings a different set of questions, and the panel is chosen to answer the questions that belong to where the cat is now. Early on the work is confirmation and baseline: repeat samples taken wh