High SDMA in cats: the marker that speaks before creatinine

What this marker measures

SDMA, or symmetric dimethylarginine, is a small molecule released continuously by every cell in the body as it renews its proteins. It is cleared almost entirely by kidney filtration. So its concentration in blood rises when the kidneys filter less well. Two features make it useful in cats. It depends very little on muscle mass, unlike creatinine, which matters in an older cat that has wasted. And it leaves the laboratory's reference range earlier in the course of things, at a stage when creatinine can still look normal.

What vets look into when the value sits outside the range

Ordered from the most common to the rarest.

In older cats, hyperthyroidism deserves a mention of its own. It increases the filtration rate and can mask kidney damage on creatinine. SDMA helps to see what is going on behind it.

What this value does not tell you on its own

SDMA says there is less filtration. It says neither why, nor since when, nor whether it is reversible. It is a screening signal, not a conclusion.

What is read at the same time:

• Urine specific gravity, on a sample collected before any fluids. Urine that is still well concentrated alongside a high SDMA changes the interpretation completely compared with dilute urine.
• Creatinine and urea, to place SDMA within a consistent whole.
• Hydration state on the day of the sample, plus weight and body condition compared with earlier visits.
• The urine protein:creatinine ratio and blood pressure, which weigh heavily on monitoring.
• Phosphorus, potassium and calcium.
• T4 in an older cat, and a full urine examination with dipstick, sediment and culture if the context justifies it.
• Ultrasound of the urinary tract, which shows the size and structure of the kidneys and looks for an obstruction.

Two reading habits. A value is only compared with the range printed on your report, because the result depends on the method and the laboratory. And a single value freezes one moment: it is the gap between two measurements made under similar conditions that carries guidance, not the isolated line. A rise confirmed on two samples in a properly hydrated cat does not carry the same weight as a rise seen once.

Questions to ask your vet

1. Is the SDMA raised in isolation, or are creatinine and urea moving the same way?
2. Has urine specific gravity been measured before any fluids, and what does it show?
3. Was my cat dehydrated on the day of the sample, and could that explain part of the value?
4. How soon should the test be repeated to confirm, and at the same laboratory?
5. Should T4, blood pressure and the urine protein:creatinine ratio be added to this panel?

High SDMA but normal creatinine, is that serious?

It is the commonest and most useful combination the marker gives. SDMA leaves the laboratory's range earlier than creatinine does, so this situation can correspond to an early fall in filtration. It can equally correspond to dehydration on the day or to a variation that needs confirming, hence the second sample.

Is SDMA more reliable than creatinine in a thin cat?

On that precise point, yes. Creatinine depends on muscle mass and underestimates loss of function in a cat that has lost weight, which is common in older cats. SDMA is far less sensitive to that bias, and that is its main reason for being on a panel.

Does a high SDMA mean permanent kidney disease?

No, not on a single measurement. The fall in filtration can be temporary, linked to dehydration or to an acute episode, and can return to normal. It is repeating the test later, on a hydrated cat, that separates lasting damage from a one-off event.