SDMA (symmetric dimethylarginine) is a blood test used to detect kidney disease in cats, often catching it months or even years before older tests like creatinine show a problem. A normal SDMA level in cats is 14 µg/dL or below, and anything persistently above that suggests the kidneys aren’t filtering as well as they should be.
How SDMA Works as a Kidney Marker
Every cell in your cat’s body with a nucleus produces SDMA as a natural byproduct of protein metabolism. Once released into the bloodstream, SDMA is almost entirely removed by the kidneys through filtration. This makes it a remarkably clean indicator of kidney function: when the kidneys slow down, SDMA accumulates in the blood in a predictable way.
What makes SDMA particularly useful is what doesn’t affect it. Creatinine, the traditional kidney marker, is produced by muscle. As cats age and lose muscle mass, their creatinine levels actually drop, which can mask kidney problems. A thin, elderly cat with significant kidney disease might have a perfectly normal creatinine reading simply because the cat doesn’t have enough muscle to produce much of it. SDMA doesn’t have this blind spot. In a study comparing the two markers in geriatric cats, cats older than 15 had lower creatinine than younger cats (due to muscle wasting) but higher SDMA, accurately reflecting their declining kidney function. SDMA is not affected by lean body mass at all.
Why SDMA Catches Kidney Disease Earlier
Creatinine typically doesn’t rise above normal until a cat has lost roughly 75% of kidney function. SDMA is far more sensitive. Research from a 2014 study found that SDMA exceeds its normal range when kidney filtration drops by approximately 24 to 30% from normal, with 100% sensitivity and 91% specificity for detecting that level of decline.
In practical terms, this translates to a significant head start. Cats with chronic kidney disease (CKD) show elevated SDMA an average of 17 months before creatinine rises above normal. That’s over a year of lead time where dietary changes, hydration support, and closer monitoring could slow the disease’s progression.
What Normal and Abnormal Levels Mean
The reference ranges are straightforward:
- 14 µg/dL or below: Normal kidney function.
- 15 to 17 µg/dL: Mildly elevated. Under the International Renal Interest Society (IRIS) staging system, cats in this range with other evidence of kidney issues are classified as Stage 1 CKD, the earliest stage.
- Above 17 µg/dL: More significant. Some cats with SDMA in this range still have normal creatinine, which is exactly the scenario SDMA was designed to catch. IRIS classifies these cats as Stage 2 CKD even if creatinine looks fine.
- 20 µg/dL and above: Generally warrants more thorough investigation and closer follow-up.
Most cats with early kidney disease fall in the 15 to 20 µg/dL range. A single elevated reading isn’t always cause for alarm, though. Dehydration, a recent illness, or lab variability can temporarily push the number up. Vets typically want to see a persistently elevated SDMA, confirmed on a repeat test, before diagnosing CKD.
What Happens After an Elevated Result
If your cat’s SDMA comes back high, your vet will likely recommend a few follow-up steps rather than jumping to a diagnosis. A urinalysis is usually first. Urine concentration (specific gravity) tells your vet whether the kidneys are still able to concentrate urine properly. Dilute urine alongside elevated SDMA is a strong signal of kidney trouble. Your vet may also check for protein in the urine using a urine protein-to-creatinine ratio, since leaking protein is another hallmark of kidney damage.
Beyond urine testing, common follow-ups include blood pressure measurement (kidney disease often raises blood pressure in cats), abdominal imaging such as ultrasound to look at kidney size and structure, and trending other blood markers like BUN and phosphorus over time. For mildly elevated SDMA in the 15 to 19 range, this workup may happen at a routine recheck. For values of 20 or higher, most vets will want to investigate more promptly.
The key word is “trended.” A single snapshot matters less than the pattern over weeks and months. Your vet will likely want to recheck SDMA, creatinine, and urinalysis at regular intervals to see whether values are stable or climbing.
SDMA and Hyperthyroidism
Hyperthyroidism is extremely common in older cats, and it complicates kidney testing in a sneaky way. An overactive thyroid increases blood flow through the kidneys, which can artificially inflate filtration rates and make kidney values look better than they really are. Many cats diagnosed with hyperthyroidism are found to have underlying kidney disease once the thyroid condition is treated and blood flow normalizes.
Research on hyperthyroid cats treated with radioactive iodine showed that both SDMA and creatinine rose after treatment, reflecting the true (lower) kidney filtration rate once the thyroid was no longer masking it. Importantly, SDMA did not correlate with thyroid hormone levels themselves, only with actual kidney function. This means SDMA changes in hyperthyroid cats reflect real shifts in kidney performance rather than a direct effect of thyroid hormones on the test.
Limitations Worth Knowing
SDMA is a better kidney marker than creatinine in most situations, but it’s not perfect. It can fluctuate between blood draws, and not every elevated result means CKD. Acute illnesses, dehydration, or other temporary drops in kidney perfusion can raise SDMA without permanent kidney damage being present. That’s why persistent elevation, confirmed on at least one retest, is the diagnostic standard.
SDMA also doesn’t tell your vet what’s causing kidney problems, only that filtration has declined. Identifying the underlying cause still requires the full workup: imaging, urine culture, blood pressure, and sometimes infectious disease testing. Think of SDMA as an early alarm system. It’s excellent at sounding the alert, but your vet still needs to investigate what triggered it.