Creatinine only rises after roughly 75% of kidney function is lost. SDMA rises as early as 25 to 40% of loss. That gap changes everything in chronic kidney disease screening.
What is SDMA?
SDMA (symmetric dimethylarginine) is a product of protein metabolism, eliminated almost exclusively by glomerular filtration. Unlike creatinine, it is not influenced by muscle mass: an old, cachectic cat, in whom creatinine is falsely reassuring, will see its SDMA faithfully reflect its kidney function.
When to test?
Three situations justify SDMA testing: early screening in the aging animal, as part of an annual geriatric work-up; monitoring a patient already IRIS-staged, to refine the stage; and exploring a borderline creatinine in a malnourished animal, where SDMA settles the question.
How to interpret it?
An SDMA above 14 µg/dl points to renal involvement. Between 15 and 19 µg/dl in an otherwise stable animal, re-check at a distance before concluding. Beyond that, involvement is confirmed, and SDMA helps re-position the IRIS stage, especially in the malnourished patient where creatinine underestimates severity.
What SDMA does not replace
It measures filtration and nothing else. A complete urinalysis remains necessary: specific gravity tells you whether the kidney still concentrates, the urine protein to creatinine ratio screens for proteinuria, and the sediment looks for infection or casts.
Blood pressure belongs to the same work-up. Hypertension often accompanies chronic kidney disease and damages the kidney, the eye and the heart without warning before the complication.
Three situations that mislead
Dehydration. Pre-renal azotaemia raises SDMA with no intrinsic kidney disease. In a dehydrated animal, repeat the test after rehydration before concluding.
Feline hyperthyroidism. It increases glomerular filtration and masks underlying kidney disease. A hyperthyroid cat with a normal SDMA may see its kidney function surface once the thyroid is treated.
Cardiac follow-up. NT-proBNP is also cleared by the kidney, so renal failure raises it with no heart disease; cardiac troponin I can rise moderately too. Reading kidney function and cardiac markers together avoids blaming the heart for what comes from the kidney.
Why run it in-house?
Outsourced SDMA comes back in three to five days. Three to five days during which the owner waits, and during which you cannot adjust management. Run on your bench, it is available during the consultation.
This is exactly the logic of the ImMScan analyzer: the tests you outsource — SDMA, T4, cortisol — become tests handed over at the front desk, in 3 to 15 minutes. The margin you left to the external lab stays with you, and the client leaves with a follow-up plan, not a promise of a callback.
In summary
SDMA is the early screening marker for kidney disease, insensitive to muscle mass, complementary to creatinine. Tested in-house, it transforms nephrology follow-up: an immediate result, an immediate decision, an owner reassured the same day.
Frequently asked questions
No, it complements it. Creatinine remains useful, not least for IRIS staging and for following a patient already known to you. SDMA supplies what creatinine cannot: earlier detection, and a value that does not depend on muscle mass.
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