The question about false positives is here along with a lot of other information about this test. Vets don't, or should not, make all of their calls based on test numbers alone.
I had replied to the OP previously but missed that this was a puppy. In rereading it, I thought the vet said at this point it is not diagnosed as renal failure.
https://www.idexx.com/files/small-an.../sdma-faqs.pdf
A quote from the above:
• Microalbuminuria—Microalbuminuria is a urine test. It is
an early marker only in some cases of CKD. Physiologic
transient increases are common. It will also be positive with
urinary tract inflammation, so additional testing is needed
to rule out urinary tract infection, inflammation, or significant
hematuria. Once persistence has been established and
false positives eliminated, microalbuminuria will be the
earliest indicator of glomerular disease. In early glomerular
disease when GFR may still be normal, SDMA may also
remain normal. Similarly, microalbuminuria may be an early
indicator of some but not all tubulointerstitial CKD, and as
GFR decreases, SDMA will increase. A positive result should
always be followed by a UPC ratio testing to determine
quantitative value. It is common for the microalbuminuria test
and the UPC ratio to be normal, especially in early CKD.
9. Will SDMA replace creatinine in diagnosing CKD? Do I still
need to use creatinine if I have SDMA?
SDMA and creatinine are complementary. SDMA will not
replace creatinine; it is another more sensitive tool to evaluate
kidney function. A complete kidney evaluation should consist
of a thorough history, physical examination, and evaluation
of minimum database, including CBC, chemistry panel
with SDMA, and complete urinalysis. IDEXX will include the
SDMA kidney test in all routine reference laboratory chemistry
profiles this summer at no additional cost and with the same
turnaround time, so creatinine will be readily available for
comparison. Creatinine is needed for International Renal
Interest Society (IRIS) staging of CKD, so it will continue to be
important for clinical characterization of CKD patients