Lisa is correct that dogs in the early stages of Fanconi Syndrome spill intermittently. Spilling sugar is spilling sugar. If they are not spillng this week but were last week.. does NOT mean they are no longer afflicted.
It is imperative that your vet listen to you and not tell you that the intermittent spilling of sugar is NOT consistent with Fanconi Syndrome. Spilling sugar is NOT normal for a dog.
Any deviation from the test-strip should be considered as spilling sugar. An appointment with the vet should be scheduled and tests need to be run: Venus Blood Gas panel, CBC, Urinalysis.
Download the current protocol to give to your vet from the BCOA website (www.basenji.org).