RESULTS: Sprite has an infection in his kidneys, which is common for dogs dealing with kidney failure, so he's now on antibiotics. It could easily recur, and then we'd have to take other steps.
MORE LIVES THAN A CAT:
He also seems to have more lives than a cat! Several times over the last year we thought he wouldn't be with us much longer, and now he's used up another "life" (and of course we're so happy that he's got something that can be dealt with for now).
It turns out that when kidneys are failing they tend to cause infections. So, we're treating the infection with antibiotic. He hasn't had any accidents in the house in the last couple of days, so that's a good sign. We honestly don't know how long he'll be with us, given his condition and advanced age, but as long as he's not in pain, we're happy.
FYI - INFO ABOUT TESTING:
If you have a dog, and you don't know what that is, now you will. The most common blood tests used to diagnose kidney disease are Creatinine and BUN (also called Urea Nitrogen). However, several other standard blood test results also provide information about kidney disease, including Phosphorus, Calcium, and the Sodium:Potassium ratio.
WHAT IT MEANS: When creatinine is elevated above the normal range (usually around 1.6 mg/dL, or 141 µmol/L), this generally means that there is a problem with the kidneys.
EARLY KIDNEY FAILURE LEVELS: In general, creatinine values up to around 2.0 (177 µmol/L) are indicative of mild, or early stage, kidney disease
MODERATE KIDNEY FAILURE LEVELS: Values from around 2.0 up to about 5.0 (177-442 µmol/L) are more significant, but it is still likely that your dog may not be showing any symptoms
SEVERE KIDNEY FAILURE: Values above 5.0 (442 µmol/L) indicate more severe kidney failure, and are often accompanied by clinical signs such as vomiting and lack of appetite. At this stage, fluids can be very important, especially when your dog is vomiting, and your dog may even need to be hospitalized for IV fluids (I personally feel it is best to bring them home at night, even if they need to stay at the vet's during the day, if at all possible). Antacids (Pepcid, Zantac or Tagamet) and Carafate (anti-ulcer medication) should be given, along with Reglan (metoclopramide) for vomiting if needed, with your vet's approval.