1 yr old pup with kidney problems, Help,pls

Hi, to All. My 1 yr old large mixed breed dog was tested recently as had one bout of bright red diarrhea, then became normal. A few days later my vet performed fecal sample -all good. Then did blood work and pee sample which both showed high elevations of creatinine – both 108 and normal is 105. They are doing an abdominal ultrasound and re-test for lymes next week. Any thots on this or has anyone experienced this with such a young pup? Pls. Advise. Most Sincerely, Melinda..Am Worried.