At the clinic where I work, we measure urine specific gravity and the total protein in blood serum. The usg refers to the concentration of the urine. I think the ideal USG is 1.020 or 1002. When my dog had struvite crystals, her USG was 1.070. You can buy those chemstrips which you dip in the urine and match the colours. This will tell you the ph as well as other information. Or buy ph strips.