In a cat with azotemia and hyperphosphatemia, which diagnostic test should be performed next?

• A. Urinalysis
• B. Abdominal ultrasound
• C. Serum glucose
• D. Complete blood count

Answer: (A)

Assessing kidney function and urinary tract involvement is the first thing to do when a cat has azotemia and hyperphosphatemia. A urinalysis provides essential information about how well the kidneys are concentrating urine, whether there is protein in the urine, and whether the urinary tract is inflamed or infected. The urine specific gravity shows if the kidneys can concentrate urine (isosthenuria suggests intrinsic kidney disease), while the sediment reveals casts, cells, crystals, or bacteria that point to tubular injury, nephritis, stones, or infection. Proteinuria and the presence of casts further support renal involvement and help distinguish different types of kidney disease. This functional and infectious/structural snapshot guides subsequent steps, including imaging or targeted therapy, and is faster and less invasive than starting with imaging alone. Abdominal ultrasound can be valuable for structural assessment, but urinalysis provides immediate, actionable information about renal health. Serum glucose and a complete blood count are less directly informative for this specific diagnostic direction in the context of azotemia with hyperphosphatemia.