In senior dogs, what clinical sign usually appears in Renal Insufficiency before azotemia develops?

• A. Hyperkalemia
• B. Proteinuria
• C. Hyposthenuria
• D. Isosthenuria

Answer: (D)

When renal function begins to decline, the kidneys’ ability to concentrate urine is one of the first functions lost. With fewer functioning nephrons, the tubules can’t create a highly concentrated urine, so the urine produced tends to have a specific gravity close to that of plasma. This is isosthenuria. It can be detected even while blood tests for waste products (azotemia) are still normal, making it a common early sign of renal insufficiency in senior dogs. As the disease progresses and GFR falls further, azotemia becomes evident and other changes, like potassium handling or proteinuria, may appear later. While very dilute urine (hyposthenuria) or proteinuria can occur, the hallmark early indicator before azotemia is isosthenuric urine.