Diet and Uroliths

Question 1

Define urolithiasis

Answer 1

the production of calculi in the kidney (nephrolithiasis), ureter (ureterolithiasis) or bladder (cystolithiasis)

Question 2

How do stones form ?

Answer 2

Normal colloids and crystalloids that are dissolved in solution in urine crystalise due to a high saturation of urine. This leads to the formation of the stone and is called nucleation.

They form on the surface of RBCs and epithelial cells.

The stones start to precipitate, with the saturation depending on urinary pH, solute concentration and complexation.

As they grow, more crystals are added to the nucleus, sticking together in the stage aggregation.

Question 3

Name some types of stones, and why do we have different types of stone ?

Answer 3

Oxalate
Struvite
(urate, cystine, silicate, calcium phosphate, calcium carbonate)

type of stone produced depends on urinary pH
- acidic pH = oxalate, uric acid and cystine
- alkaline pH = struvite, calcium carbonate and calcium phosphate

Question 4

Describe some risk factors for CaOx formation in dogs

Answer 4

> 7 years
neutered
male
cytitis
acidic urine pH
presence of RBCs or WBCs in urine
high protein in urine
smaller BW
obesity
low calcium and high oxalate diet
unbalanced phosphorous
antibiotics

^ Oxalobacter formingens is a Gram- anaerobic bacterium that degrades oxalate in the normal GI. Any form of antibiotics could lead to the absence of the bacteria, and hence an increase in gut oxalate levels, leading to stone formation.

Question 5

Describe some risk factors for struvite stones in cats.

Answer 5

alkaline pH
increased Mg, ammonium and P in urine
diets high in Mg, P, Ca, Na, Cl and fiber
hypermagnesuria
low dietary moisture
obesity
UTIs due to urease positive bacteria