QUESTIONS

1. What is the predominating oxalate in oxalate cystic calculi?
    
2. The usual patient with oxalate cystic calculi is  male or female,  and a large dog or a small dog?
    
3. What 3 substances in urine will increase the tendency to form oxalate stones?
    
4. Vitamin B-6 has been advocated in the prevention of feline oxalate stones. Why is this?
    
5. Thiazide diuretics have been advocated in the prevention of oxalate bladder stones. Why is this?
    
6. The Select Care feline diets have citrates added with the idea of discouraging oxalate stone formation.  Why is this?
    
7. Another recommendation in the prevention of oxalate bladder stones is that Vitamin C be avoided.  Why is this?
    
8. What in the hell is Nephrocalcin?
    
9. EXTRA CREDIT:  Humans that get oxalate uroliths are told to stay away from foods containing calcium & foods containing oxalic acid.  The excretion of both will promote oxalate lith formation. The restriction of one without restriction of the other may lead to an increase in availabililty of the other.  What foods might these be?
   
   
   
   
    

ANSWERS

1. 50% are calcium oxalate monohydrate, 22% are calcium oxalate dihydrate & 28% are a mixture.
   
   
   
   
    
2. The usual patient w/oxalate cystic calculi is a male small dog.
   
   
   
   
    
3. Uric acid, calcium & oxalates in urine will tend to increase the incidence of oxalate liths.
   
   
   
   
    
4. There is an experimental population of cats that forms oxalate stones out of a true B-6 deficiency. Strange but true. This does not mean that B-6 will help a cat that has stones & no B-6 deficiency but it shouldn’t be harmful to try.  Vitamin B6 increases transamination of glyoxylate (precursor of oxalic acid) to glycine.  The idea is that w/o B6, glyoxylate will go to oxalic acid instead of to glycine.
   
   
   
   
    
5. Thiazides decrease renal excretion of calcium (and calcium in the bladder predisposes to oxalate stone formation).  But you must beware of hypercalcemia.  Thiazides also lead to K+ retention,too.
   
   
   
   
    
6. Citrates will complex with calcium in urine & form a salt which is much more soluble than calcium oxalate.  Citrates thus keep calcium away from oxalate.
   
   
   
   
    
7. Oxalic acid is an end product in the metabolism of ascorbic acid.  Just what you don’t need: more oxalate production.  It should be noted however that this kind of hyper oxaluria has not been totally documented in the dog.
   
   
   
   
    
8. Nephrocalcin is a large molecular weight protein in human urine that seems to minimize oxalate crystal growth. In humans that form oxalate stones, nephrocalcin is structurally different from normal.  It is thought that the story is similar in the dog.
   
   
   
   
    
9. Well, it is  a bit more complicated than just restricting calcium.  Carbohydrates will augment calcium absorption in the GI tract from any source so humans are told to avoid milk products so as to avoid both CHO (lactose) & calcium in the GI tract at the same time.  Foods high in oxalic acid = chocolate, beans, nuts, sweet potatoes, wheat germ, spinach & rhubarb).
   
   * Note since salt in the diet seems to encourage calcium excretion by the kidney, salt restriction is also a good idea, too.