Cystinuria is an inherited, genetic disorder.  This is a condition where there is an excess of cystine in the urine.  There is an impaired ability for reabsorption of the amino acid, cystine in the kidney tubules.  Cystine is not reabsorbed by the kidneys therefore it becomes part of the kidney’s product :  urine.  Most of the time any excess cystine is excreted in the urine.   

Cystine is one of the sulfur-containing amino acids and may give the urine a ‘rotten egg’ smell or odor.  

Sometimes cystine will solidify and form stones, often referred to as crystals, uroliths, or calculi;  these are all interchangeable terms. 

Cystine stones cause problems by blocking the urethra, bladder or kidney, resulting in either prevention or slowing of urination, sometimes very painful.  There may also be blood in the urine caused by straining to urinate and also caused by the stones scratching the mucosal tissue.  Sometimes the stones, if small enough can be passed without incident, but in severe cases, the blockages can lead to rupture of the bladder or kidney, which could be fatal.  

Medical management :  is possible by drugs that will dissolve the stones.  The drugs do not prevent stones from forming but will ‘shrink’ those already formed in some cases.  Drugs also come with side effects. 

Surgery :  may be indicated although it has been noted that often stones will continue to form,  making surgery necessary again. 

Dietary management :  Cystine is NOT THE ENEMY- it is a necessary amino acid. It must be part of any diet and if cystine is lacking in diet, the body will manufacture cystine out of other amino acids (methionine).   Feeding a diet containing the lowest cystine containing source of foods is the best way. 

Cystine behaves differently from other forms or types of urinary stones, like struvites, in that they tend to form when the urine is acidic or has a low pH.  The goal in modifying the diet is to alkinalize or raise the pH of the urine.  This will be less likely to form into stones and more likely to be excreted as part of the urine in a normal fashion.  

High protein diets, bases on large quantities of meats leads to acidic urine. Low protein diets based on more plant materials lead to alkaline urine.  

One way to trick the urine into becoming more alkalinic is to use ‘buffering agents’.  These will react in the digestive sytem and internal organs to de-acidify or ‘buffer’ the urine components, resulting in maintaining the pH at a higher level, thus preventing stone formations.  The most common buffer is plain old baking soda (sodium bicarbonate). Some forms of Vitamin C will also help control the pH of urine too. 

Cystinuria can be controlled and managed ;  it doesn’t mean or have to be illness or death for your dog. Affected dogs should not be bred or artificially inseminated, since this is a genetic condition.