Stones in the urinary tract are common in dogs and cats. Even though dogs and cats do get kidney stones, it is bladder stones that causes more problems. The medical term for bladder stone is urolithiasis or cystic calculi. We will use stone, calculi, and urolith synonymously in this page.
Stones can also occur in the kidneys, where they are called nephroliths. This page will limit its discussion to stones in the bladder.
There are several factor, usually working in combination, that lead to urolith formation:
Urine that is saturated with excess amount of certain minerals are prone to form bladder stones. These minerals commonly include magnesium, phosphorous, calcium, and ammonia. Most stones consist of an organic matrix of protein surrounded by crystalline minerals.
Diet can have a major impact here, and is one of the primary methods we use to treat and prevent uroliths.
pH is an indicator of acidity by measuring the hydrogen ion concentration. a pH of 7 is neutral. Below 7 is acidic, above 7 is alkaline. As a general rule, dog and cats tend to have an acidic urine normally. Some uroliths have a propensity to form in acidic urine while others tend to form in alkaline urine. Urine pH needs to be measure immediately upon voiding from the bladder for it to be accurate.
Some uroliths form due to the presence of bacteria in the urine, so control of these bacteria is important. Bacteria are diagnosed by culturing the urine or the inside of a stone after surgical removal. Normal urine is sterile, so any bacteria cultured from the urine is abnormal. When bacteria are cultured a pet has a urinary tract infection (UTI) and needs antibiotics. Common bacteria in UTI's include E. coli, Staph. spp., and Proteus.
If any bacteria are cultured in the urine our laboratory will test numerous antibiotics to determine which are the best ones to eliminate the bacteria. This is called sensitivity testing.
Liver shunts are an abnormality of blood flow to the liver. Blood that would normally flow through the liver now bypasses the liver. One of the many consequences of this disease, called Portosystemic shunts (PSS), is the formation of ammonium urate bladder stones.
Medications can predispose pets to forming bladder stones. Sometimes they do this by increasing the calcium level in the urine. Medications that increase or decrease the pH of the urine can also set the stage for stone formation. Some medications can actually cause formation of stones when used for long periods of time. The following list includes some of these medications:
Ascorbic Acid (Vitamin C)
Predisposing causes of bladder stones include pets that are not drinking enough or are not allowed to urinate frequently. Bacteria and stone forming chemicals stagnate in the urinary bladder and increase the chance of a stone forming. Mechanical flushing of the bladder, in the form of normal and frequent urination, will prevent this. Always make sure your pet has access to fresh water, changed several times per day, and the ability to urinate frequently. As a matter of fact, if you feed dry food you should be giving more than one cup of water per cup of dry food. An easy way to get around this important requirement for water is not to feed dry food at all. Your pet's urine should be clear, with no odor or color, and should be often. Sometimes these common sense suggestions are so obvious that we tend to forget about their importance.