How to Detect Canine Bladder Stones
To detect canine bladder stones, start by watching for blood-stained urine, frequent urination, recurrent urinary infections, and signs of pain or strain while urinating. Some dogs may have a distended abdomen, so feel around its belly to see if it's swollen or hard. Your dog may also lick their penile tip, vagina, or belly excessively in an attempt to find relief from the inflammation and discomfort they're experiencing. If you notice any of these symptoms, it's best to take your dog to a veterinarian as soon as possible for an evaluation. Be sure to ask if you need to bring in a urine sample for analysis!
Watch out for blood-stained urine. Bladder stones rubbing against the delicate mucous membrane lining the bladder may cause it to become inflamed. When the bladder lining becomes inflamed it is prone to bleeding. This blood collects in the bladder and is passed out when the dog urinates. Stones that are smaller than the diameter of the urethra should pass out with no problems. Likewise, stones that are larger than the urethral diameter are too big to enter and hence cannot become stuck. Keep track of any recurrent urinary infections. An inflamed bladder has a weakened lining that is more vulnerable to infection. Many dogs with bladder stones get repeated urinary infections. Although antibiotics clear the infection, if the underlying cause - the trauma to the bladder lining - is still present, then the infection is likely to recur. Consider whether your dog is urinating more frequently. Inflammation affects not only the mucus membrane lining the bladder, but the nerves in the bladder wall. The inflamed nerves send an incorrect message to the brain that the bladder is full and needs emptying. This may result in the dog repeatedly trying to pass water even though their bladder is empty. See if your dog displays signs of discomfort when urinating. A dog with a sore bladder as a result of bladder stones will have discomfort when urinating. This may manifest itself as the dog looking wary as they pass water, or fidgeting, stopping mid-stream and seeking a new spot to lift their leg, as if the location is causing the problem. Unfortunately, there is a critical size when the stone fits into the urethra. It may then get trapped at anatomical narrowing where the urethra takes a U-turn around the brim of the pelvis, or at the penile tip. Both locations have a slightly reduced diameter and are a classic place for blockages to occur. Watch your dog while they try to urinate. Look for non-productive urination and repeated urinary straining. Like putting a plug in a sink, a trapped bladder stone stops the bladder from emptying out. The dog, knowing their bladder is full, tries to urinate but nothing comes out. As the bladder gets fuller, their determination to urinate increases, but to no effect.. The equivalent with the dog is the kidneys keep producing urine which fills the bladder. However, the bladder cannot overflow and so gets bigger and bigger. They are desperate to urinate and either squats, or lifts their leg, but when you examine the ground it is dry. The dog becomes obsessed by trying to urinate, repeatedly moving from spot to spot and lifting their leg. Take note if the dog is excessively licking their penile tip, vagina, or belly. Inflammation from the bladder lining can spread all the way down the urinary tract and some dogs lick their external genitalia in an attempt to alleviate their discomfort. If the bladder is hard and full, this is very uncomfortable and the dog will sometimes lick their abdomen over the bladder in an attempt to find relief. Examine your dog for abdominal distension. A large, hard bladder causes the dog's belly to distend. The bladder of a German Shepherd-sized dog can become football sized before it bursts, enough to visibly make their belly swell. Seek immediate veterinary attention if your dog collapses. If the dog cannot void urine, the waste products of metabolism build up in the bladder and reflux back into the kidneys. Many of these waste products are toxins - potassium can be especially dangerous. In blocked bladders, potassium reflexes into the bloodstream and high potassium levels can irritate the heart muscle and cause heart attacks, often with fatal consequences. Therefore if your dog collapses or you suspect its bladder has burst, it's essential that you rush him to the vets as quickly as possible. Bring your dog to the vet for testing. If you notice any of the above signs then contact your veterinarian. In order to decide what the problem is they may request a urine sample for analysis. The common tests done on urine are to measure specific gravity (how weak or strong the urine is), a dipstick test (which indicates if blood is present, checks for glucose, and protein content), and a sediment exam. The most helpful exam in determining the presence of bladder stones is the sediment exam. Understand how a urine sediment exam works. To prepare the sample, approximately 1ml of urine is put into a mini-test tube and spun down in a centrifuge. The heavy cells and sediment sink to the bottom under gravity. The liquid above the sediment is removed and the debris at the bottom of the tube tapped out onto a microscope slide. A drop of saline is added to the sediment to re-suspend it and help it to spread in a layer one cell thick over the slide. This is examined at under the microscope. The urine is examined for the presence of bacteria, red blood cells, renal casts, or crystals. Crystals are the precursors of bladder stones. It is unusual (but not impossible) for a bladder stone to form without crystals being evident in urine, and so their presence can be a warning sign of stones. If sediment exam reveals the presence of crystals, and the dog has a corresponding history suggestive of bladder stones, (see signs above) then further imaging is required in order to check for stones. Get a visual on the bladder stone using an ultrasound. The two options used to detect bladder stones are radiography and/or ultrasonography. However, not all types of stone show up on x-ray as some stones appear to have the same density as urine. Thus, ultrasound is arguably the more reliable diagnostic test. An ultrasound is a non-painful procedure which can be performed while the dog is conscious (in good-natured dogs). An area of fur is clipped from the area of the belly above where the bladder is located. The skin is cleaned and then a gel applied to the skin. The ultrasound probe is placed against the skin, the abdomen is scanned and the bladder identified. Fluid provides an a clear view for ultrasounds, so when bladder stones block the passage of ultrasound waves, they create an "acoustic shadow.” In real terms, this means there is a dark shadow on the far side of the stone, which can be seen regardless of the composition of the stone. Understand the problems with radiography. The drawback to radiography is that not all stones show up. If the mineral composition is of similar density to urine, then the stone will be invisible on a plain x-ray (one where no contrast agent is injected into the bladder). This can give false negative results. To avoid this, a double-contrast study may be done. This is where another agent, such as air, or a form of liquid barium, is introduced into the bladder. The aim is to provide material of a different radio density to urine, with the hope of showing up a stone. Unfortunately, even with double contrast studies occasionally stones can hide and evade detection, so more and more ultrasound is replacing radiography to detect stones. Be prepared for the possibility of surgery. Once a stone is found, the clinician needs to assess whether urgent action needs to be taken to avoid the risk of a urethral blockage. If this is likely, then surgery to remove the stone by colostomy (entering the abdomen and cutting the bladder open) is indicated, in order to get physical access to the stone and remove it. Change your dog's diet to prevent the formation of new stones. Once removed, the stone is sent to a laboratory for analysis. This gives the exact chemical composition of the stone, which helps in selecting a diet that is low in the constituent parts, and thus reduces the risk of the dog growing more stones in the future. 
Watch out for blood-stained urine. Keep track of any recurrent urinary infections. Consider whether your dog is urinating more frequently. See if your dog displays signs of discomfort when urinating. Watch your dog while they try to urinate. Take note if the dog is excessively licking their penile tip, vagina, or belly. Examine your dog for abdominal distension. Seek immediate veterinary attention if your dog collapses. Bring your dog to the vet for testing. Understand how a urine sediment exam works. Get a visual on the bladder stone using an ultrasound. Understand the problems with radiography. Be prepared for the possibility of surgery. Change your dog's diet to prevent the formation of new stones. 