Nephrolithiasis (Kidney Stones) in Cats
Dr. Bari Spielman
A complete blood count (CBC) may be within normal limits, although an elevated white blood cell count may be present, especially in those patients with associated pyelonephritis.
Certain diagnostic tests must be performed to diagnose nephrolithiasis and exclude other disease processes that may cause similar symptoms. A complete history, description of clinical signs, and thorough physical examination are all an important part of obtaining a diagnosis of nephrolithiasis. In addition, the following tests are recommended:
A biochemical profile may be within normal limits, but may reveal elevations in kidney enzymes or electrolyte abnormalities.
A urinalysis may reveal blood, white blood cells, protein, bacteria, crystals and/or white blood cell casts. The absence of any or all of these does not rule out nephrolithiasis.
A bacterial urine culture is performed to assess for the presence of a urinary tract infection, but may be negative in some cases.
Abdominal X-rays are often diagnostic for certain types of radiopaque stones that are clearly seen on X-rays. If they are within normal limits, that does not rule out the possibility of nephroliths.
Abdominal ultrasound is helpful in evaluating the kidney and confirming the presence, size, and number of nephroliths, in addition to assessing the rest of the urinary tract for stones. Additionally, characteristic changes are seen within the renal pelvis (inside of the kidney) that may be consistent with kidney infection. Ultrasound is a noninvasive procedure that often necessitates the expertise of a specialist and/or referral hospital.
Your veterinarian may recommend additional tests to exclude or diagnose concurrent conditions. These tests are not necessary in every case, but may be of benefit in certain individuals and are selected on a case-by-case basis. These include:
Excretory urography is an intravenous dye study that "lights up" the upper urinary tract (kidneys and ureters). It is very helpful in documenting stones in these structures, and may identify other abnormalities, such as pyelonephritis or ectopic ureters. Ectopic ureters are a congenital abnormality in which the ureter or tube that drains the kidney into the bladder joins the bladder in an abnormal position.
A bacterial culture of the kidney pelvis may be obtained with the guidance of abdominal ultrasound. This may be particularly important in the patient who has a negative urine culture obtained from the bladder.
If a stone or fragment of stone is available after it has passed into the lower urinary tract or even outside the body, because of natural circumstances or due to the intervention of extracorporeal shockwave lithotripsy (ESWL), it should be submitted for stone analysis. Stone identification may be of benefit in the treatment and prevention in the future.
Animals with inactive nephroliths that are not causing any clinical signs may not require therapy. They should be monitored periodically by urinalysis, urine culture, radiographs and/or ultrasound. Although some inactive stones may remain inactive for the duration of the individual's life, it is important to note that inactive stones may become active, causing severe clinical signs with very little warning. Equally important is choosing the most appropriate therapy for the patient who is having associated clinical signs. All recommendations by your veterinarian should be followed very closely, and any questions or concerns that arise during the treatment protocol should be addressed immediately.
Medical and/or dietary dissolution may be attempted. It is important for both you and your veterinarian to monitor your pet very closely during this period, as it is possible that not all stones can or will dissolve. The specific medication and/or diet will vary depending on the type of stone. As some stones are not available for analysis, it can be a guessing game, taking into account the size, shape, and visibility of the stones through the diagnostic work up.
If the patient is in kidney failure or is having severe clinical signs associated with the presence of the stones, their prompt removal is recommended.
Surgical removal necessitates a nephrotomy, or cutting into the kidney, to retrieve the stone. There are cases that might necessitate a nephrectomy, which is kidney removal. These are procedures that are associated with risk, and it is recommended that they be performed by an experienced individual.
Extracorporeal shock wave lithotripsy (ESWL) is a relatively safe and effective way of treating nephroliths in dogs, but it can only be performed at certain referral institutions. In this procedure, the stones are crushed in the bladder with shock waves and then the fragments are flushed out.
Antibiotic therapy is indicated in those patients with urinary tract infections.
Fluid therapy is indicated in those patients that are dehydrated, have severe infections or kidney failure.