Urinating Too Often?

My 3-year-old registered Paint gelding urinates up to three times in a three-to-four hour period. My veterinarian has checked a blood profile and two urinalyses. The blood profile was normal and the first urinalysis showed elevated protein. The second urine sample was normal. If we are still concerned about a kidney problem, what other tests can we do? Is there something else we should look for?    Andrea

 The normal urinalyses and blood work reported for your horse (other than the elevated protein value on the first sample) suggest that kidney function is adequate, urine concentrating ability is normal (as indicated by a urine specific gravity value greater than 1.012), and that there is no indication of infection (no increase in white cell count) or inflammation (no increase in red blood cells). This suggests that primary kidney disease is less likely. Urine protein analysis can yield a false positive due to the (normally) alkaline pH of horse urine, and the single positive value was probably not significant.

More useful information that would help characterize your observations would include the answers to the following:

  1. Is the increased frequency of urination associated with voiding a normal volume of urine in an appropriate amount of time?
  2. Does the horse seem to strain or appear painful during urination?

The voiding of small volumes of urine frequently (pollakiuria) can be associated with irritation of the urinary tract, which might result from problems such as blister beetle poisoning or bladder stones. Straining or pain associated with urination suggests partial obstruction or significant urinary tract inflammation, or can reflect injury to a body system other than the urinary system (i.e., gastrointestinal or musculoskeletal pain).

There is also the chance that the cause of the frequent urination will be inexplicable. You could end up spending a lot of time and money looking into this situation and see no results. So, it depends on how much money you are willing to spend to try to solve a problem that might have no solution.

Further evaluation of the urinary system would include thorough examination of the penis and external urethra, rectal examination (palpation of the bladder and left kidney), evaluation of fractional excretion of electrolytes (FE) and urine GGT/creatinine ratio, measuring of the gelding's 24-hour water consumption and urine production, ultrasonography of the kidneys, and endoscopy of the urethra and bladder.

The external urethra might be affected by tumors (squamous cell carcinoma) and insect-associated injury (Habronema infection), causing partial-to-complete obstruction of urine outflow.

Rectal examination can facilitate identification of bladder stones, dilation of ureters, changes in size or shape of the left kidney (the right kidney can't be reached on rectal examination), and, in some cases, pain from infection when the left kidney is palpated. Irritation of the urinary tract is most often accompanied by blood or an increased white cell count in the urine.

Fractional excretion of electrolytes (FE) and urine GGT/creatinine ratio should be evaluated in association with the routine urinalysis and serum chemistry panel. Abnormal FE values reflect abnormalities of renal tubular function. An abnormal urine GGT/creatinine ratio suggests renal (kidney) tubular damage.

For the average horse (weighing about 450 kg), normal water intake is 20-30 liters per 24 hours, depending on environmental temperature. Increased water intake can be psychogenic (not due to kidney dysfunction) or associated with primary kidney disease. Normal intake suggests that primary kidney disease is less likely. Primary kidney disease severe enough to cause increased water intake would likely be accompanied by structural changes in the kidneys and/or abnormal blood chemistry and urinalysis values.

Measuring 24-hour urine production can help characterize the increased urine frequency that you have observed. With normal urine output (five to 15 liters daily for an adult), primary kidney disease would be less likely. Unfortunately, 24-hour urine quantitation in the horse is not a simple task.

Abnormalities in size, shape, architecture, and echogenicity of the kidneys can be seen via ultrasonography. Increased kidney size often occurs in acute renal failure, when kidneys become swollen or edematous (fluid-filled). In chronic kidney disease, the kidneys shrink over time and can have cellular infiltrates that change their echogenic appearance. Kidney stones or sediment are visualized as hyperechoic (bright) densities within the kidney. In cases where the urine outflow has been obstructed, the kidneys become distended and might have cystic areas that appear hypoechoic (dark) on ultrasound evaluation.

Endoscopic examination of the urethra and bladder will identify urethral injuries, bladder stones, and abnormalities in the trigone area (where the ureters attach to the bladder). If urine is grossly abnormal, the source of the abnormal urine (i.e., the right or left ureter) can be seen by endoscopic examination of the bladder. 

--Thomas L. Seahorn, DVM, MS, Dipl. ACVIM, ACVECC; Janyce L. Seahorn, DVM, MS, Dipl. ACVA, ACVIM, ACVECC; Equine Veterinary Specialists, PLLC; Georgetown, Ky.

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