Collecting urine samples

Advantages and disadvantages of different methods for urine collection

Method Advantages Disadvantages
Free catch

No risk (eg, trauma, bacterial infection) to animal.

Avoids iatrogenic hematuria.
May contain debris (eg, bacteria, exudate) from lower urinary and genital tract. If bacterial growth appears on urine culture, must differentiate between urethral contamination and urinary tract infection. Quantitative urine culture required.

Manual compression

Provides method for obtaining urine sample when voluntary micturition has not occurred.
May induce trauma to urinary tract, resulting in hematuria. May be stressful for animal, especially if bladder is painful. If bacterial growth appears on urine culture, must differentiate between urethral contamination and urinary tract infection. Quantitative urine culture required

Catheterization

Provides method for obtaining urine sample when other methods of collection have failed.
Potential for trauma to urinary tract, especially bladder. More invasive than other methods; sedation may be required. Risk of introducing bladder infection. If bacterial growth appears on urine culture, must differentiate between urethral contamination and urinary tract infection. Quantitative urine culture required. Least desirable method of urine collection.

Cystocentesis

Preferred method of collection for urine culture.
Easy to perform with ultrasound

Avoids contamination of sample from lower urinary tract.

Potential risk of trauma if performed incorrectly or patient moves during procedure. More invasive than spontaneous micturition. Potential for contamination of sample if needle penetrates colon during procedure.

Tests of Urinary Tract function

X-rays and ultrasound can tell us about the size and shape of the kidney and bladder. We can see cysts and uroliths. Injecting air or contrast into the bladder allows us to see much more detail about the bladder, highlighting abnormalities in position, tumors, and stones = contrast radiography. Air gives negative contrast by showing up black on an x-ray and iodine is a positive contrast showing up white on an x-ray. Using both together is called double contrast radiography. We can inject dye into the blood stream allows us to see the position of the ureters = IUV intravenous urethrogram. These tests are useful to investigate incontinence.

Blood tests – there is no single test that will give a definitive answer about the function of the kidneys we need to consider the results of several test and draw conclusions.

BUN – The Blood Urea Nitrogen (BUN) test is a measure of kidney function. Urea Nitrogen is naturally produced through the breakdown of proteins. The urea is excreted through the kidneys, so reduced kidney function will result in an elevation of the BUN. This test is not very specific for kidney disease in that dehydration and high protein diets will also cause elevations of the BUN. The BUN is best evaluated in conjunction with the blood creatinine, and results of a urinalysis to better evaluate your pet’s condition.

CREATININE – This is an amino acid that is normally released at a very constant rate from the cells of the muscles. Once in the blood, the kidneys remove it and excrete it in the urine at a very constant rate. The blood level of creatinine can be used to determine the functional capability of the kidneys. Elevations in the creatinine usually indicate a diminished kidney function. Even small elevations are usually significant.

TOTAL PROTEIN – The sum of the albumin, which is produced in the liver, and globulin, which are antibodies. Low total protein can be caused by starvation, liver disease, kidney disease or blood loss. Elevations in total protein are usually the result of dehydration, but also may be due to chronic infection or some tumors.

AMYLASE – The Amylase test determines the level of amylase in the blood. Amylase is stored in the pancreas and is normally released into the lumen of the small intestine shortly after a meal to help with the digestion of food. Amylase elevation may also be caused by a decreased kidney function; therefore, in the absence of illness typical for pancreatitis, evaluation of kidney function is warranted.

Urine Chemistry

  • Glucose is not normally present in the urine and its presence indicates diabetes.
  • Protein is not normally present in the urine. It’s presence may be due to kidney disease, inflammation in the urinary tract or infection. If elevated, examination of the urine for microalbumin is recommended to rule out kidney disease
  • Ketones are chemical by-products of fat metabolism. Ketosis is the term we use to denote excessive ketones. Ketosis develops in diabetes because glucose metabolism is altered due to the lack of insulin. When glucose cannot be used for energy, fat is burned for energy generating ketones and possibly ketosis. The most common causes of excessive ketones in the urine are diabetic ketoacidosis, starvation, low carbohydrate diet, high protein diet, and prolonged low blood sugar. Additional tests may be necessary or if the pet is showing signs of illness, we may need to hospitalise and administer immediate therapy to reduce these toxic by-products.
  • Bilirubin is a pigment that comes from the breakdown of haemoglobin in red blood cells. This pigment is then passed through the liver and becomes a part of the bile. Excessive production of this pigment may occur if the pet has haemolytic anaemia (a condition where red blood cells are being destroyed) or liver disease. Further testing may be necessary to determine the cause of condition.
  • Urobilogen is a colorless compound formed in the intestines by the reduction of bilirubin. Small amounts of bilirubin produced in the body by the breakdown of haemoglobin are excreted in the urine as urobilinogen. Increased amounts of urobilinogen in the urine indicate an excessive amount of bilirubin in the blood, which can mean disease and/or problems exist with the internal organs and further testing is recommended.

Specific Gravity

This is a measure of urine concentration. A high specific gravity is caused by dehydration. Low specific gravity indicates dilute urine and can be caused by diuretics, kidney disease, diabetes insipidus or psychogenic (excessive) thirst. Further tests including a water deprivation test are required to pinpoint the cause.

pH

This is a measure of how acidic the urine is. Less than 7 is acid, 7 is neutral and over 7 is alkaline. A high pH is usually an indicator of urinary infection. PH contributes to the formation of bladder stones for example, struvite stones are normally formed is association with urinary infecions. Vegetarian diets and certain prescription foods also alter the pH of the urine e.g. Hills s/d® .

Cells

Red blood cells in the urine usually indicate cystitis but can be caused by bleeding disorders or tumours. Leucocytes (white blood cells) indicate infection in the urinary tract. The presence of cellular casts indicates inflammation and is significant. Bacteria should not be present, culture and sensitivity is recommended when bacteria have been detected.

Crystals

Crystals are the precursors to bladder stones which are also called uroliths or calculi. Common crystals are struvite (triple phosphate), calcium oxalate or urate, less common is cystine. Struvite stones are the most common and often are associated with concurrent bladder infection. Treatment is either diet to modify urinary pH and phosphate levels or surgery. Urate stones are seen in Dalmatians and dogs with porto-caval shunts.

Urinary infection

The following changes may be seen in a dog or cat with urinary infection:

  • Raised protein (most common)
  • Erythroctes (very common)
  • Leucocytes (less common)
  • Bacteria (less common)

Increased protein is the first sign of inflammation of the bladder, followed by bleeding. White blood cells in the urine are seen later in the response to the infection and bacteria are not always detected. Cats can have “sterile” cystitis.

ERD

Early renal detection test looks for the presence of tiny amounts of protein in the urine of dogs and cats, which is an early indicator for kidney disease. This test is the most accurate way to determine if a pet’s kidneys are normal. Other tests traditionally used do not indicate any dysfunction of the kidneys until 75% of the kidneys are damaged. Pets with moderately elevated albumin leakage from the kidneys should be evaluated for disease that can predispose the pet to kidney damage. These diseases are heartworms, dental disease, skin disease, chronic intestinal disease, or other chronic inflammatory conditions.

This test should be repeated in two months to see if the condition has resolved or is worsening. If these tests indicate a progression, additional tests such as an ultrasound and a kidney biopsy may be considered. Antioxidants are also recommended in some cases of chronic renal disease.

Did you know:

  • renal comes from the Latin word for kidney renes and nephron comes from the Greek word for kidney nephros?
  • The kidney filters 1 liter of blood a minute for an average male or 1,440 liters per day.
  • There are about 1 million nephrons in each kidney
  • The left kidney sits higher up than the right kidney and is slightly bigger.
  • The kidneys receive 20% of the total blood supply
  • We can live on one kidney