Urine Analysis - Pathology
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Introduction
Urine Analysis can be a quick and inexpensive method to determine abnormalities in a patient.
Techniques
Urine samples should be processed by noting their gross appearance, testing with a urinary dipstick, mesuring the specific gravity with a refractometer and by microscopic examination.
Gross Appearance
Specific Gravity
Urine specific gravity (USG) is measured using a refractometer calibrated for veterinary use. It must additionally be calibrated on each use using water which must match the water line on the refractometer read out prior to measuring USG, as reftractometer measurement is sensative to room temperature. Adjustments are made using the screw on the top of the refratcometer - take care not to get this screw wet when cleaning the reftractometer.
Specific gravity relates to the urine concentration. It is basically a measure of the density of particles in the urine.
Below are the normal urine specific gravities for the common domestic species.
Urinary Dipsticks
pH
In dogs and cats an acidc pH is normal. In the ruminants and horses the opposite is true and the urine is alkali. The pH does however vary with diet and medications as well as in pathological states so this needs to be accounted for. The normal range is 5-9
Protein
It is not common to find protein in the urine of normal animals. However it can be normal for small amounts to be found in the urine of dogs with a high specific gravity. Therefore this needs to be taken into account.
Glucose
The presence of glucose in the urine is termed glucosuria and occurs when the level of glucose reaches the renal threshold for glucose reabsorption. It is not normal to find glucose in the urine.
Ketones
It is not normal for ketones to be present in the urine and they are indicative of pathological states
Bilirubin and Urobilinogen
Small amounts of bilirubin can be found in dogs with concentrated urine therefore this needs to be interpreted in light of the urine specific gravity. However as a rule it is not normal to find bilirubin in urine.
Urobilinogen is formed from bilirubin in the intestine and small quantities are normally found in the urine.
Blood
The presence of blood in the urine is not normal and is usually related to a pathological state.
Microscopic Examination
Cellular Deposits
- Epithlial cells
- Renal
- Squamouns
- Transitional
- Leucocytes
- Red blood cells
- Intact
- Ghost
- Crenated
- Bacteria
- Other
- Fat droplets
- Yeast bodies
- Sperm
- Artefacts
Casts (Cylinduria)
- Hyaline
- Waxy
- Granular
- Cellular
- Fatty
- Haemoglobin
- Myoglobin
- Artefacts
- mucus threads
Crystalline and Amorphous Deposits
- Calcium carbonate
- Struvite
Calcium Oxalate
- Dihydrate
- Monohydrate
- Amorphous phosphate
- Leucine
- Tyrosine
- Cystine
- Amorphous urates
- Uric acid
- Sodium urate
- Dicalcium Phosphate
- Ammonium Biurate
Culture and Sensitivity
Free catch samples which are collected from naturally voided urine will inevitable be contaminated by the bacteria of the external genitalia and skin. Where culture is essential for diagnositc and treatment purposes, a sample obtained by cystocentesis or catheterisation will be required. Catheterisation carries the risk of introducing infection iatrogenically.
Culture on blood agar and CLED (with Andrades indicator - for E coli) plates will help with a speedy diagnosis of causal organisms.