Introduction to Urinalysis

Laboratory Procedures

Urinary System

Designed to maintain a balance between fluid, electrolytes, and acid-base homeostasis by selectively eliminating waste products from the body.

Urine is formed through glomerular filtration, tubular reabsorption, and tubular secretion (remember everything you were taught in A&P). These are influenced by hormones

Medical Terminology

Pollakiuria Frequent urination

Polyuria Increased urine output or production

Oliguria Decrease in the formation or elimination of urine

Anuria Complete absence of urine formation or elimination

Dysuria Difficult urination

Urinalysis

Urine collection can be accomplished through mid-stream free catch, manual expression, catheterization, and cystocentesis.

Advantages to Urinalysis

Fast Simple Inexpensive Provides useful information (urinary tract

and/or other body systems)

Voided Urine Sample

Easiest to obtain May be contaminated

from distal genital tract Not satisfactory if

examining for bacteria.

Voided Urine Sample Collection Use a clean container Wash prepuce or vulva (when possible) Try to collect mid-stream urine

Disadvantages to Voided Sample Contamination Difficult in cats May be difficult in easily scared dogs and

short breeds

Expressing the Bladder

Use steady gentle pressure Will feel like a balloon or ball under your hands. Make sure you are expressing in a squeezing

motion where you are forcing urine down urethra. Wash external genitalia Contamination from lower urinary tract/genital

tract is a concern. DO NOT DO MANUAL EXPRESSION

WHEN THERE IS AN URETHRAL OBSTRUCTION!!!

Urinary Catheterization

Act of placing a catheter through urethra into bladder

Advantages: Less possibility of contamination from lower

genital tract. Helpful in obese animals when bladder is difficult

to palpate Disadvantages

Trauma to sensitive urethral mucosa Possible contamination

Cystocentesis

Act of obtaining a urine sample via a needle and syringe directly from the bladder

Advantages Sterile sample

Disadvantages Difficult to obtain in obese animals Trauma to organs if not done correctly

Urine Sample Preservation

Analyze all urine within 30 minutes if possible

May refrigerate for 6-12 hours if needed Bring to room temperature

before anlaysis Morning samples are

more concentrated If allowed to stand at

room temperature, may get false results.

Physical Characteristics of Urine Color Transparency Odor Specific gravity Volume

Urine Color

Normal color is due to pigments called urochromes

Normal: light yellow to amber color Abnormals:

Red: blood (hematuria) Reddish-brown: Hemoglobin or Myoglobin Dark yellow-brown: Bilirubin (bilirubinuria) Orange-Reddish brown: Normal in rabbits

Urine Transparency

Clear vs. Cloudy Cloudy could indicate increase cells, mucus,

casts, crystals and bacteria. Horses and some rabbits have cloudy urine

due to high content of mucus and calcium carbonate crystals.

Urine Odor

Not Very diagnostic Strong odor may suggest bacterial production Male cats, goats, and pigs have a very strong

urine odor

Urine Specific Gravity

Measure urine concentration which is dependent on the number, molecular size, and weight of urine solutes

Measures the density of urine as it compares to water

Specific gravity of water is always 1.000

“Normal” Urine Specific Gravities Man: 1.003-1.037 Dog: 1.013-1.030 Cat: 1.013-1.050 Horse: 1.015-1.045

Methods of collecting a urine specific gravity Refractometer Reagent strip Urinometer

Causes of Altered Specific gravity Increased specific gravity

Dehydration Increase fluid loss Decreased water intake

Decreased specific gravity Kidney disease Excessive water Pyometra Some drugs

Urine Volume

Influenced by several factors Water intake Size of animal Species of animal

Crystals

The presence of crystals in the urine is called crystalluria.

There are many types of crystals that can form in urine, we are going to cover just a few. (More to come in Clinical Pathology!)

Crystalluria may or may not be of clinical significance. Certain crystals form as a result of elements being

secreted into the urine by normal renal activity.

Crystal formation

Crystal formation depends on the pH of the patients urine.

Some crystals form in acidic urine, while others form in basic or neutral urine.

If a urine sample is allowed to stand and cool to room temperature, the number of crystals in the urine will increase because the material that forms the crystals is less likely to dissolve at cooler temperatures.

Types of crystals

Triple phosphate Includes Struvite, and Ammonium Magnesium

Phosphate. While their name may be interchanged, these

crystals have slightly different composition. Generally appear as “coffin lids” or roof-tops Form in alkaline to slightly acidic urine.

May take a fern-leaf shape if urine has high concentration of ammonia

Calcium Oxalate Dihydrate

Generally appear as small squares with a visible “X” across the top of the crystal.

Most often form in acidic and neutral urine. Are commonly seen in small numbers in dogs

and horses. If seen in large numbers, can indicate calculi

formation.

Calcium Oxalate Monohydrate May be small and “dumbbell” shaped, can

also appear as a slat from a picket fence. Generally form in any pH urine, but are a key

indicator if an animal is experiencing ethylene glycol toxicity!

Uric Acid/Ammonium Urate Crystals Uric Acid crystals often appear as yellow-

brown “rosettes” or as diamond-shaped “plates”. Can form in any pH urine!

Ammonium Urates often appear as “thorn-apples” Generally form in neutral to alkaline urine.

Are very rarely seen in dogs and cats. (Except Dalmatians!!)

Uric Acid Crystals

Ammonium Urate Crystals