12b. Urinalysis: Chemical Evaluation Flashcards
How do we chemically examine urine?
eval is semi-quantitative when using reagent strips
strips have pads that are impregnated w/ chemicals - when urine is applied, color changes
Must adhere to expiry date of urine strips to avoid falst neg results
keep lid of container tightly sealed to prevent color changes due to enviro conditions - don’t tough pads with your fingers!
How should we use chemical strips?
must be stored at room temp
should be fully immersed (dipped) in the urine w/ excess being wicked away by tilting the long edge on a paper towel (can pipette sample on test strip but must make sure pads are fully saturated)
Strips can be for individual tests or for multiple tests
must read color change @ appropriate times
Which chemical strips test results have limited reliability?
leukocyte tests - verify on microscopic exam
specific gravity
urobilinogen
nitrates
How do we test for pH of urine?
must be fresh and at room temp for testing - pH tends to inc the longer the sample is sitting at room temp
Can be measures w/ dipstick or a pH meter - meter more accurate, however strip gives sufficient results
<7 is acidic, >7 is alkaline
What might influence pH?
depends on animals diet
Forage based = alkaline urine
High protein, cereal based = acidic
meast based = acidic urine
What is the normal pH of dogs and cats in health? What about herbivores?
Have normal pH of 6-7. pH of dog and cat urine tends to inc shortly after eating due to alkaline tide
herbivores have alkaline urine in health
Why is pH useful for sediments?
will help identify structures present in urine sediment
struvite crystals tend to form in alkaline urine
calcium oxalate, cysteine and uric acid calculi tend to form in acidic urine
How can we utilize the fact that diet affects pH?
prescription urinary diets to prevent the recurrence of stones and crystals by acidifying the urine
they work by having inc salt content to inc drinking and diluting urine
also minimize pH fluctuations during alkaline tide
What can cause an increase in urine pH?
urease-prod bacteria to become more alkaline - possible w/ bladder infection or if urine is sitting for extended periods at room temperature
Stress and excitement can cause an inc in urine pH
alkalosis
urine retention, and medications
What might reduce the pH of urine?
a fever, starvation, acidosis, excessive exercise, and medications
What is proteinuria
its an abnormal increase in quantity of protein in the urine
D/C normally have 0 to trace amounts of protein in urine, why might the collection method affect this?
The bladder is highly vascularized, so if you poke it multiple times, you may pierce the vessels and blood has protein in it so artificially rise the amount
How should the presence of proteinuria be interpreted?
Based on quantification, urine collection method, microscopic exam of urine and USG - dilute urine can give false neg results
What might cause proteinuria?
urinary tract hemorrhage or inflam, renal tubular degeneration, exercise, fever, or due to contaminants from the genital tract, trauma from urinary catheterization, manual expression or cystocentesis
What might cause palse positive protein tests?
the result of extremely alkaline urine samples
What might the presence of cells and cats in the urine cause?
elevated protein lvls - supernatant should be retested
What does a urine dipstick test primarily test for?
albumin, less sensitive to globulins
the test strip should never be allowed to sit in sample, as there will be falst positives due to bleeding of buffers from one test pad to the other
What is the urine protein/creatinine ratio?
used to confirm whether the amount of protein present in the urine is significant or not
it eliminates the urine volume and USG as variables
can be done in house with some analyzers or as a referred out test
VERY COMMON, need to know!
What is glucosuria/glycosuria
presence of glucose in the urine
most commonly occurs when animal’s blood glucose conc exceeds the max renal tubular threshold
glucose should be evaluated along with blood glucose lvls
inc lvls of glucose or protein will inc USG
What might cause glucosuria?
diabetis mellitus
stress - possible in cats, uncommon
Postprandial effect after a high carb meal - uncommon
after receiving dextrose containing fluids
after a GA - rare
rarely w/ other dz conditions
What is ketonuria?
presence of ketones in the urine
The strips are only a screening test as certain ketone are not detected by stripes
DO detect acetoacetic acid and acetone
DO NOT detect b-hydroxybutyric acid
If there are insufficient carbs available to aid in metabolizing fatty acids, what happens to the urine?
Ketones will begin to appear
What might happen when carb metabolism is altered?
will cause body to shift to fat breakdown as source of energy > insufficient carbs available to aid in metabolising the fatty acids and ketones will appear
What are some causes of ketonuria?
diabetic ketoacidosis (DKA)
pregnancy toxemia in ewes, ketosis in lactating dairy cows, starvation, anorexia, low carb and high fat diet, liver dz
In which species is low lvls of ketones normal?
ruminants and rabbits
What will bacterial contamination do to ketome lvls?
will decrease ketone lvl so proper handling and storage are important
What are bile pigments?
include bilirubin and urobilinogen
Small amounts are normal in cattle + male dogs
rarely found in pigs, sheep, horses or cats - any amounts in cats is considered abnormal - usually due to liver dz, diabetes, aspirin toxicity, FIP, FIV or FeLV
What is is bilirubin int he urine called?
bilirubinuria
What causes bile pigments?
uruin generally dark yellow color
causes hemolytic anemia (most common in dogs), toxicities, liver dz or bile duct obstruction, obstructions of upper int tract
generally detected before jaundice is seen in patient
What are the testing conditions for bile pigments?
Fresh sample that is kept out of light and has not be refrigerated bc bilirubin is sensitive to both light and temperature
conc samples can give false positive
yellow, yellow-green, or brown foam on top of urine sample when shaken indicate high bilirubin, urobilinogen or protein lvls
What is urobilinogen?
normal in urine
screening test are considered questionable
urobilinogen very unstable
urobilinogen is a bilirubin derivative formed in the large intestine
What does hematuria, hemoglobinuria and myoglobinuria mean?
hematuria - presence of intact RBC’s in urine
Hemoglobinuria is presence of free hemoglobin in the urin
myoglobinuria is myoglobin in urine
Tests detects erythrocytes, hemoglobin or myoglobin
Describe the characteristics of hematuria
intact RBCs present due to hemorrhage somewhere in urogenitcal tract
gives the urine a cloudy, reddish color - red pellet after urine is spun down
when there are small amounts of blood that do not impart a color change, it is referred to as occult blood - will be picked up by chemical analysis and sediment exam
What are some causes of hemoglobinuria?
intravascular hemolysis - IMHA, neonatal isoerythrolysis, incompatible blood transfusions
certain heavy metals (copper), severe phypophosphatemia, postparturient hemoglobinemia in cattle, infections, toxins, hemolysis when cattle drink excessive amounts of water
How do we know if RBCs are present in the urine?
in very dilute or very alkaline urine, cells will lyse and ghost cells may be present
presence of hemoglobin in urine give sit a clear red to red-brown color - after centrifuging the urine will remain in red in color, no pellet it formed
confirm on micro exam, w/ hx, PE findings and additional lab procedures
What are the characteristics of myglobinuria?
myoglobin is a protein found in muscle tissue
caused by extreme muscle damage - will have inc in serum lvls of CK, LDH, AST (muscle derived enzymes), seen in exterional rhabdomyolysis
gives urine a dark brown to almost black appearance - in low conc it may look similar to hemoglobinuria - hx and clin findings to differentiate
How is leukocytes in the urine tested?
test strips give lg number of false negs
test considered unreliable and is often ignored
presence of absence of leukocytes must be confirmed microscopically
What might nitrates in the urine indicate? What is it useful for?
a pos test is significant as you do not get false negs
in lg anims, a pos result = UTI
in sm anims, generally only useful in rabbits
What is common with urinalysis analyzers?
in-clinic machines generally semi-automated.
machines will read the urine strips
separate machines now also available that will perform a sediment exam on the urine
reference labs may have automated machines that perform he chemical, physical and sediment analysis
