Urinalysis Flashcards
Why are urinalyses done? What are the main 3 indications?
evaluates what the kidney is excreting, which provides insight into renal function, metabolic disease, and systemic disease
- health screening
- pre-anesthetic assessment
- minumin database
How does the timing of the sample collection commonly affect urinalysis?
- early morning = more concentrated
- post-prandial = more alkaline
- after fluid or diuretic therapy = more dilute
What are the 3 options for urine collection from least to most invasive?
- voided sample (free catch)
- urinary catheterization
- cystocentesis
How are voided samples collected? What is is acceptible for? When should it not be used?
catch mid-stream flow
acceptable for urinalysis, but not suitable for cultures, since bacterial contamination is common
When is urethral catheterization suitable? What contamination is common?
acceptable for both urinalysis and culture
blood or epithelial cells
In what animals is urinary catheterization more difficult? In what condition is it done? What risk is taken?
females
sterile
bacterial introduction into the bladder
What is cystocentesis? What is it used for? What contamination is common?
sterile and ultrasound-guided procedure when a needle is passed directly into the bladder
acceptable for urinalysis, ideal for culture
blood
When is it ideal to analyze a urine sample? Why?
within 30 mins
- low USG may cause cellular lysis
- urine crystals may dissolve or develop
If urine samples cannot be observed within 30 minutes, what should be done? Once it is ready for observation, what needs to be done?
refrigerate in a sterile, opaque, airtight container for up to 12 hours
warm to room temperature and gently resuspend sediment prior to analysis
What is the first part of the complete urinalysis?
gross inspection - color and clarity
What are the 5 common colors of observed urine?
- pink-red = hematuria, hemoglobinuria, myoglobinuria
- red-brown = hematuria, hemoglobinuria, myoglobinuria
- brown-black = methemoglobinuria, bile
- yellow-orange = highly concentrated, bilirubinuria
- yellow-green = bilirubin, biliverdin
What are the 5 levels of clarity of urine samples? What affects this?
- clear
- slightly cloudy
- cloudy
- opaque
- flocculent
formed elements - crystals, cells, bacteria, lipids
What does the USG measure? Under what conditions should urine be observed? Why?
dissolved molecules —> solutes
room-temperature urine - cold fluids are more dense and will have falsely increased USG
How is the chemical evaluation of a urine sample done? What does it measure? What values are inaccurate in veterinary medicine?
dipstick - semiquantitative: negative, trace, 1+, 2+, 3+, 4+
glucose, bilirubin, ketones, heme, pH, protein
leukocytes, USG, nitrite, urobilinogen, ascorbic acid
How is glucose usually metabolized in the kidneys? When does glucosuria occur in dogs, cats, horses, and cattle?
small molecule that is freely filtered by the glomerulus and completely reabsorbed in the proximal tubules
when reabsorption capacity is exceeded…
- DOGS = 220 mg/dL
- CATS = 280 mg/dL
- HORSES = 180 mg/dL
- CATTLE = 100 mg/dL
What is the most common differential for glucosuria? What else can be considered?
hyperglycemic - diabetes mellitus, acute pancreatitis, stress (corticosteroids in cats), glucose-containing fluids
- normoglycemic - acute kidney injury, reversible tubular damage (drugs, toxins), urethral obstruction in cats
- Fanconi syndrome (Basenjis, Labs) - proximal tubular defect that causes impaired tubular reabsorption of glucose, amino acids, and phosphate, resulting in normoglycemic proteinuria and glucosuria
What is bilirubin? How does it move through the kidney? Does bilirubinemia or bilirubinuria occur first?
product of RBC Hgb degradation that is conjugated in the liver
unconjugated bilirubin circulates bound to albumin and cannot pass through the glomerulus; once it becomes conjugated, it can pass through and is not reabsorbed by the tubules
bilirubinuria —> low renal threshold
When is bilirubinuria normal in dogs? Is bilirubinuria normal in cats?
normal to see trace to 1+ in dogs with concentrated urine
NO - always considered abnormal
What 4 things does bilirubinuria possibly indicate? What toxicity can cause this? What is a common cause of false negatives?
- obstruction of bile flow and regurgitation of conjugated bilirubin in the blood
- increased tubular cell formation with hemoglobinuria
- increased hepatic conjugation with intravascular hemolysis
- IMHA
red maple leaf, onion, garlic, acetaminophen
delayed sample processing or excessive light exposure
What 3 ketones are seen in urine? When are they produced?
- β-hydroxybuterate
- acetoacetate*
- acetone*
when energy production shifts from carbohydrate to lipid metabolism
What ketone is most commonly found in ruminant urine?
β-hydroxybutyrate —> not detected on dipstick!
What are 4 possible causes of ketonuria?
- diabetic ketoacidosis (dogs and cats)*
- negative energy balance
- diabetes mellitus
- ketosis (cattle)
What is the most common cause of a positive heme/blood reading on the dipstick?
hematuria —> full RBC
What 3 conditions show a positive result on heme/blood on a dipstick?
- HEMATURIA - red, cloudy urine that clears after centrifugation (should see RBC pellet in
centrifuged tube and on sediment exam) - HEMOGLOBINURIA red urine that does not clear after centrifugation, lacking RBC pellet in centrifuged tube —> supernatant REMAINS red
- MYOGLOBINURIA - red-brown urine that does not clear after centrifugation —> supernatant REMAINS red
What is also seen with hemoglobinuria with intravascular hemolysis? What is myoglobinuria indicative of?
hemoglobinemia (red plasma) - look for anemia
muscle disease —> increased creatinine kinase and AST on biochem
What is the normal pH of dog and cat urine? What 3 things affect this?
5.0-7.5
- diet
- collection time - post-fasting vs. post-parandial
- systemic acid-base status
What are 6 causes of developing acidic urine?
- meat protein-based diet
- use of acidifying agents
- metabolic/respiratory acidosis
- paradoxical aciduria with metabolic alkalosis
- protein catabolic state
- ethylene glycol ingestion
What are 6 causes of developing alkaline urine?
- plant protein-based diet
- post-prandial alkaline tide
- UTI with urease containing bacteria that can produce ammonium
- urine sample exposed to air at room temperature
- use of alkalinizing agents
- metabolic and respiratory alkalosis
What protein does the dipstick detect? What are 3 common causes of false positives? 2 causes of false negatives?
negatively charged albumin
FALSE POSITIVES - alkaline urine, cauxin (albumin-like protein) naturally in cat urine, hypersthenuria
FALSE NEGATIVES - below 20-30 mg/dL lower limit, insensitive to globulins and Bence-Jones proteins
What are 3 common causes of proteinuria?
- positive protein reactions
- renal disease - negative blood reaction, measure UPCR
- glomerular disease - nothing in sediment
What 3 things must be ruled out to confirm positive protein reactions caused proteinuria? What is seen in each case?
- hemorrhage - positive blood reaction results in RBCs in sediment
- UTI/cystitis - bacteria and WBCs in sediment
- intravascular hemolysis - hemoglobinuria, anemia
How can dipstick protein results be confirmed? How is this done?
sulphosalicylic acid test (SSA) - reacts with albumin, globulins, and Bence-Jones proteins
add 5% sulphosalicylic acid to supernatant and compare the resulting turbidity to standards
(interpret dipstick with SSA, USG, chemistry panel, and presenting clinical signs!)
What is nephrotic syndrome? What are 4 characteristics?
rare complication of protein-losing nephropathy causing abdominal effusion/transudation
- proteinuria
- hypoalbuminemia
- peripheral edema or third spacing (ascites)
- hypercholesterolemia
What is Fanconi sydrome? What does this result in? In what species is it commonly hereditary? What causes acquired cases?
proximal tubular defect that causes impaired tubular reabsorption of glucose, amino acids, and phosphate —> proteinuria and glucosuria with normoglycemia
Basenjis (and Labs) - typically diagnosed by 3-4 y/o
chicken jerky treat recall, copper storage disease, heavy metal toxicity
What are the 6 steps to examining urine sediment microscopically?
- centrifuge at slow speed for 5 mins
- decant urine without disrupting sediment (leave a small amount of urine)
- re-suspend urine
- transfer a drop to a glass slide and place a coverslip
- lower condenser on a microscope
- examine edge of coverslip at 10x for epithelial cells and 40x for RBCs, WBCs, fat, and microorganisms
What are 4 common sources of epithelial cells in microscopic examination of urine sediment?
- SQUAMOUS CELLS - distal urethra, vaginal tract, skin
- TRANSITIONAL CELLS - renal pelvis, ureter, bladder, proximal urethra
- caudate cells - renal pelvis with pyelonephritis
- renal cells - tubules with injury
What is the structure of the squamous cells seen in urine sediment? What is their significance?
large, thin, transparent, angular or folded
common in free catch urine and rarely pathological, but may be increased with Sertoli cell tumors causing squamous cell metaplasia
What is the structure of transitional cells seen in urine sediment? What is their significance?
round, variable size, found individually and in clusters
- hyperplasia associated with inflammation
- transitional cell tumors
What is required to diagnose transitional cell carcinoma? Why?
clinical pathologist —> respond to inflammation with high variability in size and morphology, so it is easy to mistake inflammation for neoplasia
What samples should be sent to clinical pathologists for transitional cell carcinoma diagnosis? What is the best method of obtaining samples?
air-dried sediment or cytocentrifuged preparations
catheterization - unusual to see on cystocentesis
What is the structure of RBCs in urine sediment? What is their significance? Why should the method of sample acquirement be considered?
round, yellow-tinged, crenated
hemorrhage, inflammation
microscopic hematuria is expected on a cystocentesis sample
How do WBCs compare to RBCs on urine sediment samples? When is it considered pathological?
2x larger than RBCs with granular cytoplasm
< 5 WBCs/40x hpf = normal
> 5 WBCs/40x hpf = pyuria
What are 4 general causes of pyuria?
- UTI - pyelonephritis, lower UT (culture even if no bacteria are visible)
- non-infectious inflammation - cystitis from calculi
- neoplasia
- prostatitis
How many rods and cocci need to be present to observe in urine sediment? How are they reported? What else is expected in these samples?
> 10,000 rods/mL
100,000 cocci/mL
no standard - few to many, present vs. absent
NEUTROPHILS (unless immunosuppressed by steroid therapy, Cushing’s, diabetes, FIV, etc.)
What kind of cultures should be ran for UTIs?
- aerobic
- quantitative measurements
- sensitivity MIC
What should be considered if unusual infectious agents are observed in a urine sample?
- clinical signs
- method of collection: voided with possible fecal contamination
- sample storage: where, how long
- immunosuppressed patient
- other supportive diagnostic findings with infection
What in vivo and in vitro factors contribute to urine crystal formation?
IN VIVO - concentration and solubility of crystalline material, urine pH, diet, excretion of drugs or diagnostic imaging agents
IN VITRO - temperature decreased causing a decreased solubility, evaporation increases solute concentration, urine pH changes when left sanding due to bacterial overgrowth
What are the 5 most common crystals found in urine? What other ones are less common?
- amorphous
- bilirubin
- calcium carbonate
- calcium oxalate dihydrate
- struvite
ammonium bitrate, calcium oxalate monohydrate, cysteine, drug-associated
What is the typical appearance of amorphous crystals? What significance does it have?
yellow (brown) aggregates of finely granular material with no defining shape
NONE
What is the typical appearance of struvite crystals (triple phosphate, magnesium ammonium phosphate)? What species are they most commonly found? What promotes their formation?
large, colorless, prism-like crystals with a “coffin lid” shape
dogs and cats
formation is favored in neutral to alkaline pH and urease-positive bacteria will promote formation due to the increase in pH
What is the typical appearance of bilirubin crystals? In what species are they normal to find in the urine? When are they considered pathological?
orange to copper granules present in small bundles
DOGS - low numbers in highly concentrated urine
ALL OTHER SPECIES - icterus (pre-hepatic = hemolysis, hepatic/post-hepatic = heptobiliary disease)
What is the typical appearance of calcium carbonate crystals? What is their significance?
variably sized, colorless to yellow-brown spheres with radial striations
NORMAL in horses, rabbits, guinea pigs, and goats (not reported in canine or feline urine)
What is the typical appearance of calcium oxalate crystals? When are they normally seen? In what 3 situations are they considered pathological?
colorless squares connected by intersecting lines, giving it an “envelope” appearance
normal in domestic species and as storage artifacts
- Mini Schnauzers are predisposed
- hypercalcemia causing increased calcium excretion
- acute renal failure
What are urinary casts? When are they formed? What can they indicate?
Tamm-Horsfall protein - mucoprotein secreted by tubular epithelium of the loop of Henle, distal tubules, and collecting ducts
acid urine, also depending on solute concentration and flow rate (dissolved in alkaline urine)
tubular damage and/or urine stasis within tubules (increased = cylindruria)
What are the 4 types of urinary casts?
- hyaline - 10x objective, > 2 is significant
- cellular - epithelium, RBCs, WBCs
- granular
- waxy - chronic
Urinary casts:
In what species are fat droplets commonly found in urine? What causes their development? How can they be differentiated from RBCs and WBCs?
feline - very commonly insignificant in other species
degeneration of epithelial cells lining the urinary tract
found in a different plane of focus and are more uniformly round than cells
In what species is it common to find mucus in their urine? What do they look like?
horses
resemble hyaline casts, but are more irregularly shaped with tapered edges
What is the most common source of contaminant fibers in urine? What may they be confused with?
cotton, plants, and paper
mimics parasite larvae or urinary casts
Environmental fungi and pollen:
