Lecture 11 9/24/24 Flashcards
What are the four factors that affect urine composition?
-quantity and composition of plasma
-glomerular filtration
-tubular function
-method of urine collection/sampling conditions/sample handling
What are the four components of a urinalysis?
-physical inspection
-USG
-biochemical analysis/dipstick
-microscopic sediment exam
What are the three urine collection methods?
-cystocentesis
-urinary catheter
-free catch
What steps should be taken during sample handling to avoid pre-analytical error?
-use clean sample container
-refrigerate if analysis cannot occur within 30-60 minutes
-try to get a mid-stream sample that is not contaminated with bacteria, dirt, or chemicals
What are the potential sample storage artifacts?
-bacteria multiply
-pH can increase
-cells and casts can degrade
-crystals may form
What are the normal findings on physical inspection?
-yellow color
-clear clarity
-ammonia-like odor
What type of sample is wanted for the urine dipstick test?
well-mixed aliquot of urine (uncentrifuged)
Which dipstick pads are not typically considered in a urinalysis and why?
-leukocytes: better information from sediment
-nitrite: not diagnostically useful
-urobilinogen: not diagnostically useful
-USG: better information from refractometer
What should be avoided when running a dipstick?
-reading pads at wrong time point
-letting urine from one pad run onto another
-using outdated dipsticks
-storing dipsticks improperly/with lid off
What are the characteristics of HGB and bilirubin in the urine?
-discolor urine, making pads harder to read
-can be interferents in urine testing
When should a dipstick control solution be used?
-opening a new shipment or lot number
-worried about dipstick integrity
-result make no sense and technique had no obvious errors
What can cause a falsely low pH on dipstick?
contamination with urine from neighboring protein pad
What can cause a falsely high pH on dipstick?
-prolonged sample storage
-contamination with detergent/disinfectant
What can cause a falsely high heme on dipstick?
hydrogen peroxide or bleach contamination
What can cause a falsely low bilirubin on dipstick?
-prolonged sample storage
-exposure of sample to sunlight
What can cause a falsely low glucose on dipstick?
-cold sample
-marked ketonuria or bilirubinuria
What can cause a falsely high glucose on dipstick?
hydrogen peroxide or bleach contamination
What are the characteristics of glucose on dipstick?
-negative in health
-freely filtered, then reabsorbed
-glucosuria seen when resorption mechanism is overwhelmed or there is tubular damage/defect
What are the differential diagnoses for glucosuria?
associated with hyperglycemia:
-stress
-dextrose admin.
-diabetes mellitus
associated with euglycemia:
-renal tubular dysfunction/damage
What is the consequence of prolonged glucosuria?
osmotic diuresis; primary PU, secondary PD, and low USG
What are the characteristics of bilirubin on dipstick?
-negative in health
-conjugated bilirubin is detected
-dogs may have mild positive if urine is concentrated
-positive result expected if patient has hyperbilirubinemia
What are the characteristics of ketones on dipstick?
-negative in health
-shift from using carbs for energy to fats results in ketonemia and ketonuria
-detects acetone and acetoacetate; not beta-hydroxybutyrate
What are the differential diagnoses for ketonuria?
-untreated/poorly controlled diabetes mellitus
-negative energy balance
What are the characteristics of hemoglobinuria?
-red urine appearance
-urine remains red upon centrifugation
-serum/plasma appearance is pink or red
-patient may also have hyperbilirubinemia, bilirubinuria, and/or anemia
What are the characteristics of myoglobinuria?
-red urine appearance
-urine remains red upon centrifugation
-serum/plasma appearance is clear
-patient may also have increased CK on chem.
What are the characteristics of hematuria?
-red, cloudy urine appearance
-red button forms and supernatant is clear upon centrifugation
-serum/plasma appearance is clear
-patient may have RBCs in sediment
What are the characteristics of pH on dipstick?
-carnivores typically have more acidic pH
-result is a crude estimate that may be an overestimate
-crucial measurements should be done with a pH meter
What are the characteristics of protein on dipstick?
-predominantly detects albumin
-positive result expected in samples with an “active” sediment (hematuria and/or pyuria)
-critical evaluation should be done with quantitative measurement
What are the characteristics of urine protein-to-creatinine ratio?
-done on chem. analyzer
-test urine with “inactive” sediment only
-creatinine filtration is relatively constant and therefore a good reference for protein
When is a urine protein-to-creatinine ratio indicated?
-done to evaluate and quantify pathological renal proteinuria
-most commonly done when patients have or are suspected to have CKD
What are the characteristics of UP:C interpretation?
-considered persistent proteinuria if documented in 3+ urine samples obtained 2+ weeks apart
-ratio greater than 2 in dogs or 1 in cats indicates glomerular disease
-increased ratio is associated with poor prognosis in animals with AKI/CKD
What are the steps of a urine sediment exam?
-use fresh specimen
-centrifuge
-decant majority of supernatant
-re-suspend button in small amount of supernatant
-place on slide with coverslip
-evaluate on 10x for casts
-evaluate on 40x for cells, crystals, and microorganisms
What are the different cast types made of?
-cellular: intact cells
-granular: partially disintegrated cells
-waxy: totally disintegrated cells
-hyaline: tamm-horsfall mucoprotein
What do hyaline and granular casts suggest?
-hyaline: glomerular proteinuria
-granular: renal tubular disease/damage
What are the characteristics of RBC and WBC presence on sediment?
-can be collection artifact
-0-5 cells per field on a 40x objective is normal
-TNTC if there are many cells
-increased RBCs is hematuria
-increased WBCs is pyuria
What are the characteristics of epithelial cells on sediment?
-can be collection artifact
-low #s of transitional and squamous cells expected
-increased transitional cells with abnormal morphology may indicate carcinoma
What are the characteristics of crystals on sediment?
-significance depends on # and type seen
-may or may not be associated with urolithiasis
-definitive analysis only done in specialized labs
What are the characteristics of bacteria on sediment?
-may be collection artifact
-may indicate UTI
-can have UTI in the absence of bacteria
-other microbes such as fungi and parasites are rare
What are the characteristics of struvite crystals?
-normal and common in dogs and cats
-especially occur in alkalinuria
What are the characteristics of calcium oxalate dihydrate crystals?
-normal and common
-can be seen in disease
What are the characteristics of calcium oxalate monohydrate crystals?
indicate ethylene glycol toxicity
What are the characteristics of calcium carbonate crystals?
normal in herbivores, especially horses
What are the characteristics of ammonium biurate crystals?
-rarely seen in health
-common in Dalmatians and english bulldogs
-typically associated with portosystemic shunt in other dogs and cats
