Clin Path

Question 1

describe urinary function markers

Answer 1

1. urea nitrogen: labs may report as UN, BUN, or urea
   -made in the liver
   -urinary tract most important route of excretion
2. creatinine
3. SDMA

Question 2

what does an increased urea nitrogen indicate?

Answer 2

1. decreased urinary excretion
   -dehydration/hypovolemia
   -kidney dysfunction
   -outflow obstruction
2. increased protein digestion or catabolism
   -GI hemorrhage
   -high protein diets, starvation

Question 3

describe urea nitrogen as an indication of early kidney insufficiency

Answer 3

POOR indicator of early kidney insufficiency

-once majority compromise occurs, THEN UN increases above reference interval

-extrarenal factors: rumen recycling, horses lose through gut

Question 4

when does an increased creatinine occur?

Answer 4

1. decreased urine excretion
   -dehydration/hypovolemia
   -kidney dysfunction
   -outflow obstruction
2. very muscular animals

Question 5

describe creatinine as an indicator for early kidney disease

Answer 5

1. POORly sensitive for early kidney disease
   -once 75% compromise occurs, THEN creatinine increases above reference interval
2. BUT is better than urea nitrogen in ruminants and horses
   -not affected by rumen recycling or GI tract dumping

Question 6

describe SDMA

Answer 6

1. more sensitive reflection of GFR in dogs and cats
   -may increase before creatinine and UN with impaired kidney function
   -increased occur due to primary kidney disease as well as other conditions that affect kidneys (dehydration, hypertension)
2. follow up an increased SDMA with serial monitoring or further diagnostics like creatinine

Question 7

describe azotemia

Answer 7

1. increased non-protein nitrogenous compounds in the blood
   -increase in serum urea nitrogen and/or creatinine concentration and/or SDMA
   -reflective of GFR
2. use urine specific gravity to differentiate between prerenal, renal, and postrenal

Question 8

describe urine specific gravity

Answer 8

1. reflects tubular ability to concentrate or dilute
2. estimated by refractometry
   -change in light refraction is proportional to amount of solute
3. artifacts exist!
   -marked glucosuria or proteinuria

Question 9

describe hypersthenuria, isosthenuria, and hyposthenuria

Answer 9

hypersthenuria:
-highly/adequately concentrated urine
-USG cutoff is species dependent
–cats: greater than or equal to 1.035
–dogs: greater than or equal to 1.030
–horses and cattle: greater than or equal to 1.025
-although this is the goal, normal hydrated animals can intermittently not meet these criteria at random times (random one off not super concerning but if a trend = get concerned)

isosthenuria: urine osmolality = plasma osmolality
-tubules did not dilute or concentrate (kidney was dormant)
-USG 1.008-1.012

hyposthenuria: diluted urine
USG less than or equal to 1.007

Question 10

how are urine markers different in avians and reptiles?

Answer 10

1. creatinine and urea nitrogen are rarely helpful
2. uric acid is a major nitrgenous waste product in birds and terrestrial reptiles (uricotelic)
   -blood concentrations can be increased (hyperuricemia) due to impaired renal function, dehydration can also affect
   -not particularly sensitive, so requires more than 67-75% functional mass loss to see elevations in blood
3. USG also less useful due to inability to concentrate urine (reptiles), mixture with feces, wide normal ranges (birds), small sample volume, etc.

Question 11

describe prerenal azotemia causes (3)

Answer 11

1. reduced renal blood flow (due to hypovolemia from dehydration or shock)
2. decreased UN and creatinine clearance
   -USG values:
   -greater than or equal to 1.025 in horses and cattle, 1.030 in dogs, and 1.035 in cats
   -so will see increased UN and creatinine
3. increased urea production
   -upper GI hemorrhage: digested blood is source of urea
   -high protein diets
   -mildly increased UN and normal creatinine: urea production exceeds excretion
   -USG variable

Question 12

describe renal azotemia

Answer 12

1. any renal disease that decreases GFR below 25%
   -approx 75% loss of nephrons
2. USG:
   -1.008-1.012 (isosthenuria) but not always if kidneys can concentrate to some degree
   -but always less than the adequate cutoff for the species

Question 13

describe postrenal azotemia

Answer 13

1. excretion challenge such as urinary tract blockage or rupture
2. USG is variable: depends on hydration status and presence or absence of concurrent renal disease
3. hyperkalemia OFTEN present:
   -decreased potassium excretion through urinary tract causes hyperkalemia!!
   -hindered urination versus hindered urine production (both can cause postrenal azotemia)
   -no USG to help clue you in; urine was already concentrated or not before it reached post-renal so elevated potassium is most helpful indicator or urinary obstruction!!!

Question 14

what are other blood analytes affected by urinary disorders?

Answer 14

GFR:
-urea nitrogen
-creatinine
-SDMA

glomerular filtration barrier compromise:
-albumin and others!

tubular function alterations:
-sodium and chloride
-potassium
-bicarbonate
-calcium
-magnesium
-phosphorous
-albumin
-glucose
-others!

Question 15

describe the components of a UA

Answer 15

macroscopic:
1. color
-light yellow/straw: normal
-colorless: very dilute
-dark yellow to orange or yellow-green: bilirubin
-white: pyuria, crystalluria
-red to brown: RBCs, hemoglobin, myoglobin

2. clarity
   -normal is transparent
   -increased turbidity: increased cells, numerous crystals, bacteria, lipid, mucus, storage artifact
3. dipstick
   -pH: dogs and cats between 6-7.5, horses and cows 7.5-8.5
   -protein: 0-4+, normal is up to trace
   -glucose: 0-large, normal is none
   -blood/heme: 0-3+, normal is none
   -ketones: 0-large; normal is none
   -bilirubin: 0-3+, normal is up to 1+

-USG

microscopic: sediment examination

Question 16

what can affect urine pH?

Answer 16

1. kidney acid/base management
   -diet
   -systemic acid/base status
2. bacteria
3. age of specimen

aciduria:
-carnivores (protein breakdown)
-acidosis

alkalinuria:
-herbivores
-alkalosis
-urease-containing bacteria
-prolonged storage at room temp

Question 17

describe how to interpret urine protein (4)

Answer 17

1. normal urine contains little to no protein
2. dipstick primarily measures albumin
   -NOT globulins (all other large proteins) so is a limiting factor
3. false positive proteinuria on the dipstick is common (dipstick is a hypochondriac)
   -alkaline urine (normal for herbivores)
   -increased contact time with dipstick
4. consider USG before reacting!!
   -if only 1+ and concentrated urine is not as concerning as dilute urine bc the other factors concentrating can increase protein excretion but at least you’re concentrating

Question 18

describe prerenal, renal, and postrenal causes of proteinuria

Answer 18

prerenal: larger quantity than normal of relatively small proteins
1. colostrum-drinking baby
2. Hbg, Mgb, Bence-Jones proteinuria
-bence-jones proteins lumped with cancerous or neoplastic disorders

renal:
1. glomerular disease
2. tubular disease

postrenal:
1. hemorrhage
2. inflammation

Question 19

describe urine blood (heme) on a dipstick

Answer 19

positive dipstick result may com from:
1. hematuria (intact RBCs)
-after centrifugation: RBCs found in sediment, but urine supernatant is clear
-clear plasma
-this tells does NOT tell us the source of the RBCs, we just know that they’re causing a positive heme

2. hemoglobinuria or myoglobinuria
   -after centrifugation: red/brown color persists throughout
   -red or pink plasma (if hemoglobin): signs of hemolytic anemia?
   -clear plasma (if myoglobin): signs of muscle damage?
   -if muscle damage, may also see elevated CK and AST

urine blood (heme) will cause urine protein to also be positive once urine is visibly pink to red

Question 20

describe urine glucose on a dipstick

Answer 20

1. urine does NOT normally contain glucose
2. when present, urine reflects glucose status over the past few hours (or since animal emptied its bladder)
3. renal threshold for glucose: blood glucose value that exceeds the maximum tubular resorption capacity
   -cattle: 140mg/dl
   -horses: 180mg/dl
   -dogs: 180 mg/dl
   -cats: 280 mg/dl

Question 21

describe how to interpret urine glucose

Answer 21

1. glucosuria with persistent hyperglycemia: suspect diabetes mellitus
2. glucosuria with transient hyperglycemia: any cause that exceeded renal threshold
3. glucosuria with normoglycemiaL suspect renal tubular problem

challenging to differentiate with single sample if blood glucose has already returned to WNL

Question 22

describe urine ketones on a dipstick

Answer 22

ketosis is due to negative energy balance

4 causes:
1. diabetes mellitus/diabetic ketoacidosis
2. bovine ketosis
3. late pregnancy/early lactation
4. starvation

Question 23

describe bilirubin on a dipstick

Answer 23

1. bilirubin comes from breakdown of RBCs
2. mild (up to 1+): common in dogs, especially in males
3. or due to hepatobiliary disease or hemolysis

Question 24

describe the typical urine sediment in a healthy animal

Answer 24

1. squamous and transitional epithelial cells: varied in health
2. hyaline and granular casts: absent to very low numbers
3. crystals: absent to low numbers
4. RBCs: less than 5 per 40x field
5. WBCs: less than 5 per 40x field
6. no bacteria or other infectious organisms

Question 25

what do you look at in a urine sediment on the low power 10x objective

Answer 25

1. epithelial cells 2. casts 3. crystals

Question 26

describe squamous epithelial cells

Answer 26

1. contamination: urethra, vagina, or skin 2. most common in catheterized and voided samples 3. look like cornflakes!

Question 27

describe transitional epithelial cells

Answer 27

1. low numbers can be normal 2. catheterization, UTIs, neoplasia 3. look like/also called round epithelial cells -with a round distinct nucleus

Question 28

describe the types of casts seen

Answer 28

1. form in renal tubules 2. a few hyaline or granular casts can be found in healthy animals 3. casts deteriorate in urine quickly! if storing and then mailing out next day or over the weekend, may disintegrate by the time they reach the lab 4. presence in large numbers can indicate tubular disease 5. any cellular cast is indicative of a tubular problem -RBC or epithelial 6. fatty casts also abnormal

Question 29

what are the 6 common urine cystals?

Answer 29

1. struvite: magnesium ammonium phosphate -shaped like gold bars or and envelope! -can be found in healthy and unhealthy dogs and cats 2. calcium carbonate -common finding in NORMAL horses and rabbits -identified as spheres with radiating lines (when looking end on), ovals, and/or dog bone shapes -indicative of excessive calcium in the urine if found in other species 3. ammonium biurate -thorn apple shaped -often associated with liver disease (shunts) -can be normal in dalmations and english bulldogs 4. bilirubin -gold needles -seen with bilirubinuria, particularly with highly concentrated dog urine 5. calcium oxalate dihydrate -can see low numbers in health, but can indicate increased calcium and/or oxalates -square or cube with X in the center!! distinguish from struvite (which has no X) -can be associated with stone formation 6. calcium oxalate monohydrate -fence pickets, relatively flat -associated with ethylene glycol toxicity (early, before anuric phase)

Question 30

what do you look for in a urine sediment on high power 40x objective?

Answer 30

1. RBC 2. WBC 3. bacteria urine sediment is a wet mount prep (drop with a cover slip on top; cover slip is what makes 40x view clear!

Question 31

describe erythrocytes in a urine sediment (5)

Answer 31

1. smaller than WBCs 2. smooth texture 3. +/- crenation or central pallor (dogs) 4. greater than 5 RBCs per 40x field = hematuria 5. lipid droplets are around the same size, and lots in cats! must distinguish! -not crenated, no central pallor -when make wet mount, if let sit for just a few sec, fat will float up to the top of the urine and will put it out of the plane of focus of everything else

Question 32

describe leukcocytes in a urine sediment

Answer 32

1. larger than RBCs 2. granular/look like they're wearing glitter :) 3. greater then 5 WBC per 40x field = pyuria

Question 33

describe microorganisms in a urine sediment

Answer 33

1. include bacteria, fungi, yeasts 2. infection versus contamination -consider collection technique, presence of clinical signs, if inflammation is present, if patient is immunosuppressed (might see systemic fungal disease) 3. bacteria may still be present even if we don't see them! -a certain number must be present in order for us to recognize that it's there so 4. best follow-up testing for bacteria includes a urine culture; may consider an in-clinic option for further assessment

Question 34

describe the Idexx sedivue

Answer 34

1. automated urine sediment analyzer; takes approx 70 images 2. identifies a variety of urine elements (with limitations) 3. will flag items for review

Question 35

describe the urine protein: urine creatinine ratio

Answer 35

1. follow-up test used to further assess degree of proteinuria and true versus false positives on urine dipstick 2. usually greater than or equal to 1+ proteinuria needs confirmation 3. protein loss best determined by 24 hour excretion study, which is technically challenging 4. UPC ratio clinically useful substitute -creatinine clearance relatively constant -comparing urinary protein loss to creatinine excretion should reflect true changes in protein loss

Question 36

describe how to interpret the UPC ratio

Answer 36

1. dogs: -0.2-0.5 (borderline) -greater than or equal to 0.5 = overt proteinuria 2. cats: -0.2-0.4 (borderline) -greater than or equal to 0.4 = overt proteinuria 3. can also be used in horses 4. UPCs >2.0 suggestive of glomerular disease

Question 37

what are lab findings associated with dehydration? (5)

Answer 37

1. pre-renal azotemia 2. erythrocytosis 3. increased albumin: the body almost NEVER produces extra albumin so if see increased is a 99.99% chance that patient is dehydrated 4. increased globulins 5. increased sodium 6. increased chloride

Question 38

describe titrational metabolic acidosis

Answer 38

1. kidney controls the metabolic component of acid/base status by regulating bicarbonate 2. if bicarb if decreased in the blood = metabolic acidosis 3. 2 types of metabolic acidosis, but titrational metabolic acidosis is linked to urinary tract disease 4. titrational metabolic acidosis: low bicarbonate, high anion gap -differentials: KULE 1. ketones (ketosis, diabetic ketoacidosis) 2. uremic acid buildup (renal failure, uroabdomen, UT obstruction) 3. lactate excess (shock, grain overload) 4. ethylene glycol and its metabolites (toxnis)