Clinical Pathology of the Urinary System Flashcards Preview

Semester II Pathology > Clinical Pathology of the Urinary System > Flashcards

Flashcards in Clinical Pathology of the Urinary System Deck (40):
1

RENAL FUNCTION

URINE PRODUCTION- to regulate body water, eliminate waste, maintain normal blood Na, Ca, K and P concentrations, and maintain pH.

ENDOCRINE FUNCTION- erythropoetin, vitamin D, renin.

2

URINE PRODUCTION

30% of the plasma that reaches the kidney gets filtered at the GLOMERULUS- forms ultrafiltrate.
-PCT- REABSORPTION of protein (nutrients)
-DESCENDING arm of Loop of Henle- WATER REABSORPTION.
-ASCENDING arm of Loop- ION REABSORPTION.
-DCT- HORMONE (aldosterone, PTH) MEDIATED reabsorption.
-Collecting duct- hormone mediated water reabsorption, acid base balancing, and collection of urine

3

PRODUCING CONCENTRATED URINE

Requires:
1. Appropriate concentration gradient
2. Antidiuretic hormone (ADH)
3. Kidney must respond to signal (hormones etc)

ie. the kidney must be functioning in order for concentrated urine to be produced.
Excess water intake -> dilute urine production
Insufficient water intake -> concentrated urine production.

4

ASSESSMENT OF URINE PRODUCTION

Refractometer used to measure urine specific gravity (USG)- read right hand side!
USG is a ratio of solution's (urine) weight:weight of an equal volume of water.
Refractometry is indirect measurement of USG
Change in light refraction is proportional to concentration of solute.
Artefacts- glucosuria (glucose in urine) and proteinuria can falsely elevate USG.
Some scales are temperature compensated, others must be adjusted depending on room temperatures.

5

HYPOSTHENURIA

Diluted urine.
Urine osmolality is LESS than isosthenuric values.
<1.007

6

ISOSTHENURIA

Urine osmolality is EQUAL TO plasma osmolality.
Non-functioning kidney.
1.007- 1.012

7

HYPERSTHENURIA

Concentrated urine.
Urine osmolality is high; the kidney is actively concentrating urine.
Rarely used term.

8

DIABETES INSIPIDUS

Lack of ADH OR kidney is not responding to normal ADH.

9

GLOMERULAR FILTRATION RATE

BEST PREDICTOR OF RENAL FUNCTION.
Rate at which fluid move through glomerular filtration barrier from plasma to glomerular filtrate.
Measured by determining the rate at which a substance that is not excreted or reabsorbed is cleared from plasma- expensive and difficult.
An estimate is used in practice.
UN and creatinine can be used in practice to estimate GFR.

10

CREATININE

Used to estimate GFR.
A byproduct of muscle metabolism.
Muscle mass and therefore production rate are relatively constant.
Freely filtered by glomerulus and not reabsorbed by renal tubules.
AN INCREASE IN CREATININE CONCENTRATION REQUIRES 75% LOSS IN FUNCTIONING NEPHRONS.
Specific, especially in ruminants and horses (where non-renal factors are not as significant)- creatinine is used for GFR instead of urea in ruminants, as urea is excreted in to the rumen so blood levels are relatively constant.

11

INCREASED CREATININE

Due to decreased urinary excretion eg. in dehydration, hypovolaemia, kidney dysfunction, obstruction of outflow.
High muscle mass- elevated creatine can be seen normally in certain breeds (greyhound)

12

DECREASED CREATININE

Rare, but can be seen in animals with low muscle mass/cachexia.

13

UREA (UN)

Used to estimate GFR.
Synthesised from protein breakdown in the liver.
Excreted by kidneys.
RUMINANTS- Urea is excreted in to the rumen to be used for amino acid synthesis by urease bacteria. Therefore, creatinine should be used to estimate GFR in ruminants.

14

INCREASED UREA

Due to decreased urinary excretion- dehydration, hypovolaemia, kidney dysfunction, outflow obstruction.
Increased protein catabolism or digestion will also increased urea- eg. GI haemorrhage, high protein diets, starvation.

15

DECREASED UREA

Liver insufficiency, low protein diets, urea cycle problems.

16

AZOTAEMIA

Increased non-protein nitrogenous compounds in the blood (creatinine and/or nitrogen)
Can be PRE-RENAL, RENAL or POST-RENAL. USG is required to differentiate between these types.
Types can occur alone or in combination.

17

URAEMIA

CLINICAL SIGNS reflecting renal failure- vomiting, diarrhoea, coma, ulcers, ammoniac breath.

18

PRE-RENAL AZOTAEMIA

-Reduced renal blood flow eg. dehydration, hypovolaemia.
-> decreased GFR
-> concentrated urine production- the kidney is actively concentrating to preserve water.
-> USG increased- >1.025 (cattle/horses), >1.030 (dogs) >1.035 cats -hypersthenuria.

-Increased urea production- high protein diet, GI haemorrhage etc. Creatinine is less affected.

19

RENAL AZOTAEMIA

Any renal disease that causes a major decrease in GFR.
Caused BY THE KIDNEYS.
75% non functioning nephrons are needed to see increased creatinine/UN and renal azotaemia.
USG is usually 1.007-1.012- ISOSTHENURIC

20

POST-RENAL AZOTAEMIA

Azotaemia caused after urine has been formed by the kindeys.
USG is variable.
Caused by urinary tract blockage or urine leakage.

21

FUNCTIONAL RENAL MASS

Two-thirds of functional renal mass can be lost before urine concentrating ability diminishes and isosthenuria is seen.

Three-quarters (75%) of functional renal mass must be lost before increased creatinine/UN- azotaemia- are seen.

22

OTHER LAB ABNORMALITIES IN AZOTAEMIC PATIENTS

-Total calcium- variable, usually low in dogs/cats/cattle with chronic renal disease (decreased Ca reabsorption due to decreased vitamin D production by kidneys).
HORSES excrete much Ca through the kidneys (and have a different active form of vitamin D), so calcium carbonate crystals in the urine and hypercalcaemia are normal.

-Phosphorous- Decreased renal clearance in dogs/cats leads to increased blood phosphorous (hyperphosphataemia). Cattle/horses show extrarenal excretion of phosphorous (GI tract), so may not show hyperphosphataemia.

-Potassium- Kidneys are main route of K excretion from the body, so anuric/oliguric (no/low urine) kidney disease will cause hyperkalaemia.
Cattle are more likely to have hypokalaemia.

23

SECONDARY RENAL HYPERPARATHYROIDISM

Hyperphosphataemia and hypocalcaemia in renal failure causes PTH stimulation.
-> INCREASED PHOSPHATURIA (phosphate in urine)
-> INCREASED Ca REABSORPTION by kidney, bone.

Parathyroid hyperplasia may develop.
Consequences- Tissue mineralisation (due to high phosphorous), fibrous osteodystrophy ('rubber jaw')

24

ACUTE RENAL FAILURE

-Reversible or irreversible- the magnitude of the azotaemia does not differentiate between these.
-Isosthenuria (urine is more concentrated if it was formed before the insult that lead to failure)
-Anuria- no urine, or oliguria- little urine. Leads to hyperkalaemia.

eg. Ethylene glycol poisoning- causes vomiting, ataxia, CNS depression. Can be detected early on with UV fluorescence (look for staining round mouth of animal).
Metabolism of ethylene glycol produces CALCIUM OXALATE MONOHYDRATE crystals 3 hours/6 hours post exposure in the cat/dog.
Causes titrational metabolic acidosis with increased anion gap, hypocalcaemia (Ca is precipitated in to crystals), hyperphosphataemia (some antifrezes contain phosphorous)

25

CHRONIC RENAL FAILURE

Not always able to determine acute or chronic based on laboratory date- consider duration of clinical signs.
-Chronic renal failure causes isosthenuria and azotaemia.
-Non-regenerative anaemia (decreased EPO production)
-Hypocalcaemia due to decreased active vitamin D production (not seen in horses- different active form)

26

URINALYSIS

WHENEVER KIDNEY FUNCTION IS BEING ASSESSED, URINALYSIS- USG + DIPSTICK (minimum)- SHOULD BE UNDERTAKEN.

-Physical examination- colour, clarity
-USG- using refractometer
-Chemical examination- dipstick
-Sediment examination- centrifuge and microscopy.

27

METHODS OF SAMPLE COLLECTION

-Cystocentesis- preferred method in dogs and cats, assesses pure urine before it passes through the lower urinary tract and becomes contaminated. Controversial in animals with bladder masses (TCC)- may contribute to tumour spread.

-Catheterisation- can be technically difficult in females, see contamination with erythrocytes, epithelial cells, external contaminants if inappropriate technique is used.

-Voided sample- midstream free catch is best, potential for contamination from skin, urethra and reproductive tract.

Whichever method is used, the lab should be told on submission of the sample.

28

CHEMICAL EVALUATION- URINE pH

ACIDURIA- normal to an extent in carnivores
-Metabolic or respiratory acidosis
-Paradoxical aciduria

ALKALURIA- herbivores naturally have more alkali urine.
-Urease-containing bacteria
-Prolonged storage at room temperature
-Metabolic/respiratory alkalosis.

29

URINE PROTEIN

A small quantity of albumin is filtered from the plasma and reabsorbed by tubules. Normal urine contains little to no protein.
-Always interpret urine protein in light of USG- trace protein in very concentrated vs very dilute urine.
-Dipstick primarily measures albumin
-Many false positives can occur eg. alkaline urine, increased contact time.

30

URINE PROTEIN:CREATININE RATIO

aka. UPC ratio.
A more accurate measurement of urine protein, as it negate the dilution or concentration of urine.
NORMAL- 1

A UPC ratio of >5 is indicative of a glomerular component.
Consider sediment contents before interpreation- active sediment eg. haemorrhage, inflammation, makes UPC ratio unreliable.

31

SOME CAUSES OF PROTEINURIA

PRERENAL- Fever, strenuous exercise, colostrum, haemoglobinuria, methaemoglobinuria, Bence-Jones proteinuria.
Too much protein is being produced.

RENAL- glomerular or tubular disease- problems with the glomerular filtration barrier or tubular reabsorption means that urine is 'escaping' in to the urine.

POSTRENAL- haemorrhage, inflammation (unless it occurs in the kidney- renal).

Method of urine collection is important- external contamination with proteins can occur with free catch/catheterisation.

32

URINE BLOOD

Haematuria- intact erythrocytes in urine. RED COLOUR CLEARS ON CENTRIFUGATION. Clear plasma (although very dilute urine may cause erythrocyte lysis).

Haemoglobinuria/myoglobinuria- red colour DOES NOT CLEAR on centrifugation. Red plasma is seen due to Hb/Mb filtering in to urine.

33

URINE GLUCOSE

Urine does not normally contain glucose.
It is filtered and completely reabsorbed.
If too much glucose is present, the reabsorbing capacity may be overwhelmed.
Urine reflects glucose status over the PAST FEW HOURS.
False positives- hydrogen peroxide, bleach, penicillins
False negatives- prolonged dipstick storage, vitamin C, tetracycline, urinary tract infection (bacteria utilise glucose)

-Glucosuria and transient hyperglycaemia- any transient cause that exceeded threshold previously.
-Glucosuria and normoglycaemia- rare tubular defects (Fanconi syndrome- defect in tubule glucose reabsorption)
-Glucosuria and PERSISTENT hyperglycaemia- diabetes mellitus until proven otherwise.

34

KETONES

Ketosis is seen due to negative energy balance- eg. Diabetes mellitus (diabetic ketoacidosis), bovine ketosis, starvation, late pregnancy/early lactation.

Ketones in urine should ALWAYS be addressed.

35

URINE BILIRUBIN

Positive- Normal to see +1 in male dogs.
-Hepatobiliary disease
-Haemolysis
-Urine colour- very dark urine can interfere with reading.

False negative- UV light (converts bilirubin to biliverdin)
-Vitamin C
-Aged samples.

36

URINE SEDIMENT EVALUATION

Cytospin then Romanowksy or Diff-Quick stain.
Look for: CELLS, CASTS, CRYSTALS and OTHER.

37

URINE SEDIMENT- CELLS

-Squamous epithelial cells- common in voided and catheterised samples- both have passed through the lower urinary tract. Flat, angular cells.

-Round/transitional cells- sources include proximal urethra, bladder, ureters, renal pelvis. Round cells with a distinct nucleus.

-Leukocytes- larger than erythrocytes, granular. Greater than 5 white blood cells per 40x field indicates PYURIA (pus in urine).

-Erythrocytes- smaller than leukocytes, with a smooth texture and crenation or area of central pallor.
Greater than 5 red cells per 40x field indicates HAEMATURIA. Low urine pH and low USG can cause red cell lysis.

38

URINE SEDIMENT- CASTS

Formed in renal tubules, a few hyaline or granular casts are normal in the healthy animal.
Casts deteriorate in urine quite quickly- can be hard to detect.
Hyaline, fatty, cellular and granular casts can occur.

39

URINE SEDIMENT- CRYSTALS

Formation of crystals occurs with excess solute, and is temperature and pH dependent.
Presence of crystals does not always mean presence of uroliths as well.
-Struvite- coffin shaped crystals, found in healthy dogs and cats.
-Calcium carbonate- common finding in normal horses, spherical with radiating lines/ovals/dog bone.
-Calcium oxalate monohydrate- Fence picket shape. If seen in an acutely ill cat or dog, ethylene glycol (antifreeze) poisoning should be suspected.

40

URINE SEDIMENT- OTHER

Microorganisms- bacteria, fungi, yeasts.
Is this infection or contamination? Consider- is there inflammation, what was the collection method, what are the clinical signs?
Bacteria may not always be seen, but if bacterial infection is suspected, culture should be taken from urine sample.