Transcript Renal Analysis

Renal Analysis
Clinical Pathology
Basic Kidney Structure
• Recall the urinary system from A&P.
• The glomerulus produces an ultrafiltrate of
plasma which is ultimately voided in the
urine.
• Concentration and dilution of urine allows
for a 10kg dog to produced 60 L of
glomerular filtrate/day but less than 1% is
eliminated as urine.
• Reabsorption allows for water to be
attracted by solutes (Na, Cl, urea) in the
medullary interstitium from the distal and
collecting tubules.
Kidneys
• Kidneys are highly susceptible to injury
from drugs or toxins.
• 20-25% of cardiac output each minute
reaches the kidneys delivering large
amounts of any drug in circulation to the
kidneys.
• Nephrotoxic drugs include:
• Acetaminonophen
• Gentamicin
• Arsenic
Definitions
• Azotemia
• An increase in nitrogen containing
waste products such as urea and
creatinine in the blood.
• Uremia
• Sydrome characterized by a
constellation of clinical signs caused by
the retention of wastes normally
excreted by the kidneys.
• An azotemic patient is not always uremic,
however a uremic patient is always
azotemic
Normal Renal Cells
Kidney Assays
• Both urine and blood are used to evaluate kidney
function.
• Functions of the Kidneys:
• Conserve water and electrolytes
• Regulate hydrogen ions to maintain body pH
• Conserve nutrients as glucose and proteins
• Produce renin- enzyme to control blood
pressure.
• Remove end products of nitrogen metabolism:
• Urea-nitrogenous compound that is product
of amino acid breakdown in the liver.
• Creatine
• Allantoin
• Kidney Functions continued:
• Produce Erythropoietin
• Produce Prostaglandins which:
• stimulate contractility of uterine and
other smooth muscle
• lower BP
• regulate stomach acid secretion
• regulate body temperature
• platelet aggregation
• control inflammation
• activate Vitamin D.
Blood Urea Nitrogen (BUN)
• BUN levels used to evaluate kidney
function based on ability of kidney to
remove nitrogenous waste (urea) from
blood.
• Not sensitive- approximate 75% of kidney
tissue must be nonfunctional for elevated
levels.
• Used as a screen for renal disease in any
ill patient, especially those vomiting, wt.
loss, chronic nonregenerative anemia,
pu/pd, anuria/oliguria, chronic UTI, or
dehydration.
BUN Continued
• Normal animals BUN is filtered out of plasma by
renal glomeruli and some excreted in urine.
• Normal BUN for dog is 10-30 mg/dl.
• Handling:
• Hemolysis has little effect
• High protein diet can increase BUN due to
increased breakdown of Amino Acids
• 18 hour fast is recommended
• Contamination with urease-producing bacteria
(staph aureus, proteus, klebsiella) may result in
decomposition of urea-prevent by analysis
within several hours of collection or refrigerated
sample.
• Can store for 8 hours at 20˚ C
Creatinine
• Metabolite of creatine
• Creatine stores energy in muscles in the form of
phosphocreatine.
• Creatinine is formed by the decomposition of
creatine.
• Creatinine in the blood is filtered through the
glomeruli and eliminated in urine
• Can also be found in sweat, feces, and vomitus.
• Not very accurate indicator of kidney function
(same as BUN)
• Normal creatinine is 1-2 mg/dl
• Not affected by a high-protein diet
• Increased BUN and
normal to low
Creatinine
• Early prenatal
azotemia
• High protein diet
• GI hemorrhage
• Tetracycline or
corticosteroid
administration
• Fever
• Severe muscle trauma
• Decreased muscle
mass
• Increased Creatinine
and normal to low
BUN
• Hepatic insufficiency
• PU/PD
• Low-protein diet
• Myositis/muscle
trauma
• Cooked meat diet
Phosphorus
• Levels may increase in patients with
decreases in GFR (Glomerular filtration
rate) similar to BUN and Creatinine
concentrations.
• Controlling the patients with
hyperphospatemia is important in patients
with chronic renal failure to combat renal
secondary hyperparathyroidism
Sodium Sulfanilate and PSP
Clearance
• Sodium Sulfanilate
• Older veterinary test that is no longer used but
was easily performed.
• Replaced by endogenous creatinin clearance
test.
• Na sulfanilateremoved only glomerular filtration
in dogs
• Phenosulfonpthalein (PSP)
• Excreted by renal tubules
• Measures renal blood flow
• Requires 2/3 of nephrons to be nonfunctional
Endogenous Creatinine Clearance
• A natural tracer of glomerular filtration
• Measures blood creatine and accurate, timed urine collection
via catherization, total volume of urine produced is measured
in 24 hours.
• Clearance= Urine volume (in mL) x urine creatinine (mg/dl)
divided by time (min) x serum creatinine x weight
• Renal disease is the major cause of decreased creatinine
clearance although decreased cardiac output may also be
responsible.
• Normal values:
• Dogs: 2.4-5.0 ml/min/kg
• Cats: 1.9 to 5.0 ml/min/kg
Modified Water-Deprivation Test
(Vasopressin Response)
• Use in patients with pu/pd
• Vasopressin or Antidiuretic hormone (ADH) from
neurohypophysis signals kidneys to retain water
• Targets the renal collecting duct
• Give ADH to test for
• Failing kidney function
• Psychogenic polydipsia
• Nephrogenic diabetes insipidus
• If kidney does not respond to ADH
• Neurogenic diabetes insipidus
• If ADH is not released
• Hyperadrenocorticism
Water Deprivation Test
• Trick is to safely dehydrate the patient until
a stimulus for endogenous ADH release
(5% of body weight loss).
• Monitor patient by weight loss, clinical
signs of dehydration, and urine specific
gravity
• Continued diuresis and dilute urine
indicate a lack of endogenous ADH or
unresponsive nephrons
• In dogs with kedney failure,
unresponsiveness precedes
azotemia
Water Deprivation Test
Contraindications
• Dehydration- will risk hypovolemia and
shock.
• Azotemia- already attests to kidney
dysfunction.
• Diabetes insipidus- dangerous and
useless
Urine Protein/Creatinine Ratio
• Quantiative assessment of renal proteinuria is of
diagnostic significance in renal disease.
• Based on concept that tubular concentration of
urine increases both urinary protein & creatinine
equally.
• Canine: 5-10 ml urine by cystocentesis and protein
and creatinine concentrations are determined
• Normal: less than 1
• Nephrotic syndrome: ratio is greater than 1
• Severe glomerulonephritis: ratio is greater than
10
Tests of Glomerular Function
(GFR)
• Assessed by clearance of radioactive
isotopes
• Primarily used in research due to
complexity
Functional Clearance of
Electrolytes (FC)
• Na, K, P, and Cl is increased with renal
damage
• Tests allow for differentiation between
prerenal problems and renal failure
• Measure electrolyte in plasma and urine
and creatinine in both
• If results are normal, issue is prerenal
• If increases the is renal