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88 Cards in this Set

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This is the principal end product of protein catabolism and make sup one half of the total urinary solids
urea
Where urea is synthesized?
liver
Why does the steady state urea level vary inversely with GFR?
because it is excreted principally by glomerular filtration
What is the serum marker of urea level?
BUN (blood urea nitrogen)
Normal BUN values
8-20 mg/dl
Normal Serum Creatinine values
0.6- 1.2 mg/dl
A product of muscle metabolism produced at a relatively constant rate and cleared by renal excretion
creatinine
Usual means of estimating GFR
Creatinine Clearance
What is the normal BUN: Creatinine Ratio?
10:1 RATIO
Will the BUN: Creatinine Clearance increase or decrease in pre renal and post renal azotemia?
increase
Will the BUN: Creatinine Clearance increase or decrease in intrinsic renal diseases, such as acute tubular necrosis and acute interstitial nephritis?
decrease
Does the BUN: Creatinine Ratio increase of decrease with dehydration?
can increase to 20:1 or higher
What is the term used for the amount of filtrate formed by both kidneys per minute?
Glomerular Filtration Rate
Normal GFR
100-120 ml/min
Three factors that GFR relies on
renal auto regulation, neural regulation, and hormonal regulation
What is GFR directly related to?
the pressures that determine the net filtration pressure
What are the 2 main GFR regulation mechanisms?
control of blood flow in and out of the glomerulus by changing diameter of the afferent and efferent arterioles AND control of glomerular surface area via contraction or relaxation of mesangial cells
Factors that GFR depends on
body size, age, and physiologic state
How is GFR measured?
by determining the plasma concentration and excretion of a marker substance
What is the “gold standard” for measuring GFR?
to use the clearance of injected carbohydrate inulin
What is the Cockcroft and Gault used for?
equation used to estimate Creatinine Clearance when a 24 hr urine sample cannot be collected.
Cockcroft and Gault equation
CrCl= (140-age) x weight (kg)/ PCr x 72
When is the newer MDRD (Modification of Diet in Renal Disease) method more useful in calculating GFR?
helpful when patient is older, obese; also corrects for sex and black patients
What population are the Schwartz formula and Counahan-Baratt formula used for to calculate creatinine clearance?
peds
What is the fractional excretion of sodium (FENa)?
amount of sodium actually excreted by body relative to amount filtered by kidneys
When is the FENa calculation done?
when suspecting acute renal failure
When is the FENa most accurate?
when a patient is oliguric (urine volume less than 400 ml/day)
What concentrations is the FENa calculation based on?
concentration of sodium and creatinine in blood and urine
Normal level of Leukocyte Esterase found in urine
none
What is leukocyte esterase?
enzyme produced by neutrophils
If there is a positive leukocyte esterase, what does it suggest?
bacteria
What can cause false positive leukocyte esterase?
squamous cells and vaginal secretions
What can cause false negative leukocyte esterase?
glycosuria, concentrated urine, drugs (TCN, cephalexin), not waiting long enough
Normal level of nitrite in urine
none
If nitrites are positive, consider what?
bacterial infection
What sample is most reliable for nitrites?
first morning void
When can you see a false positive for nitrites in urine?
contaminated sample and gross hematuria
Why is nitrite an indicator for bacteriuria?
because many gram negative bacteria can reduce nitrate to nitrite
This is often the first sign of renal disease
proteinuria
scoring scale for proteinuria
negative thru 4 +
What proteins are dipsticks most sensitive to?
albumin; may not detect other proteins like Bence Jones
What is urinary pH useful for diagnosing?
urinary tract infections, urinary stone disease, and renal tubular acidosis
Urinary pH range
5.0 to 8.0 (usually 5.5-6.5)
What does a urine blood test measure?
intact erythrocytes, free hemoglobin, and myoglobin
If a dipstick is positive for blood, what is needed to confirm?
microscopic evaluation
What can cause a false positive blood test?
menses, concentrated urine
What can cause a false negative blood test?
high ascorbic acid intake
Normal range specific gravity of urine
1.003- 1.030
When are higher values of urine specific gravity seen?
dehydration and shock
When are lower values of urine specific gravity seen?
overhydration or impaired ability to concentrate urine
What is specific gravity useful for?
assessing hydration status and also concentrating status of the kidneys
What is ketone lab used for?
it detects acetic acid and is used to screen for ketosis and diabetic ketoacidosis
Usual level of ketones in urine
none
What can cause a false positive ketone lab?
fasting, carb free diets, dehydration, post exercise, pregnancy, drugs like levodopa
Normal urobilinogen
1-4 mg/day
What conditions will lead to increased urinary levels of urobilinogen?
hemolytic processes or hepatic disease
Normal level of bilirubin in urine
usually none detected
If urine bilirubin is positive, what does it indicate?
increased serum bilirubin
Normal urine glucose level
none
If urine glucose is positive, screen for what condition?
diabetes mellitus
How many high powered fields must be examined in microscopic urinalysis for diagnosis?
at least 10 high power fields
What is the purpose of examining centrifuged urine sediment under a microscope?
showing evidence of renal disease versus lower urinary tract infection; and for indicating the type and activity of a renal or systemic condition
How many RBCs must be in a high power field to be considered significant>
3 or more
What does dysmorphic or irregularly shaped RBCs in urine indicate?
nephritic syndrome
What does round or normal RBCs in urine indicate?
disease along epithelial lining of tract
What is considered significant pyuria?
5 or more leukocytes per high power field
What does pyuria indicate?
injury to the urinary tract (may or may not be infection); can also be due to stones, strictures, neoplasm, GU tuberculosis, or interstitial nephritis
What conditions cause sterile pyuria?
GU Tb and analgesic nephropathy
What does the presence of squamous epithelial cells mean?
contaminated sample---requires repeat collection and testing
If transitional epithelial cells are noted in urine, what do they suggest?
they may be in normal urinary sediment, but if seen in large numbers worry about neoplasm
Most common yeast seen in urine
Candida albicans
What is typically observed when Candida albicans is present?
budding and clumping
What can be used to identify trichomonas?
pear shape and flagella
Where are casts formed?
in the distal tubules and collecting ducts
Casts are formed as a result of what type of precipitation?
Tamm-Horsfall mucoprotein precipitation
How are casts named?
based on their shape and origin
When are hyaline casts seen?
in concentrated urine, febrile disease, after strenuous exercise, and during the course of diuretic therapy
What do red cell casts indicate?
intraparenchymal bleeding
What type of casts are the hallmark of nephritic syndrome?
red cell casts
Conditions that you might see white cell casts in.
acute pyelonephritis and acute interstitial nephritis
What condition do you see tubular casts in?
acute tubular necrosis
What do tubular cell casts consist of?
dense accumulation of sloughed tubular cells
AKA “muddy brown” casts
granular casts
What condition may granular casts represent?
acute tubular necrosis, although nonspecific
What are broad, waxy casts indicative of?
statis--- they form in tubules that have become atrophic and dilated due to chronic parenchymal disease
Causes of increased BUN level
acute and chronic renal failure, urinary obstruction, dehydration, reduced renal perfusion, accelerated catabolism
Causes of decreased BUN level
overhydration, increased renal perfusion, restriction of dietary protein, and liver disease
conditions that usually cause increased serum creatinine
acute or chronic renal failure, and urinary tract obstruction; also increase with increased meat intake, increased muscle mass, and some meds