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