Renal system- diagnostics

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mrman
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119080
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Renal system- diagnostics
Updated:
2011-11-26 20:06:23
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Renal system
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Renal system- diagnostics
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  1. Where filtration occurs
    Glomerulus
  2. unfiltered blood
    in renal artery
  3. filtered blood
    in renal vein
  4. tests for kidney function based on 3 factors
    • 1. glomerular function
    • 2. glomerular/tubular damage
    • 3. tubular function

    *estimate gross kidney function via blood and urine
  5. Risk factors for renal disease
    #1 DM and HTN: more than 50% of ESRD

    #2 CV disease

    Infection ->glomerulonephritis (strept pyogenes)

    genetic -> PCKD
  6. S/Sx renal disease
    • -nonspecific malaise
    • -HA
    • -N/V
    • -flank pain
    • -dysuria (burning), oliguria (little), anuria (none)
    • -Discolored/malodorous urine
    • -rash
    • -HTN
    • -unexplained electrolyte disturbance (elderly)
    • -abnormal labs
  7. Azotemia
    • -Nitrogen retention
    • -elevated BUN
    • -prerenal, postrenal, renal

    -can live for awhile
  8. Uremia
    • -Urea retention
    • -Occurs with symptomatic ESRD
  9. -needs dialysis
  10. Chronic renal failure
    • -reduced renal function for >3mo
    • -most common
    • -results from multiple conditions: DM, HTN
  11. Prerenal area of damage
    • -problems occur before kidney
    • -causes decreased blood flow to kidney
    • (stenosis, artherosclerosis, HTN)
    • -decreases filtration rate
    • -prdominant cause of azotemia
  12. Renal area of damage
    • -damage to renal parenchyma
    • -glomerulonephritis
    • -PCKD
    • -tubular necrosis
  13. Postrenal area of damage
    • (excludes renal vein)
    • -occurs after kidney; usually obstruction in ureters, bladder, urethra
  14. Creatinine
    waste product from hydrolysis of creatine and phosphocreatine in muscle

    • -filtered at glomerulus
    • -secreted at proximal tubules
  15. Creatinine levels
    kidney function decline = increase in serum, decrease in urine

    • -naturually higher in males
    • -more sensitive than BUN

    -Always compare to previous values

    -levels double with 50% decrease in GFR
  16. Non-renal causes of creatinine increase
    • -creatine supplements
    • -muscle wasting
    • -temporarily w/marathon runners
  17. BUN
    Blood urea nitrogen

    • -product of protein and nucleic acid catabolism
    • -evaluates glomerular function
    • (urea synthesized in liver and >90% excreted through kidneys)

    -more volatile than creatinine; need to use ratio
  18. BUN levels
    • -increase with impaired kidney function
    • -declines with liver failure or malnutrition
    • -normal <20 mg/dL

    • -varies daily
    • -affected by blood in GI tract, protein intake, hydration
    • (dehydration increases BUN)

    • increased in prerenal/postrenal azotemia
  19. BUN/creatinine ratio
    • -to differentiate prerenal/postrenal azotemia from renal azotemia
    • -ratio is used w/abnormality, not alone

    Normal = 10:1, and levels rise proportionally

    • Prerenal azotemia = 20:1 +
    • BUN increases faster w/ bigger increase (decr. renal perfusion)

    Renal azotemia = 10:1; elevation together

    Early postrenal obstructions = 20:1; early, acute rise; can evolve into renal azotemia from pressure damage, then ratio returns to 10:1
  20. GFR
    glomerular filtration rate

    • -direct measure of renal function
    • -body fluid cleared by kidneys per time unit using estimated body surface area

    • -based on creatinine levels
    • -good early indicator of disease w/changes

    -varies according to age, sex, body size (muscle mass)
  21. Estimated (eGFR)
    • based on creatinine values, age, gender, race
    • (females have 25% less; naturally higher in AA)

    • -Decrease precedes onset of kidney failure
    • -more sensitive and specific than BUN
    • (good to use w/HTN and DM as early predictor)

    -presistent decrease is diagnostic criterion for CKD
  22. eGFR levels
    -naturally decrease with age

    <60 = onset of CKD; follow closely; increased risk of CV disease

    <30 = get on meds; refer to nephrology

    <15 = need dialysis; risk factors for other diseases

    *treat these levels seriously; no variation like with BUN and creatinine
  23. Creatinine clearance
    if you can't get good eGFR

    • -based on muscle mass
    • -tends to overestimate GFR
    • -sensitive test to warn of kidney failure
  24. Drawbacks of creatinine clearance test
    • -depends on accurate 24hr urine collection
    • -affected by large amounts of meat ingestion
  25. calculating creatinine clearance
    uses weight, age, serum creatinine
  26. Urinalysis/urine dip
    • -evaluates physical and chemical properties
    • -can evaluate multiple disease states

    -use clean-catch and chemstick
  27. Timed urinalysis
    • -2hrs
    • or
    • -24hrs

    • -can evaluated urine output
    • -can confirm presence of abnormality
  28. Urine color
    pigmented by urochrome (product of metabolism)

    • -yellow variations = state of hydration
    • -amber variations = urine concentration or specific gravity
  29. Urine odor
    fruity (acetone) = diabetes (ketosis)

    fould odor = UTI (urea splits to ammonia)
  30. Urine appearance
    • clarity of specimen
    • normal = clear

    • cloudy:
    • -normal if change in urine pH
    • -WBCs, RBCs, bacteria
    • -clear, hazy, cloudy, turbid, milky
  31. Specific gravity
    • -measures kidney's ability to concentrate urine
    • -measures density of urine against density of distilled water

    • 1.001 - 1.010 Dilute
    • 1.010 - 1.025 Normal
    • > 1.025 Concentrated

    order urine osmolality to confirm
  32. Urine pH
    • -renal tubules maintain acid-base balance
    • -tubular secretion of H+ and NH4+

    • normal = 4.0-8.0
    • avg = 5.0-6.0
  33. Blood in urine
    Negative = normal

    • Hematuria
    • Hemoglobinuria

    -on urine dipstick, not distinguishable btn hematuria and hemoglobinuria
  34. Hematuria
    • RBCs in urine
    • -majority of disorders within urinary tract
    • -UTI, kidney stones, infection
  35. Hemoglobinuria
    • Hemoglobin in urine
    • -majority of disorders outside urinary tract that cause hemolysis

    -sick pt; ER setting
  36. Protein in urine
    -measures albumin and globulins

    • -may be first sign of renal disease
    • (even before symptoms)
    • -single most important indication of renal disease

    -order 24hr urine for protein if (+) on dip
  37. Microalbumin
    • -precursor to albumin
    • -ordered on DM pts

    • -detects very small amount of protein in urine
    • -early detection for kidney disease

    • ordered anually = type 2 DM
    • ordered anually = type 1 DM after 5 yrs

    -if (+), confirm in 3mos
  38. (+) microalbumin at 3 months retest
    diagnosis of nephropathy

    -ACE-I or ARB can slow/prevent
  39. Glucose in urine
    Normal = negative

    check serum glucose level if positive in urine
  40. Ketones in urine
    Normal = negative

    -particularly important with Type 1 to evaluate ketoacidosis and diabetic coma

    -can also appear with Atkins diet
  41. Nitrites in urine
    Normal = negative

    • -nitrate converted to nitrite by bacteria (gram (-) bact)
    • -usually used to screen UTI
    • -elderly, symptomatic pts, pregnant pts
  42. Leukocyte esterase
    Normal = negative

    • -esterase released by the leukocytes into the urine
    • -positive = UTI

    • false-positive from:
    • -vaginal discharge/infection
    • -bleeding
    • -heavy mucus
  43. UTI abnormal tests
    • nitrites
    • leukocyte esterase
  44. Bilirubin
    Normal = negative

    • -even trace amounts are abnormal
    • -early sign of liver disease or biliary obstruction

    -increases with any disease that causes increased serum conjugated bilirubin
  45. Urobilinogen
    • -bilirubin transformed through bacterial enzymes into urobilinogen in intestines
    • -colorless
    • -trace amounts are normal

    • -very sensitive test for liver dysfunction
    • -elevation = liver disease or hemolytic d/o
    • -absence = obstruction of bile duct
  46. Urine sediment exam
    Normal = no casts

    • WBC cast = renal parenchymal infection
    • Broad/waxy cast = collecting tubule dysfxn/acute renal failure

    RBC cast = hemorrhage in nephron
  47. Urine culture
    -to diagnose bacterial UTI

    -ordered at urine C&S
  48. Urine volume
    -direct measure of kidney function

    Normal = 1200mL in 24hrs

    (range 600-2500mL)
  49. Oliguria
    decreased ouput

    100-400 mL/24hrs
  50. Anuria
    severely decreased

    <100 mL/24hrs
  51. Polyuria
    increased output

    >3000 mL/24hrs

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