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Lab Diagnosis > Renal Function Tests > Flashcards

Renal Function Tests Flashcards

1
Q

what 3 things does renal fxn testing provide information of?

A
  • renal blood flow
  • GFR
  • tubular fxn
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2
Q

why is it imperfect?

A

-various factors other than damage to renal parenchyma can influence results

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3
Q

what are the 2 definitions of renal disease?

A
  • presence of histological lesions but does not specify any degree of renal dysfxn
  • 75% of nephrons destroyed/lost but doesn’t imply underlying histological lesions
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4
Q

what 4 tests are used to test clearance? what 1 for tubular fxn?

A 
clearance:
-BUN
-serum creatinine
-creatinine clearance
-albumin creatinine ratio
tubular fxn
-fractional excretion of Na+
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5
Q

the ideal substance to measure GFR would be what 8 things?

A
  • freely filtered at glomeruli
  • not bound to plasma
  • not be metabolized
  • be non-toxic
  • be excreted only by kidneys
  • neither reabsorbed nor secreted
  • stable in blood & urine
  • easily measured
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6
Q

where does BUN come from? how much is filtered by glomerulus? how much is reabsorbed?

A
  • protein catabolism via urea cycle in liver

- 40% reabsorbed so urea clearance is about 60% of true GFR

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7
Q

what substance do you test for BUN levels? what does it evaluate and indicate?

A
  • serum/plasma testing (CMP or BMP)
  • evaluates liver fxn
  • rough indicator of GFR & renal blood flow
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8
Q

what factors can interfere with BUN?

A
  • protein intake
  • muscle mass
  • pregnancy
  • hydration levels
  • liver disease
  • drugs
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9
Q

what are the normal levels of BUN for an adult? critical value? causes for decreased values?

A

adult value: 10-20 mg/dl
critical value: >100 mg/dl (serious impairment of renal fxn)
decreased values due to: fluid overload, malnutrition, severe liver disease

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10
Q

what is azotemia? pts with azotemia will have what?

A

azotemia: increased concentration of non-protein nitrogenous waste products
pts w/azotemia will have increased BUN

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11
Q

prerenal causes of increased BUN? what percentage of acute renal failures (ARF)?

A 
causes:
-low BV: shock, burns, dehydration
-CHF, MI
-GI bleed
-too much protein
-high protein catabolism: starvation
-sepsis
55% of ARFs
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12
Q

renal causes of increased BUN? %age?

A

causes: renal dz
-glomerulonephritis
-pyelonephritis
-tubular necrosis
-nephrotoxic drugs
40% of ARFs

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13
Q

postrenal causes of increased BUN? %age?

A

causes:
-obstruction of ureters: stones, tumors, congenital
-bladder outlet obstruction: prostatic hypertrophy, cancer, congenital
5% of ARFs

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14
Q

what is serum creatinine? what do the levels depend on? so only when do you see this? more or less stable than BUN?

A
  • catabolic product of creatine phosphate from skeletal muscle
  • levels depend on muscle mass; only see fluctuation in muscle mass with muscle-wasting pathology
  • more stable than BUN
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15
Q

what happens to creatinine in the kidneys in terms of filtration?

A

-almost completely filtered by kidneys but also secreted by PCT

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16
Q

when does serum creatinine rise in relation to BUN? what does elevation suggest? who normally has lower levels?

A
  • creatinine levels raise later than BUN
  • elevation= chronic disease process
  • young and elderly due to lower muscle mass
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17
Q

what are the normal levels? what is creatinine used to diagnose? are its levels affected by liver fxn?

A

male: 0.6-1.2
female: 0.5-1.1
used to diagnose impaired renal fxn minimally affected by liver fxn unlike BUN

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18
Q

what is the rectangular hyperbola?

A
  • large change in GFR early in renal dz cause sm changes in BUN or creatinine
  • small changes in GFR late in renal dz cause big changes in BUN or creatinine
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19
Q

what BUN/creatinine ratio is indicative of prerenal azotemia? renal azotemia?

A

prerenal ratio: >20:1

renal ratio: 10-20: 1

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20
Q

in prerenal dz what will rise first urea or creatinine? in renal dz? will you see proteinuria in prerenal or renal dz?

A

prerenal: disproportionate rise in urea
renal: risk together
proteinuria in renal dz

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21
Q

as GFR goes down what goes up?

A

serum creatinine

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22
Q

eGFR is inaccurate when?

A
  • vegetarian
  • pregnant
  • malnourished
  • > 70 or <18
  • muscle dz
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23
Q

to test creatinine clearance what test(s) do you need?

A

24 hr urine & blood draw during urine collection time

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24
Q

when is CC invalid?

A

GFR decreased to <30% of normal

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25
Q

normal CC values? how much does it decrease by each decade after 20 yo?

A

male: 90-139 ml/min
female: 80-125 ml/min
values decrease 6.5 ml/min each decade after 20

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26
Q

what are 4 factors which affect CC?

A
  • exercise increases
  • pregnancy increases
  • incomplete collection gives false low value
  • drugs
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27
Q

what is great about cystatin C? normal range?

A

-filtered by glomerular membrane & metabolized by PTs
-estimates GRF independent of gender, age, race, muscle mass, cirrhosis, no need to correct for height and weight
SUPERIOR TO CREATININE
-adults: 0.54-1.55 mg/L

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28
Q

Ssxs of kidney failure?

A
  • loss of appetite
  • nausea/vomiting
  • edema
  • low back pain
  • decreased urine output
  • fatigue
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29
Q

how does ARF present in terms of hx, kidney size, blood disorders and casts? CRF?

A

ARF: over hours to days, hx of normal renal fxn, kidney size normal, no anemia or casts
CRF: deterioration of renal fxn over time, hx of increased BUN & creatinine, kidney usu sm, anemia usu & casts in urine

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30
Q

tubular fxn test of FENa <1% is what kind of ARF?

A

prerenal

decreased renal blood flow triggers renin-angiotension pathway= kidneys conserve Na+

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31
Q

tubular fxn test of FENa >2% is what kind of ARF?

A

renal

damaged tubules can’t effectively conserve Na

32
Q

what is the most important indicator of renal dz?

A

PROTEINURIA

normal range is <150 mg/24 hrs

33
Q

proteinuria 150-500mg/24 hrs indicates what? >2000 mg/24 hrs? >3500 mg/24 hrs?

A

150-500 mg/24 hrs can be fxnal if asx
>2000 mg/24 hrs indicates glomerular cause
>3500 mg/24 hrs indicates nephrotic syndrome

34
Q

what can cause proteinuria in absence of structural abnormality in kidneys?

A

CHF! can also occur in pre-eclampsia, eclampsia, HTN, heavy metal toxicity, solvents

35
Q

what is more accurate than 24 hr urine protein? what urine sample would you prefer? normal ratio?

A

urine protein to creatinine ratio is more accurate
use 1st morning void
ratio: <0.2 g protein/g creatinine

36
Q

what population is microalbuniuria used with?

A

pts w/DM and/or HTN for detection of kidney dz

37
Q

what is urine albumin to creatinine ratio used for?

A

detect microalbuniuria

diagnose & monitor kidney damage in pts w/type 1 DM for 5 yrs or more or type 2 DM

38
Q

what are kidney stones known as?

A

nephrolithiasis
urolithiasis
renal calculi

39
Q

what # of ppl get kidney stones in their life? who is it rare in?

A

1 in 20 will get them at some pt

rare in children, when present often associated w/specific metabolic disorder or anatomic abnormalities

40
Q

what 3 renal pathologies are common to occur around puberty or in mid-teens?

A

cystinuria
idiopathic calcium oxalate urolithiasis
primary hyperparathyroidism

41
Q

when do kidney stones form?

A

high level of minerals: calcium, oxalate or uric acid in urine or when there is a lack of citrate in the urine or insufficient water

42
Q

what normally prevents formation of crystals?

A

citrate, magnesium & pyrophosphate

43
Q

what 4 things might be done to evaluate why someone is forming stones?

A
  1. chemistry panel (calcium & bicarb levels)
  2. PTH if elevated serum Ca2+
  3. UA including pH and urine culture
  4. urinalysis (pH and sediment exam)
44
Q

pH >7.5 is compatible for what kind of stones?

A

struvite or calcium phosphate

45
Q

<5.5 is compatible for what kind of stones?

A

uric acid or cystine stones

46
Q

what stones are not pH dependent?

A

calcium oxalate

47
Q

what factors contribute to calcium oxalate stones?

A
  • low urine volume

- high concentrations of calcium & oxalate

48
Q

what factors contribute to calcium phosphate stones?

A
  • alkaline urine

- high urine calcium concentrations

49
Q

what can increase 24 hr urine calcium levels?

A
  • primary hyperparathyroidism
  • vitamin D excess
  • corticosteroid tx
  • PTH producing tumor
  • cushing’s syndrome
  • sarcoidosis, TB
  • osteoporosis
  • metastatic tumors in bone
  • renal tubular acidosis
50
Q

what can decrease 24 hr urine calcium levels?

A
  • hypoparathyroidism
  • vit D deficiency
  • calcium malabsorption
  • renal failure
51
Q

pts w/tendency to calcium oxalate nephrolithiasis appear to ____ & ___ a high proportion of dietary ____ in the urine

A

absorb & excrete

oxalate

52
Q

indications of high oxalate in urine? 3

A
  • pts w/surgical loss of distal ileum (Crohn’s dz)
  • IBS (1-3% of IBS pts form)
  • jejunal bypass
53
Q

normal oxalate values?

A

males: 7-44 mg/24 hrs
females: 4-31 mg/24 hrs
children: 13-38 mg/24 hrs

54
Q

what other factors can increase 24 hr urine oxalate?

A
  • ethylene glycol ingestion
  • genetic disorder
  • pancreatic dz
  • liver cirrhosis
  • pyridoxine deficiency
  • sarcoidosis
  • celiac dz
55
Q

what other factors can decrease 24 hr urine oxalate?

A
  • renal failure

- high urinary Ca2+

56
Q

what is hypocitraturia?

A

urine citrate excretion <434 mg in men

57
Q

when will you see hypocitrturia?

A
  • IBD
  • intestinal malabsortion
  • renal tubular acidosis
58
Q

what is citrates role?

A

plays a role in inhibiting Ca2+ formation and prevents stones

59
Q

what does a high protein diet cause?

A

increase acidosis= release Ca2+ from bones into urine= decrease release of citrate in urine to buffer acidosis= increase stone formation

60
Q

normal levels of uric acid?

A

250-750 mg/24 hrs

61
Q

where does uric acid come from? how much is excreted by kidneys? where does the rest go? elevated levels can cause what?

A

breakdown product of purine metabolism in the liver
75% excreted, remained via GI tract & out
elevated levels can cause gout

62
Q

uric acid stones form with what pH? what body state? what can it be linked to?

A
  • unusually low pH & hyperuricosuria
  • increased risk in obese, metabolic syndrome
  • may be linked to insulin resistance
63
Q

when do you see increased uric acid?

A
  • gout
  • metastatic cancer
  • multiple myeloma
  • leukemia
  • cancer chemotherapy
  • high purine diet
  • lead toxicity
64
Q

when do you see decreased levels of uric acid?

A
  • renal disease
  • eclampsia
  • chronic alcoholism
65
Q

what are triple phosphate crystals? what kind of urine are they present in? what can precipitate these? what kind of stones do they form?

A
  • magnesium ammonium phosphate
  • alkaline urine
  • commonly seen in pts w/UTI
  • struvite stones
66
Q

what 6 things do you do when a pt presents with recurrent nephrolithiasis?

A
  1. stone analysis
  2. serum & blood tests (Ca, PTH, vit D, electrolytes)
  3. urine dip & microscopic exam (pH, sediment)
  4. culture
  5. 24 urine collection (volume, creatinine, Ca oxalate, Na, citrate, uric acid, cystine)
  6. helical CT w/o contrast
67
Q

where do homovanilic acid and vanillylmandelic acid come from?

A

end products of catecholamine metabolism

68
Q

what can vanillylmandelic acid and homovanilic acid be used to diagnose?

A

-pheochromocytoma, neuroblastoma, ganglioneuroma, ganglioneuroblastoma & rare adrenal tumors

69
Q

what is a collage which provides tensile strength to bone matrix of bone? when is it released? what void catches the most?

A

cross-link of type I
collagen
released during bone resorption & excreted unchanged into urine
2nd morning void sample used

70
Q

what will increase deoxypyridinoline?

A
  • osteoporosis
  • osteolytic metastatic cancers
  • hyperthyroidism
  • see in children
  • osteomalacia
  • hyperparathyroidism
  • multiple myeloma
  • paget’s dz
  • long-term steroid use
  • cushing’s
71
Q

what is the significance of N-telopeptides?

A

response can be determined w/in 3-6 mo rather than 1-2 yrs you have to wait btw DEXAs so can see bone loss earlier

72
Q

when do you see HCG (dx and timing)? where does the hormone come from?

A

pregnancy, about 10 d after conception
comes from placental trophoblast
some cancers can also produce this hormone

73
Q

when will you see increased HCG?

A
  • normal pregnancy
  • ectopic pregnancy
  • germ cell tumors of ovaries or testes
  • hydatidiform mole- pregnancy that turns into cancer
  • choriocarcinoma
74
Q

when are drug tests used?

A
  • employers may use before hiring
  • to test appropriateness of prescribing controlled substance for pt
  • before increasing dose of analgesic medications
  • before referring to a pain or addiction specialist
75
Q

what are the 2 drug screening tests?

A

immunoassay: used as screening, rapid, inexpsensitive, Abs to detect drugs, good for detecting marijuana and cocaine
gas chromatography/mass spec: confirmatory test, expensive, time consuming, more accurate

76
Q

what can cause an immunoassay to have false negatives?

A
  • dilute urine
  • time
  • labs established limits
  • sample tampering
  • negative result may not be correct
  • many other things can also cause false positive

Lab Diagnosis (5 decks)

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