biomarkers of urine Flashcards by Marissa Bobay

_____ & _____ are required to obtain most reliable results from diagnostic test

high sensitivity
&
high specificity

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_____ is clinically important bc it reflects disease prevalence

PPV

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what estimated % of prescribed tests are unnecessary

40-60%

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consequences of not understanding testing limitations

-misunderstand test results
-overestimate accuracy of test results
-blind to false-positives
-prescribe unnecessary tests

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what 2 tests are the preliminary diagnostic approach for kidney function

strip test
&
microscopic analysis

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most commonly used endogenous marker for GFR

creatinine

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normal GFR for adult male

90 - 120 ml/min

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what is Jaffe’s reaction

creatinine (in alkaline medium) + picric acid
–>
Janovsky complex (orange)

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what is the common chemical method for creatinine estimation

Jaffe’s reaction

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why is Jaffe’s reaction/test less specific

due to interference w other biomolecules

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what % difference is value from Jaffe’s reaction/test vs actual value

15 - 25% higher than actual value

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what is the enzymatic method for measuring creatinine

creatininase (creatinine amidohydrolase)

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creatininase (creatinine amidohydrolase) mechanism

detection of creatinine is based on hydrogen peroxide generation

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benefit of creatininase (creatinine amidohydrolase)

higher specificity vs chemical method

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ratio of BUN : creatinine in pre-renal disease

20 : 1

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ratio of BUN : creatinine in intrinsic renal disease

10 : 1

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is chemical method or enzymatic method better for assessing renal function

enzymatic method

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how much creatinine do muscles add to blood per day

1800 mg /day

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how much creatinine is filtered & excreted in urine per day

1800 mg /day filtered

1800 mg /day excreted

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how does creatinine handling by the body change if GFR decreases by 50%

amount excreted decreases by 50%

creatinine is retained ([plasma creatinine] increases over time)

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_____ can be used to estimate GFR instead of creatinine clearance over 24 hrs

Pcr [plasma creatinine]

increasing GFR = _____ Pcr ([plasma creatinine])

decreasing

what does eGFR mean

estimate GFR using only Pcr [plasma creatinine]

disadvantage of using Pcr to estimate GFR

GFR has to decrease significantly in order to see increases in Pcr (so mainly useful for advanced kidney disease)

individual factors you can correct for when calculating GFR

weight age sex height race

MDRD when calculating GFR stands for

(Modification of Diet in Renal Disease)

MDRD equation to calculate GFR contains what components

Pcr age sex race

factors that DECREASE Pcr

older age female muscle wasting vegetarian

factors that INCREASE Pcr

muscular carnivores

CKD-EPI equation to calculate GFR contains what components

Pcr age sex

what is the good thing that the CKD-EPI equation does

removes race (bc it's a social construct)

what protein can be used combined with creatinine to help determine GFR

cystatin

GFR estimates are most accurate when serum creatinine levels are _____

high

5 stages of CKD (just numbers)

(ml/min) stage 1) eGFR > 90 stage 2) eGFR 60 - 89 stage 3) eGFR 30 - 59 stage 4) eGFR 15 - 29 stage 5) eGFR < 15

5 stages of CKD (descriptions)

stage 1) normal kidney function & > 3 months of proteinuria (mostly albumin) stage 2) mild loss of kidney function & > 3 months of proteinuria (mostly albumin) stage 3) mild to severe loss of kidney function stage 4) severe loss of kidney function stage 5) ESRD, kidney failure

what radiolabeled non-ionic molecule's clearance can be used to also measure GFR

iohexal

advantages of blood iohexal use

-easy to prick finger -cheap -no interference w endogenous biomolecules (exogenous tracer) -accurate at specific time points -available in US (unlike inulin)

what is new current "gold standard" for GFR measurement

iohexal

disadvantages of blood iohexal use

-requires bolus IV injection & time for equilibrium

advantages of serum creatinine use

-endogeonus metabolite -abundant in body -available assays in US

disadvantages of serum creatinine use

-dependent on muscle mass -affected by muscle damage -affected by diet (eating meat) -non-linear relationship w GFR

3 kidney-related factors increase BUN

-kidney disease -dehydration -decreases in renal perfusion

what is Fractional Excretion (FE)

how much solute is excreted in urine relative to the solute's filtered load

equation for FE (using clearance)

% FE = ( (U x Pcr) / (Ucr x P) ) x 100 U: [solute in urine] Pcr: [creatinine in plasma] Ucr: [creatinine in urine] P: [solute in plasma]

equation for FE Na (fractional excretion of Na)

% FE Na = ( (Una x Pcr) / (Ucr x Pna) ) x 100 Una: [Na in urine] Pcr: [creatinine in plasma] Ucr: [creatinine in urine] Pna: [Na in plasma]

normal range of FE Na

1 - 3 %

FE Na elevated value & meaning

> 1 - 3 % acute tubular necrosis

FE Na decreased value & meaning

< 1 % normal, dehydration, or AKI

FE U equation (fractional excretion of urea)

% FE U = ( (Uu x Pcr) / (Ucr x Pu) ) x 100 Uu: [urea in urine] Pcr: [creatinine in plasma] Ucr: [creatinine in urine] Pu: [urea in plasma]

normal range of FE U

50 - 65 %