biomarkers of urine Flashcards
_____ & _____ are required to obtain most reliable results from diagnostic test
high sensitivity
&
high specificity
_____ is clinically important bc it reflects disease prevalence
PPV
what estimated % of prescribed tests are unnecessary
40-60%
consequences of not understanding testing limitations
-misunderstand test results
-overestimate accuracy of test results
-blind to false-positives
-prescribe unnecessary tests
what 2 tests are the preliminary diagnostic approach for kidney function
strip test
&
microscopic analysis
most commonly used endogenous marker for GFR
creatinine
normal GFR for adult male
90 - 120 ml/min
what is Jaffe’s reaction
creatinine (in alkaline medium) + picric acid
–>
Janovsky complex (orange)
what is the common chemical method for creatinine estimation
Jaffe’s reaction
why is Jaffe’s reaction/test less specific
due to interference w other biomolecules
what % difference is value from Jaffe’s reaction/test vs actual value
15 - 25% higher than actual value
what is the enzymatic method for measuring creatinine
creatininase (creatinine amidohydrolase)
creatininase (creatinine amidohydrolase) mechanism
detection of creatinine is based on hydrogen peroxide generation
benefit of creatininase (creatinine amidohydrolase)
higher specificity vs chemical method
ratio of BUN : creatinine in pre-renal disease
20 : 1
ratio of BUN : creatinine in intrinsic renal disease
10 : 1
is chemical method or enzymatic method better for assessing renal function
enzymatic method
how much creatinine do muscles add to blood per day
1800 mg /day
how much creatinine is filtered & excreted in urine per day
1800 mg /day filtered
1800 mg /day excreted
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)
_____ 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 %
