Lab Tests For The Kidney Flashcards
What is the normal function of the kidney?
- Homeostasis
- excretion of waste roducts
- water balance
- acid-base balance
- electrolyte balance
- Hormonal
- hemodynamics
- red blood cell production
- bone metabolism
What is filtered rate? what is excreted rate? what does this lead to?
filtered rate (mg/min)= PlasmaX(mg/min) * GFR (ml/min)
excreted rate(mg/min) =urineX (mg/ml) * urine flow (ml/min)
filtered rate=excretion rate
GFR=Urine * Urine flow/ plasma
Clearance= U* V/P
WHat is the equation for clearance? What is X? what are some exogenous markers?
Clearance= Ux* V/Px
Clearance of creatine is used to represent GFR
Characteristics?
freely filtered
non-toxic
not secreted
not reabsorbed
not changed during excretion
Exogenous markers: inulin, Iothalamate, Iohexol
How is creatine produced? WHy is it a good measure of GFR?
Creatine is produced from metabolism of muscle creatine and from dietary meat intake
- released into circulation on a constant basis
- freely filtered
- non-toxic
- secreted-small amount in proximal tubule
- not reabsorbed
- not changed during ecretion
Assuming that the GFR is 120ml/min with a serum creatine of 1mg/dl, what is the difference in GFR between a serum creatine of 4mg/dl and a serum creatine of 5mg/dl?
6ml/min
Creatine quadruples, GFR must decrease to 1/4=30ml/min
Creatine has quintupled, GFR must decrease to 1/5= 24 ml/min
difference between creatine of 4mg/dl and 5 mg/dl is 30 ml/min-24 ml/min=6ml/min
what are the normal values for serum creatine? men, women and children
men= 0.9-1.3mg/dl
women= 0.8-1mg/dl
children= 0.5-1mg/dl
how is creatine related to msucle mass?
- sincre creatine production is largely from muscle creatine, greater muscle mass leads to greater creatine production
- black, men and younger adults have more muscle mass, and blacks also have a higher creatine generation rate
Is creatine an exact measure of calculated kidney function?
- creatine clearance overestimates GFR due to a small amount of secretion in the tubules
- measured clearance requires 24 hours of urine collection
- creatine production is dependent on muscle mass
What is the Cockcroft Gault Formula based on? WHo should you be careful using it on?
- not adjusted for body surface area
Serum Creatine
Age
Weight
Gender
- developed when obesity was less common
- use with caution in obese or edematous people
What is MDRD study equation based on? how does it do at estimating GFR?
Serum creatine
age
gender
race
**It underestimates GFR if the actual GFR is greater than 60 . ml/min/1.73m2
What is the CKD-EPI equation based on?
more accurate with estimated GFR greater than 60ml/min/1.73m2
it is a much more complicated equation
serum creatine
age
gender
race
What is cystatin?
protein produced by all nucleated cells
freely filtered
production seems less affected by age and gender than creatine
new estimating equations based on cystatin C, either lone or with creatine
How is chronic kidney disease defined? At what point do you need dialysis?
GFR<60ml/min/1.73 for >3 months and other evidence of kidney damage
need dialysis when GFR<10ml/min
How do you define acute kidney injury? Can we use the equations about GFR for acute kidney disease? What are early signs?
acute kidney injury occurs over hours to days/acute sustained reduction in renal function/25% increase in creatine
No! the equations only relate for a steady state
so formulas cannot be used, new steady state is needed, serum creatine rises, early signs can be decreased urine output!
What is the RIFLE criteria for stratifying AKI? what is the timeline for it? what is the timeline for the AKIN criteria? what are they both weighted on?
Risk
Injury
Failure
Loss of Funciton
ENd stage renal disease
ovr not more than 7 days
AKIN criteria is within 48 hours
*****they are bosth weighted on urine output and creatine changes
how fast does creatine change during injury?
it takes time for creatine to rise!
typically about 48 hours from time of injury for there to be any change
even if GFR is 0, creatine typically only increases 1-2mg/dl/day therefore it can’t be used for acute well!
creatine is a functional marker of _____
but now we instead are looking for what?
creatine is a function marker of organ damage,
but now we are looking for biomakers which are foot prints of actual organ damage
is it possible to have chronic kidney disease and a normal GFR?
yes!
Total urinary protein should be ________
At what point is it considered nephrotic?
Nephrotic syndrome has low ____ and ______
urinary protein should be less than 150mg/day
urine protein of greater than 3.5g/24 hours is nephrotic
nephrotic syndrome has low serum albumin and edema
what does a urine dipstick show?
a negative and positive reading for protein in the urine by urine dipstick
primarily detects albumin
it is dependent on urine concentration and isnt an actual value, just + marks, it is considered semi-quantitative report for proteinuria
What is microalbuminuria?
- it meads there is moderately increased albumin in the urine
- most of the total urinary protein is made up of tubular proteins
- albumin in the urine is abnormal
- microalbuminuria is defined as
- 30-300mg albumin per 24 hours
- 30-300 mg/albumin/g of creatine
- this is usually below dipstick threshold!!
What are the 2 quantitative tests for proteinuria?
24 hour urine
spot urine sample
WHat is overflow
when you have an increase in protein in the urine that is not albumin
WHen you have increase in albumin in the urine that is due to?
glomerular damage
what are qualitative test for proteinuria?
protein electrophoresis of serum or urine
when done in serum you should see a big spike for albumin, if you see another big spike that is a different protein and is indicative of something making large amounts of protein in the body, for example cancer
