GFR and ERPF Flashcards
extraction ratio (ER)
fraction of substance removed from plasma during one circulation through kidney
extraction ratio measures …
urine elimination and renal retention
what does a ER of 1.0 mean?
1) that the drug is completely removed from circulation in a single pass
= true measurement of RPF
2) or drug is completely retained = ideal for morphology
what RP is best used for ERPF?
MAG3
formula for ER
ER = (arterial concentration of substance - venous concentration of substance)/arterial concentration of substance
which RP is best for morphology?
DMSA
renal clearance
amount of substance that appears in the urine in a given time
formula for renal clearance
renal clearance (ml/time) = ([urine] * vol/min)/[plasma]
which RP is completely filtered by the glomerulus, therefore is good to measure GFR?
DTPA
indications
- monitoring function in renal disease
- monitor renal function throughout course of nephrotoxic drug admin
- eval renal function in live tx donors
- follow up post tx
camera GFR technique
Gate’s Method
- pre-injection counts of syringe on camera
- dynamic imaging for min 6 mins
- post-injection syringe counts
blood sample technique
- single/serial blood sample techniques
- determine time
- compare to standard
Dose required for Gate’s Method
111 MBq
distance the syringe is at for gate’s method
syringe counted 20-30 cm from face of camera
dose for GFR blood sampling technique
370-555 MBq
theory for gfr blood sampling
% of tracer remaining in blood at specific times indicate renal functions – clearance and filtering through kidneys (tracer excreted by kidneys)
high plasma counts = GFR ______
low
low plasma counts = GFR ______
high
four broad stages for GFR measurements
- tracer prep
- tracer admin
- blood sampling
- sample counting
if you draw from the same arm as the injection, what will happen to your GFR?
it’ll make the GFR look lower because your counts might be higher
if you collect the blood sample 30 mins too early, what happens?
plasma counts will be too high = gfr look lower
if you collect the blood sample 30 mins too late, what happens?
plasma counts will be too low = gfr look higher
renal plasma flow
amount of plasma at the glomerulus
formula for effective renal plasma flow
C = U x V/P
RP for ERPF
MAG3
RP for GFR
DTPA
RP for morphology
DMSA
Which of the following are appropriate times for acquiring plasma samples in a multi- sample GFR study?
a. Immediately, 1hr and 3hrs
b. 30 min, 1hr and 2hrs
c. 2hr, 3hrs, and 4hrs
d. 3hrs, 4hrs and 24hrs
c - need at least 1 hr for equilibrium
