C - Renal Function Flashcards
what is the best measure of kidney function
GFR
what is a normal GFR
120ml/min / 7.2L/hr
3 functions of kidney
waste excretion
metabolic balance including acid:base
water / urine excretion
what is the function of the glomerulus
water and low molecular weight molecules component filtrate, retains high molecular weight molecules
what is the function of the tubules
resorption of glomerular filtrate
by how much does GFR change with each year of life
1ml/min/yr
what can be used to estimate GFR
clearance
what is clearance
volume of plasma that is cleared of a substance per unit time
features of a suitable clearance molecule
not charged
not metabolised
not bound to serum proteins
freely filtered at glomerulus
what is the equation for clearance
C = U x P
what is the gold standard molecule to measure GFR
inulin
why is blood urea not used as a measure of GFR
increased by high protein intake or bleeding
decreased by liver disease and low protein intake
variable resorption by tubular cells
where is creatinine made
muscle cells
what does creatinine clearance depend on
muscle mass, age, sex, ethnicity
can decrease in surgery, starvation, steroid use
how is creatinine related to GFR
plasma creatinine ratio is inversely related to GFR
does a normal plasma creatinine ratio mean GFR is normal
NO - there is a lag between GFR dropping and plasma creatinine increasing
what is the cockcroft gault equation
eCCR = (1.23 x (140-age) x weight) / serum creatinine
when can cockcroft gault not be used
CKD
what is the MDRD equation
eGFR = (186 x (creatinine x 0.0113) ^-1.154) x age ^-0.203
when can MDRD not be used
healthy people - it’s only for CKD
pregnant people
doesn’t take into count weight so not for young / heavy
what does the CKD-EPI equation take into account
age, sex, race, serum creatinine
give an alternative molecule to creatinine
cystatin C
why is cystatin C a good alternative to creatinine for eGFR
independent from weight / muscle mass
reflects eGFR more accurately
good for xs muscle bulk patients
name types of urine exams
urine dip
MC&S
24hr urine collection
when is 24hr urine collection used
creatinine clearance estimate
stone forming electrolytes
if the dipstick is -‘ve for blood, is haematuria excluded?
YES
what does urine dip test for
pH, specific gravity, protein, blood, leucocyte esterase, nitrites, ketones, flucose
what proteins are detected / not detected on urine dip
albumin IS
bene jones proteins are NOT