Renal Clearance Flashcards
What doe kidneys do?
- maintain fluid and electrolyte homeostasis by forming urine > clear waste > recover essential solutes > eliminate acid to maintain body pH > maintain body hydration - hormone functions - metabolic functions
glomerular filtration rate (3)
- creatinine clearance
- adjusted serum creatinine
- Cystatin C
GFR formula in ml/min
[urine]/[plasma] x urine volume
how much of that mol is appearing in the urine per minute
- ideal wold = just filtered and not reabsorbed or secreted
markers of glomerular filtration
- inulin is gold standard; exogenous marker but not used in clinical labs
- creatinine (endogenous marker)
- Cystatin C (endogenous marker)
eGFR
estimated glomerular filtration rate
- GFR can be estimated to predict creatinine clearance
- serum [creatinine] without collecting 24 h urine
- Cockcroft-Gault formula
- MDRD study formula
- KD-EPI formula
Cockcroft-Gault formula
- age
- weight
- serum creatinine
- K * constant = for correcting muscle mass
- adjusts for age, weight, body surface, and sex
- still overestimates GFR by 16%
- improves accuracy for estimation of GFR in HEALTHY ppl
- less reliable with impaired renal function
MDRD study estimate of GFR
- modified diet in renal disease
- serum creatinine
- age
- gender
- a correction for race
CKD-EPI estimate of GFR
chronic kidney disease - epidemiology collaboration
- creatinine
- age
- gender
- race
- used at APL **
serum cystatin C estimate of GFR
- cystatin C
- age
- gender
** hasnt been adopted by all labs yet **
reliable enndogenous serum marker of GFR
- cystatin C
reliable endogenous serum marker of GFR
- all nucleated cel make it
- very small; doe not reappear in blood
- not detected in urine
- gives an idea of what true GFR might be
- early marker for chronic kidney disease
- ay not be reliable in absence of kidney disease if other chronic diseases present (thyroid, rheumatic, cancer)
- may be useful when creatinine measurement is not appropriate
first protein to appear in urine
- albumin (tiny-ish; and lot in blood)
- slightly bigger than tubes it has to pass through
- should NOT appear in urine!’
- pores may expand or may e damaged if stressed; so protein in urine = BAD
predictor of diabetic nephropathy
microalbuminuria
albumin in urine
first indicator of renal disease = glomerular damage
albumin excretion rate
- gives an idea of how much albumin we are losing over course of day; not just detecting it
- requires 2x24 h urine collections (not a popular test bc of this)
albumin/creatinine ratio
- [albuin]/[creatinine]; ratio!
- gives an idea of how leaky kidney is to albumin
- no need for 24 h urine
diabetes overtime consequence
chronic kidney disease = more and more leaky
more albumin in urine
is chronic disease present?
yes if glomerular permeability increased OR glomerular filtration is impaired
other markers = small MW proteins = alpha1 microglobulin, alpha2 microglobulin
assessment of tubule function
- tubular reabsorption
- tubular secretion
- tubule concentration tests (common)
tubular concentration tests
- specific gravity
- osmolality
- Fishberg Concentration Test (more about ability of tubules to concentrate)
- Fluid deprivation test (same^; water deprivation and dynamic testing)
measure of [solute] based on # of solutes present not molecular size or charge of solutes
osmolality
