Renal Clearance

Question 1

What doe kidneys do?

Answer 1

- 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

Question 2

glomerular filtration rate (3)

Answer 2

• creatinine clearance
• adjusted serum creatinine
• Cystatin C

Question 3

GFR formula in ml/min

Answer 3

[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

Question 4

markers of glomerular filtration

Answer 4

• inulin is gold standard; exogenous marker but not used in clinical labs
• creatinine (endogenous marker)
• Cystatin C (endogenous marker)

Question 5

eGFR

Answer 5

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

Question 6

Cockcroft-Gault formula

Answer 6

• 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

Question 7

MDRD study estimate of GFR

Answer 7

• modified diet in renal disease
• serum creatinine
• age
• gender
• a correction for race

Question 8

CKD-EPI estimate of GFR

Answer 8

chronic kidney disease - epidemiology collaboration

• creatinine
• age
• gender
• race
• • used at APL **

Question 9

serum cystatin C estimate of GFR

Answer 9

• cystatin C
• age
• gender

** hasnt been adopted by all labs yet **

Question 10

reliable enndogenous serum marker of GFR

Answer 10

• cystatin C

Question 11

reliable endogenous serum marker of GFR

Answer 11

• 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

Question 12

first protein to appear in urine

Answer 12

• 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

Question 13

predictor of diabetic nephropathy

Answer 13

microalbuminuria

Question 14

albumin in urine

Answer 14

first indicator of renal disease = glomerular damage

Question 15

albumin excretion rate

Answer 15

• 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)

Question 16

albumin/creatinine ratio

Answer 16

• [albuin]/[creatinine]; ratio!
• gives an idea of how leaky kidney is to albumin
• no need for 24 h urine

Question 17

diabetes overtime consequence

Answer 17

chronic kidney disease = more and more leaky

more albumin in urine

Question 18

is chronic disease present?

Answer 18

yes if glomerular permeability increased OR glomerular filtration is impaired

other markers = small MW proteins = alpha1 microglobulin, alpha2 microglobulin

Question 19

assessment of tubule function

Answer 19

• tubular reabsorption
• tubular secretion
• tubule concentration tests (common)

Question 20

tubular concentration tests

Answer 20

• specific gravity
• osmolality
• Fishberg Concentration Test (more about ability of tubules to concentrate)
• Fluid deprivation test (same^; water deprivation and dynamic testing)

Question 21

measure of [solute] based on # of solutes present not molecular size or charge of solutes

Answer 21

osmolality