Measurement And Evaluation Of GFR

Question 1

Measuring GFR

Answer 1

amount filtered equals amount excreted

GFR = [inulin]u * V/[inulin]p

Question 2

Clinical gold standard of measuring GFR

Answer 2

Clearance of creatinine

Inc SCr = dec GFR

Question 3

Filtration factor

Answer 3

Portion of plasma that is filtered as it passes through the kidney
FF = GFR/RPF
Normally around 20%
Blood cells do not filter only water from it
Influences concentration of plasma protein in peritubular capillaries, affects reabsorption of water and solutes from proximal tubule
Typically increased in congestive heart failure (efferent constriction to maintain GFR)
Afferent dilation/constriction: little change in FF
Efferent dilation: dec FF
Efferent constriction: FF

Question 4

Blood urea nitrogen

Answer 4

Tends to increase when GFR decreases and when blood volume decreases
Increased protein catabolism can increase BUN while GFR remains normal, less useful than SCr
Increase: high protein diet, hemorrhage, trauma, glucocorticoid therapy
Decrease: low protein diet, liver disease
40-50% filtered urea passively reabsorbed mostly in proximal tubule

Question 5

BUN/SCr

Answer 5

Normal 10-20
Distinguishes pre-renal, intrinsic renal, and post-renal failure
Volume contraction with dec RBF and GFR, inc BUN and SCr, urea reabsorbed, BUN/SCr > 20
Intrarenal damage reduces reabsorption of urea, BUN/SCr < 10