Biochemical Measurement

Question 1

What would be the ideal features of a GFR marker?

Answer 1

Appear at constant rate, be freely filtered at the glomerulus, not be reabsorbed or secreted from the renal tubule, not undergo extra renal elimination

Question 2

What are the benefits of inulin as a GFR marker?

Answer 2

Appears at constant rate, freely filtered at glomerulus, not reabsorbed or secreted from renal tubule, doesn’t undergo extra renal elimination

Question 3

What are the issues of using inulin as a GFR marker?

Answer 3

Isn’t endogenous and difficult to measure

Question 4

What are the benefits of using urea as a GFR marker?

Answer 4

Endogenous, easy to measure, freely filtered at glomerulus, not secreted from renal tubule

Question 5

What are the issues of using urea as a GFR marker?

Answer 5

Doesn’t appear at a constant rate, reabsorbed from the renal tubule, undergoes extra renal elimination

Question 6

What are the benefits of using creatine as a marker for GFR?

Answer 6

Endogenous, easy to measure, appears at constant rate, freely filtered at glomerulus, not reabsorbed from the renal tubule, doesn’t undergo extra renal elimination

Question 7

What are the issues of using creatine as a marker for GFR?

Answer 7

Its secreted into the renal tubule

Question 8

What are the confounders of creatine as a GFR marker?

Answer 8

Age, sex, muscle mass, diet

Question 9

What will frankly elevated creatine correlate with?

Answer 9

Biochemically obvious kidney disease

Question 10

How does the kidney process creatine?

Answer 10

90-95% is filtered in the kidney, 5-10% is secreted by the distal tubule

Question 11

What does clearance represent?

Answer 11

The volume of plasma that is theoretically cleared of a substance per minute

Question 12

How is urinary creatine clearance calculated?

Answer 12

Urine creatine concentration x urine volume/serum creatine concentration x duration of collection

Question 13

Can people have the same creatine concentration as each other but a different GFR?

Answer 13

Yes = two people can have the same serum concentration of creatine but a huge difference in GFR

Question 14

What is the concept that underpins GFR measurement?

Answer 14

Clearance

Question 15

What is stage 1 chronic kidney disease?

Answer 15

Kidney damage with normal or increased GFR (>=90)

Question 16

What is stage 2 chronic kidney disease?

Answer 16

Kidney damage with mild decrease in GFR (60-89)

Question 17

What is stage 3 chronic kidney disease?

Answer 17

Moderate decrease in GFR (30-59)

Question 18

What is stage 4 chronic kidney disease?

Answer 18

Severe decrease in GFR (15-29)

Question 19

What is stage 5 chronic kidney disease?

Answer 19

Kidney failure (<=15 or dialysis)

Question 20

What are the to concepts related to creatine clearance?

Answer 20

Cockcroft-Gault and 4-variable MDRD

Question 21

What are some features of Cockcroft-Gault creatine clearance measurement?

Answer 21

Incorporates age, sex and weight

Widely used to calculate drug dosages

Question 22

What are some features of 4-variable MDRD?

Answer 22

Incorporates age, sex and ethnicity

Widely used on biochemistry reports

Question 23

What is GFR a measurement of?

Answer 23

Glomerular function

Question 24

What is the validated reference standard for measuring GFR?

Answer 24

51Cr-EDTA

Question 25

What are some markers of GFR?

Answer 25

Creatine = widely used but variably useful Urinary creatine clearance = more sensitive than serum creatine but mostly historical eGFR = better than creatine, not accurate at higher GFR

Question 26

What does proteinuria provide a measure of?

Answer 26

Glomerular function

Question 27

Is protein in the urine sometimes normal?

Answer 27

Yes = plasma proteins are usually retained

Question 28

How can proteinuria be estimated?

Answer 28

By doing a 24hr collection | Protein:creatine ratio also helpful

Question 29

What does protein >150 mg/day in the urine signify?

Answer 29

Significant glomerular damage

Question 30

What is microalbuminuria?

Answer 30

Excretion of albumin in abnormal quantities but is still below the limit of protein detection by dipstick

Question 31

What is the earliest expression of diabetic nephropathy?

Answer 31

Microalbuminuria

Question 32

What is glomerular filtration useful for?

Answer 32

Efficient way to selectively rid the body of waste

Question 33

What occurs in counter-current multiplication?

Answer 33

Energy is used to generate osmotic gradient that enables water reabsorption from the tubular fluid = produces concentrated urine