Biochem in renal

Question 1

What would the ideal marker of GFR be ?

Answer 1

• Appear at a constant rate
• Be freely filtered at the glomerulus
• Not be reabsorbed from the renal tubule
• Not be secreted by the renal tubule
• Not undergo extra-renal elimination

Question 2

What is the gold standard for measuring GFR ?

Answer 2

Inulin

Question 3

Why is inulin not regularly used in practice for measuring GFR, even though it is the gold standard?

Answer 3

Because it is not easy to measure

Question 4

What is the standard substance measure to estimate GFR ?

Answer 4

Creatinine

Question 5

What is the limitations to using creatinine to measure GFR ?

Answer 5

• Creatinine isn’t sensitive to changes in GFR until GFR is significantly reduced (GFR < 60)
• Also normal creatine levels for different people vary - as people will higher muscle mass will have a higher normal creatine and will vary with there diet

Question 6

What does clearance represent ?

Answer 6

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

Question 7

What is the reference standard for GFR measurement ?

Answer 7

Inulin clearance, ⁵¹Cr-EDTA clearance

Question 8

What are the different ways of expressing proteinuria ?

Answer 8

• PCR = protein creatinine ratio
• ACR = albumin creatinine ratio

Question 9

Protein greater than what indicated significant glomerular damage?

Answer 9

• Total protein >150mg/day
• PCR > 15

Question 10

What is the earliest sign of diabetic nephropathy ?

Answer 10

Microalbuminuria - this refers to excretion of albumin in abnormal quantities but still below the limit of protein detection by dipstick

Question 11

In terms of tubular function what must the kidneys be able to do ?

Answer 11

Must be able to reabsorb, in tubules, important substances - water, electrolytes, amino acids, glucose, etc

Question 12

What test is most useful for assessing tubular function of the kidneys ?

Answer 12

Urine osmolality - use this and compare it to serum osmolality

Take the pic for example:
Urine osmolality on day 1 higher than the serum osmolality which shows the kidneys are working as they are concentrating the urine by absorbing water but then by day 3 they are not as the serum and urine osmolality is roughly the same indicating kidney damage

Basically in result if there both there you can compare them to see if the tubules are working which can be an indicator of renal failure