Biochemistry

Question 1

What is the purpose of the glomerulus?

Answer 1

Filters the bad things out and keeps the good things in.

eGFR is an estimate of glomerular filtration rate.

Question 2

How can glomerular function be assessed?

Answer 2

Proteinuria.

eGFR.

Question 3

What markers can be used to measure glomerular filtration rate (GFR)?

Answer 3

Inulin (a plant carbohydrate).

Urea.

Creatinine - used to measure GFR clinically.

Question 4

What is the relationship between serum creatinine and eGFR?

Answer 4

When serum creatinine levels are low it means glomerular filtration rate (GFR) is high and within the normal limits.

When serum creatinine levels increases, GFR decreases meaning renal function is worsening.

Exponential relationship.

Question 5

What is a normal eGFR level?

Answer 5

>120mL/min.

Question 6

What are the limitations of creatinine?

Answer 6

Muscle mass - large muscle mass => increased creatinine load (high normal serum creatinine) even though GFR is normal.

Diet.

Question 7

What are the proxies for the limitations of muscle mass and diet?

Answer 7

Age.

Sex.

Ethnicity.

Question 8

What is eGFR?

Answer 8

Its an estimate of the GFR based on the patient’s creatinine, age, sex and ethnicity.

Therefore, it takes into account the GFR limitations of muscle mass and diet through the above proxies.

Question 9

What is the problem with the relationship between creatinine and GFR?

Answer 9

Creatinine isn’t sensitive to changes in GFR until the GFR is quite low.

The solution to this is that urine creatinine clearance is sensitive to changes in GFR at these higher levels of GFR (60-120mL/min).

Question 10

What is urinary creatinine clearance?

Answer 10

Question 11

What is clearance?

Answer 11

Clearance represents the volume of plasma that is theoretically cleared of a substance per minute.

Question 12

Are creatinine and urea in higher concentrations in the blood or urine?

Answer 12

Urea and creatinine are in much greater concentration within urine.

Question 13

How can you estimate plasma protein levels (proteinuria)?

Answer 13

24-hour urine collection.

Urine sample - urine/creatinine ratio.

Question 14

What protein excretion level indicates glomerular function is not effective?

Answer 14

Protein > 150mg/day.

Question 15

Table for reference only.

Answer 15

PCR = protein/creatine ratio.

ACR = albumin/creatinine ratio.

Question 16

What is overflow proteinuria?

Answer 16

Large quantities of proteins appearing in the urine (filtrate) which shouldn’t that contribute to proteinuria.
Seen in multiple myeloma and nephrotic syndrome.

Question 17

What is nephrotic syndrome?

Answer 17

Protein is lost into the urine -> less protein in blood meaning decreased oncotic pressure in the blood causing fluid to move from capillary to interstitial space leading to gross oedema.

Question 18

What is microalbuminuria?

Answer 18

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

Earliest expression of diabetic nephropathy.

Question 19

What is the treatment of microalbuminuria in a diabetic patient?

Answer 19

ACE inhibitor to slow down the progression to diabetic nephropathy.

Question 20

How can tubular function be measured?

Answer 20

Urine osmolality comparison to serum osmolality.

• If they are the same then the tubules are not reabsorbing filtrate - bad.*
• If they are very different then the tubules are reabsorbing filtrate - good.*