Biochemistry

Question 1

what does a low glomerular filtration indicate?

Answer 1

poor kidney function

Question 2

what is inulin?

Answer 2

plant carbohydrate which ticks a lot of boxes for good marker of GFR

Question 3

what makes a good marker for GFR?

Answer 3

appears at a constant rate
freely filtered at glomerulus
not reabsorbed from the renal tubule
not secreted by renal tubule
doesn't undergo extra-renal elimination

Question 4

is inulin a good marker?

Answer 4

no
very impractical to try and measure
not endogenous to the body so would have to be injected into someone and watch it be excreted

Question 5

is inulin ever used as a marker?

Answer 5

very occasionally when specificity is the most important (research studies etc)

Question 6

what is urea?

Answer 6

end product of protein metabolism

Question 7

benefits of urea of a marker of GFR?

Answer 7

endogenous
easy to measure
freely filtered at the glomerulus
not secreted into the renal tubule

Question 8

drawbacks of urea?

Answer 8

doesn’t appear at a constant rate (depends on diet - i.e meat causes increase)
absorbed from the renal tubule
undergoes extra-renal elimination (1/4 goes back into the gut after the urea cycle in the liver - most still goes to the kidneys)

Question 9

what is creatinine?

Answer 9

protein produced by muscle

Question 10

benefits of creatinine as a marker of GFR?

Answer 10

endogenous
easy to measure
appears at a constant rate
freely filtered at the glomerulus
not reabsorbed from the renal tubule
doesn't undergo extra-renal elimination

Question 11

drawback of creatinine?

Answer 11

small amount secreted into renal tubule

Question 12

normal GFR?

Answer 12

> 90-120

Question 13

how does creatinine relate to GFR?

Answer 13

lower GFR = higher creatinine
exponential relationship - creatinine rises at a higher rate the lower the GFR is
- i.e creatinine isn’t sensitive to changes in GFR until GFR is quite low

Question 14

what other factors can influence creatinine levels?

Answer 14

muscle mass (high muscle mass = high creatinine)
diet

Question 15

what proxies are used to estimate confounders of creatinine (muscle mass and diet)?

Answer 15

age
sex
ethnicity

Question 16

estimation of GFR uses what 4 variables?

4 variable MDRM

Answer 16

age
sex
ethnicity
creatinine

Question 17

what is urine creatinine clearance?

Answer 17

solution to the problem with creatinine not being sensitive to changes in GFR until its very low
this is sensitive to changes in GFR at higher levels (60-120)
represents volume of plasma that is theoretically cleared of a substance per minute

Question 18

how is urinary creatinine clearance measured?

Answer 18

urine creatinine conc X urine volume / serum creatinine conc X duration of collection

Question 19

significance of creatinine clearance in practice?

Answer 19

same serum creatinine conc in two people can produce very different creatinine clearance rates
therefore can tell whether a high creatinine is due to confounders (e.g high muscle mass) or kidney disease

Question 20

how is chronic kidney disease classified?

Answer 20

eGFR
1 = <90
2 = 60-90
3 = 30-60
4 = 15-29
5 = <15

Question 21

why is proteinuria a useful measurement?

Answer 21

plasma proteins are normally retained so shouldn’t be any in urine
can easily estimate via 24hr collection

Question 22

how much protein signifies significant glomerular damage?

Answer 22

> 150mg/day

Question 23

urine albumin creatinine ratio?

Answer 23

used for diagnosis of kidney failure via spot check

high ACR indicates kidney failure

Question 24

ways of expressing proteinuria?

Answer 24

dipstick
protein - creatinine ratio
albumin - creatinine ratio
total protein
may have different positive/negative results in same sample due to sensitivity etc

Question 25

what is amultiple myeloma?

Answer 25

malignancy of plasma cells (B cell)
causes them to produce immunoglobulins in an uncontrolled way
causes several lytic lesions in bone

Question 26

how does multiple myeloma affect protein?

Answer 26

production of so much immunoglobulin overwhelms the glomerular filtration resulting in overflow of protein in urine

Question 27

what is overflow proteinuria?

Answer 27

absence of glomerular filtration meaning large proteins which are usually retained are secreted in urine

Question 28

how does overflow proteinuria present?

Answer 28

nephrotic syndrome
loss of protein from the blood causes a reduction in oncotic pressure at the level of capillaries causing loss of fluid from the capillaries into the tissue causing oedema

Question 29

what is microalbuminuria?

Answer 29

excretion of albumin in abnormal quantities but still below the limit of protein detection in dipstick
earliest expression of diabetic nephropathy
detection allows treatment to reduce risk of progression (ACE inhibitors)

Question 30

pre-renal vs post-renal vs renal problems?

Answer 30

pre-renal = reduced renal perfusion
post-renal = ureteric/urethral obstruction
renal = intrinsic kidney tissue damage

Question 31

how can you tell is the renal tubules are working or not?

Answer 31

urine osmolality compared with serum

urine should be significantly higher - if they are around the same or urine is lower, then tubules aren’t working