Biochemistry Flashcards
what does a low glomerular filtration indicate?
poor kidney function
what is inulin?
plant carbohydrate which ticks a lot of boxes for good marker of GFR
what makes a good marker for GFR?
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
is inulin a good marker?
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
is inulin ever used as a marker?
very occasionally when specificity is the most important (research studies etc)
what is urea?
end product of protein metabolism
benefits of urea of a marker of GFR?
endogenous
easy to measure
freely filtered at the glomerulus
not secreted into the renal tubule
drawbacks of urea?
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)
what is creatinine?
protein produced by muscle
benefits of creatinine as a marker of GFR?
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
drawback of creatinine?
small amount secreted into renal tubule
normal GFR?
> 90-120
how does creatinine relate to GFR?
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
what other factors can influence creatinine levels?
muscle mass (high muscle mass = high creatinine) diet
what proxies are used to estimate confounders of creatinine (muscle mass and diet)?
age
sex
ethnicity
estimation of GFR uses what 4 variables?
4 variable MDRM
age
sex
ethnicity
creatinine
what is urine creatinine clearance?
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
how is urinary creatinine clearance measured?
urine creatinine conc X urine volume / serum creatinine conc X duration of collection
significance of creatinine clearance in practice?
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
how is chronic kidney disease classified?
eGFR 1 = <90 2 = 60-90 3 = 30-60 4 = 15-29 5 = <15
why is proteinuria a useful measurement?
plasma proteins are normally retained so shouldn’t be any in urine
can easily estimate via 24hr collection
how much protein signifies significant glomerular damage?
> 150mg/day
urine albumin creatinine ratio?
used for diagnosis of kidney failure via spot check
high ACR indicates kidney failure
ways of expressing proteinuria?
dipstick protein - creatinine ratio albumin - creatinine ratio total protein may have different positive/negative results in same sample due to sensitivity etc
what is amultiple myeloma?
malignancy of plasma cells (B cell)
causes them to produce immunoglobulins in an uncontrolled way
causes several lytic lesions in bone
how does multiple myeloma affect protein?
production of so much immunoglobulin overwhelms the glomerular filtration resulting in overflow of protein in urine
what is overflow proteinuria?
absence of glomerular filtration meaning large proteins which are usually retained are secreted in urine
how does overflow proteinuria present?
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
what is microalbuminuria?
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)
pre-renal vs post-renal vs renal problems?
pre-renal = reduced renal perfusion post-renal = ureteric/urethral obstruction renal = intrinsic kidney tissue damage
how can you tell is the renal tubules are working or not?
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
