6: Biochemistry of renal disease Flashcards
Why is inulin a good marker for GFR?
Freely filtered
Not reabsorbed
Not secreted
Why isn’t inulin always used as a marker for GFR?
Needs to be injected into patient
Why isn’t urea used as a marker of GFR?
Recycled in kidneys and reabsorbed in GI tract - so GFR isn’t constant
Which natural substance is used as a marker of GFR?
What’s the one caveat?
Creatinine
Small amount secreted into the tubules from capillaries, so can overestimate GFR
As GFR decreases, what happens to [creatinine] of the plasma?
Increases
As kidneys can’t filter it
At high GFRs, [creatinine]serum (is / isn’t) useful for estimating kidney function.
isn’t sensitive at high GFRs
only sensitive when GFR is low
What is clearance?
Volume of plasma cleared of a substance PER MINUTE
What two factors affect your creatinine levels?
Muscle mass
Diet
Because a biochemist can’t gauge a patient’s muscle mass and diet off of a sheet of paper, what is used to estimate their creatinine production instead?
Age
Sex
Ethnicity
What is the difference between GFR and eGFR?
eGFR modified based on age, sex and ethnicity
As these can affect creatinine production rates
Which type of creatinine clearance is more sensitive?
What estimate is better than both of them?
Urinary creatinine > Serum creatinine
eGFR
How can the degree of proteinuria be estimated?
24h urine protein collection (gold standard)
Protein/creatinine ratio (more convenient, less accurate)
Urinalysis (even more convenient, least accurate)
What excretion of protein is an indicator of severe glomerular damage?
> 150 mg/day
What is biopsied to diagnose multiple myeloma?
Bone marrow
What type of proteinuria is caused by multiple myeloma?
Which type of protein accumulates?
Overflow proteinuria
Bence-Jones protein
What type of renal syndrome is seen when the glomeruli are very leaky to proteins?
Nephrotic syndrome
What are the signs of nephrotic syndrome?
Proteinuria
Fluid retention and oedema - (pitting) oedema
Hypoalbuminaemia
Hyperlipidaemia
What is microalbuminaemia?
Proteinuria in levels undetectable by a urinalysis dipstick
Microalbuminaemia is the earliest sign of which disease in diabetics?
Nephropathy
Which drugs can slow the progression of renal disease detected early by microalbuminaemia?
ACE inhibitors
ARBs
What are some pre-renal causes of oligouria?
What is the mechanism?
Blood loss
Hypovolaemia e.g sepsis
Mechanism: decreased renal perfusion
What are some post-renal causes of oligouria?
What is the mechanism of it?
Kidney stones
Malignancy
Blockage of urine flow
What are some renal causes of oligouria?
Glomerulonephritis
Nephrotoxic substances
If urine osmolality decreases, what is dysfunctional?
Renal tubules
not hyperconcentrating urine anymore
