Chempath - assessment of renal function 1 Flashcards
What is the best measure of kidney function
GFR
Normal GFR? How does this change with age?
120mL/min
Decreases by 1mL a year
Define CLEARANCE
The volume of plasma that is completely cleared of a marker substance within a unit of time
What are the properties of an ideal marker substance when trying to determine GFR?
- Freely filtered
- Not bound to proteins
- Neither reabsorbed nor secreted
Gold standard measure of GFR - what is it? Why is it the gold standard?
Inulin (a fructose polymer)
Freely filtered, neutral charge, not processed by renal tubular cells
When is inulin clearance ACTUALLY used as GFR measure? and why?
Only used as a research tool,
because its concentration is hard to measure + a steady state infusion of inulin is required
What is a clinically viable measure of GFR? How is it measured exactly?
Cr-EDTA (ie radiolabelled)
A single injection is given.
Can be measured DIRECTLY (urine concentrations) or indirectly ( calculated by plasma regression curve)
Why is urea a crap marker of GFR
- 30-60% is reabsorbed by renal tubules
- Dependent on individuals’ nutrition/hepatic function/GI bleeding
What factors can alter creatinine levels?
Muscle mass
Age
Ethnicity
Sex
- Current recommendation re how to use Cr to determine estimated GFR?
- How does it differ from MDRD
Use the CKD-EPI model - adjusts for age, sex, ethnicity etc
- compared to MDRD model, it reduces the bias at higher GFRs
Alternative to serum creatinine as an estimate of GFR? What does it do? Why is it not currently used as much as Cr?
Cystatin C - a cysteine protease inhibitor
It is harder to assay
Which measure of GFR is used merely as a research tool?
Inulin clearance
Best spot urine measurement to quantify proteinuria?
Urine protein:creatinine ratio
How urine be tested in a single sample?
Dipstick
Microscopy
Protein:creatinine ratio
If the dipstick is -ve for blood, it reliably excludes haematuria. True or false?
True
