Acute and Chronic Renal Failure 1 Flashcards
What is a good measure of kidney function?
Glomerular filtration rate
120ml/min normal (7.2L/hour)
Age related decline approximately 1ml/min per year
What is the association between clearance and GFR?
We can use clearance to calculate GFR. The volume of plasma that can be completely cleared of a marker substance in unit time.
If marker is not bound to serum proteins, freely filtered at the glomerulus, and not secreted/reabsorbed by tubular cells, C = GFR.
What is the equation of clearance?
C = (U x V)/P
U: Urinary conc.
P: Plasma conc.
V: Volume
What is the gold standard measurement for GFR?
Inulin clearance is gold-standard measure of GFR
5.2kD fructose polymer
Neutral charge
Freely filtered
Not processed by tubular cells
What are some endogenous markers of GFR?
Same clearance characteristics as the ideal injectable marker:
- Not plasma protein bound
- Freely filtered at glomerulus
- Not modified by tubules
What was the first endogenous marker of GFR?
Blood urea
Why was urea a good marker of GFR?
By-product of protein metabolism
Freely filtered at glomerulus
Variable (30-60%) reabsorption by tubular cells
Dependent on nutritional state, hepatic function, GI bleeding
Very limited clinical value
Why is serum creatinine useful as a marker of GFR?
Derived from muscle cells (small amount from intestinal absorption)
Freely filtered
Creatinine is actively secreted into urine by tubular cells
What are the limitations of creatinine as a marker of GFR?
Generation is not equivalent in different individuals:
- Muscularity
- Age
- Sex
- Ethnicity
What is the equation for creatinine clearance?
eCCr = (1.23 x (140-age) x weight) / serum creatinine
Adjust by 0.85 if female
What are the limitations for the equation for creatinine clearance?
Estimates creatinine clearance (not GFR)
May overestimate GFR, especially when <30ml/min
What is eGFR?
Complex equation derived from cohort studies (MDRD)
Requires age, sex, serum creatinine
What is the equation for eGFR?
eGFR = 186 x ( Creat x 0.0113) -1.154 x Age -0.203
Adjust by 0.742 if female
What are the limitations for eGFR?
May underestimate GFR if above-average weight and young
What is a clinical alternative for serum creatinine?
Cystatin C
- 13.6kD protein
- Cysteine protease inhibitor
- Constitutively produced by all nucleated cells
- Constant rate generation
- Freely filtered
- Almost completely reabsorbed and catabolised by tubular cells
