Describe the relationship between creatinine clearance and serum creatinine concentrations. What are the potential pitfalls in using serum creatinine concentrations to assess renal function in a critically ill patient in ICU?

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College Answer

It was expected candidates would describe that both these are surrogate measures for
Glomerular filtration rate. Credit was given for clear definitions, formula and normal values
(such as plasma clearance is the volume of plasma cleared per unit time). It was expected
candidates could explain that serum creatinine results from a balance of creatinine produced
and excreted and hence the slow response time and limitations for its use because of changes
in both production and excretion.
Extra credit was given for appreciating the non linear relationship between changes in serum
creatinine and creatinine clearance and that significant changes in glomerular filtration can
occur before this is reflected in the serum creatinine. Comment on the problems of dilution
with acute changes in fluid balance and that tubular secretion of creatinine can occur when
the serum creatinine concentration is high both gained extra marks.
Syllabus D1 2
Reference Ganong 22nd edition 699-728