Describe the relationship between creatinine clearance and serum creatinine. (60% of marks) What are the limitations in using serum creatinine to assess renal function in the critically ill? (40% of marks)

[Click here to toggle visibility of the answers]

College Answer

This was a straightforward question of core CICM material. Most candidates were able to describe the Fick equation as it related to clearance, and then relate it to Glomerular Filtration Rate (GFR). Formula relating GFR to serum creatinine were often quoted incorrectly, graphs poorly constructed and/or labelled and many answers were very superficially answered. 
Better candidates were able to relate the graph to functional nephron loss and hence serum creatinine. The non-linear relationship between nephron mass (and function) and the serum creatinine was poorly appreciated by many. The nature of the variability of creatinine production with age, sex, ethnicity etc.was often omitted, as were the factors involved in the variability in an ICU patient.