Are there instances when you prefer serum creatinine over cystatin C when estimating GFR in a patient with CKD?  

Overall serum cystatin C correlates better with measured GFR than does serum creatinine. The main block to more widespread use of cystatin C is its cost. I personally have not had an experience where the serum creatinine has been a better measure of GFR as opposed to serum cystatin C but there is da...