Doing creatinine clearance test is pain in the a#@?

Peeing in a bottle:) Creatinine clearance is an exact measurement of renal function, much more accurate than calculation made from serum creatinine alone. The 'pain' i guess you are referring to is that to do the test accurately requires collecting every drop of urine in a special bottle given by the lab for 24 hours. Enjoy the challenge-:).