There are several ways.
Your monthly lab checks will tell you the creatinine level which will have stabilized to a lower level.( Remember, it will never come to normal, but should definitely come down once CAPD is started.)
Adequacy test can be performed where 24 hour PD drain fluid is collected and measured for urea and creatinine. Weekly KT/V value should be 1.7 and weekly clearance value should be at least 45 L/week.