Find PageIndexChanged event in client side inside ajax "OnRequestStart"

[Covertix]

Hi,

I am using RadGrid control on my web application.
I tried to change hidden field value on server side when changing the grid page index, but the new value is not passed to the client.
I read and found out that I can recognize a page index changed inside the ajax function OnRequestStart.
How can I recognize that the trigger for the OnRequestStart function is really the grid page index change?

Thanks.