Custom query vars available on admin pages?

I have a custom Admin Tools page that works fine. I’d like to pass a custom query param to the page handler.

function parameter_queryvars( $qvars )
{
$qvars[] = ‘cempage’;
return $qvars;
}
…
add_filter( ‘query_vars’, array( $cemeteriat_plugin,’parameter_queryvars’ ) );

But when I call https://localhost/wordpress/wp-admin//tools.php?page=cemeteriat&cempage=data_entry

cempage is not available

Help?