Then in that case the example I prevously posted will do the job but you will need to tell php what to place on the end of the link. Below are several more examples which will link to the same page but with an additional url parameter:
$page=basename($_SERVER['REQUEST_URI']);
$page.='&id=6438';
echo '<a href="'.$page.'">test</a>';
$page=basename($_SERVER['REQUEST_URI']);
$page.='&status=online';
echo '<a href="'.$page.'">test</a>';
And below will allow you to send the user to a different php file with the current url parameters:
$page=explode('?',basename($_SERVER['REQUEST_URI']));
$page=$page[1];
$page='filename.php?'.$page.'&id=6438';
echo '<a href="'.$page.'">test</a>';