how to get form element value before submit in drupal
Once an user has logged in, the GLOBALS $user with the information related to this user is ready to use. It isn't neccesary to add an argument to the URL in your redirection.

If it isn't loaded the information you want, you could store that variable in the $user object.

function doner_user_login(&amp;$edit, $account) {
  drupal_get_form('doner_step_3');
  $GLOBALS['user']-&gt;doner_variables = $form_state['values']['about_fname'];
}