The access level is logged in users and the status is published 

Here's the code of interest:

    $blog = get_entity($guid);

    if (!elgg_instanceof($blog, 'object', 'blog')) {
        $return['content'] = elgg_echo('blog:error:post_not_found');
        return $return;
    }

Ok Thanks Cash will see how I can apply the above code to my problem. Thanks a lot for the support.