How do i know the current post type when on post.php in admin?

Im trying to do something with an admin_init hook if – and only if – the user is editing a post (post.php) with post type “event”. My problem is that, even though wordpress points to a global variable calls $post_type. if i do:

global $post_type;
var_dump($post_type);

It returns NULL.

but if I do this:

global $pagenow;
var_dump($pagenow);

it returns my current page. i.e. “post.php”.

I looked into this function $screen = get_current_screen(); but thats not declared until after the admin_init hooks has run, and then its to late.

So my question is, how do I, by the time admin_init is run, find out what post type the current post being edited is. if the url is post.php?post=81&action=edit then, how do I know what post type postid=81 is?

Thanks
Malthe