Count number of posts with two perso fields

Hello,

I try to count the number of posts which have two specific fields:

<?php
      $test_count = $wpdb->get_var($wpdb->prepare("SELECT COUNT(*) FROM $wpdb->posts a WHERE EXISTS (SELECT meta_id FROM $wpdb->postmeta WHERE post_id = a.ID AND meta_key = 'blablabla') AND EXISTS (SELECT meta_id FROM $wpdb->postmeta WHERE post_id = a.ID AND meta_key = 'test'", $meta_key));
      echo '' . $test_count . '';
      ?>

but nothing appears (and there is no error) :/