Index: wp-includes/load.php
===================================================================
--- wp-includes/load.php	(revision 21685)
+++ wp-includes/load.php	(working copy)
@@ -583,8 +583,11 @@
  * @return bool True if inside WordPress administration pages.
  */
 function is_admin() {
-	if ( defined( 'WP_ADMIN' ) )
+	if ( isset( $GLOBALS['current_screen'] ) )
+		return $GLOBALS['current_screen']->is_admin;
+	elseif ( defined( 'WP_ADMIN' ) )
 		return WP_ADMIN;
+
 	return false;
 }
 
@@ -599,8 +602,11 @@
  * @return bool True if inside WordPress network administration pages.
  */
 function is_blog_admin() {
-	if ( defined( 'WP_BLOG_ADMIN' ) )
+	if ( isset( $GLOBALS['current_screen'] ) )
+		return $GLOBALS['current_screen']->is_blog;
+	elseif ( defined( 'WP_BLOG_ADMIN' ) )
 		return WP_BLOG_ADMIN;
+
 	return false;
 }
 
@@ -615,8 +621,11 @@
  * @return bool True if inside WordPress network administration pages.
  */
 function is_network_admin() {
-	if ( defined( 'WP_NETWORK_ADMIN' ) )
+	if ( isset( $GLOBALS['current_screen'] ) )
+		return $GLOBALS['current_screen']->is_network;
+	elseif ( defined( 'WP_NETWORK_ADMIN' ) )
 		return WP_NETWORK_ADMIN;
+
 	return false;
 }
 
@@ -631,8 +640,11 @@
  * @return bool True if inside WordPress user administration pages.
  */
 function is_user_admin() {
-	if ( defined( 'WP_USER_ADMIN' ) )
+	if ( isset( $GLOBALS['current_screen'] ) )
+		return $GLOBALS['current_screen']->is_user;
+	elseif ( defined( 'WP_USER_ADMIN' ) )
 		return WP_USER_ADMIN;
+
 	return false;
 }
 
Index: wp-admin/includes/screen.php
===================================================================
--- wp-admin/includes/screen.php	(revision 21685)
+++ wp-admin/includes/screen.php	(working copy)
@@ -244,8 +244,32 @@
 	public $id;
 
 	/**
+	 * Whether the screen is in the admin.
+	 *
+	 * This property is read-only. Do not write to this property.
+	 *
+	 * @since 3.5.0
+	 * @var bool
+	 * @access public
+	 */
+	public $is_admin;
+
+	/**
+	 * Whether the screen is in the blog admin.
+	 *
+	 * This property is read-only. Do not write to this property.
+	 *
+	 * @since 3.5.0
+	 * @var bool
+	 * @access public
+	 */
+	public $is_blog;
+
+	/**
 	 * Whether the screen is in the network admin.
 	 *
+	 * This property is read-only. Do not write to this property.
+	 *
 	 * @since 3.3.0
 	 * @var bool
 	 * @access public
@@ -255,6 +279,8 @@
 	/**
 	 * Whether the screen is in the user admin.
 	 *
+	 * This property is read-only. Do not write to this property.
+	 *
 	 * @since 3.3.0
 	 * @var bool
 	 * @access public
@@ -377,7 +403,7 @@
 			return $hook_name;
 
 		$post_type = $taxonomy = null;
-		$is_network = $is_user = false;
+		$is_network = $is_user = $is_blog = $is_admin = false;
 		$action = '';
 
 		if ( $hook_name )
@@ -402,10 +428,10 @@
 		if ( ! $post_type && $hook_name ) {
 			if ( '-network' == substr( $id, -8 ) ) {
 				$id = substr( $id, 0, -8 );
-				$is_network = true;
+				$is_network = $is_admin = true;
 			} elseif ( '-user' == substr( $id, -5 ) ) {
 				$id = substr( $id, 0, -5 );
-				$is_user = true;
+				$is_user = $is_admin = true;
 			}
 
 			$id = sanitize_key( $id );
@@ -419,9 +445,14 @@
 					$post_type = $maybe;
 				}
  			}
+
+			if ( ! $is_network && ! $is_user )
+				$is_blog = $is_admin = true;
 		} else {
-			$is_network = is_network_admin();
-			$is_user = is_user_admin();
+			$is_network = defined( 'WP_NETWORK_ADMIN' ) ? WP_NETWORK_ADMIN : false;
+			$is_user = defined( 'WP_USER_ADMIN' ) ? WP_USER_ADMIN : false;
+			$is_blog = defined( 'WP_BLOG_ADMIN' ) ? WP_BLOG_ADMIN : false;
+			$is_admin = defined( 'WP_ADMIN' ) ? WP_ADMIN : false;
 		}
 
 		if ( 'index' == $id )
@@ -499,6 +530,8 @@
 		$screen->taxonomy   = (string) $taxonomy;
 		$screen->is_user    = $is_user;
 		$screen->is_network = $is_network;
+		$screen->is_blog    = $is_blog;
+		$screen->is_admin   = $is_admin;
 
 		self::$_registry[ $id ] = $screen;