Work out the number of new notifications

I have an NSMutableArray of notifications, each time the view controller is opened, then NSMutableArray gets updated, how do I work out how many new items (notifications) have been added to the NSMutableArray?

NSMutableArray *arrItems;

[SharedDelegate.hnController loadDataOfType:GTUserNotifications cateId:self.strUserId curPage:curPage result:^(NSArray *results, GTControllerType type, BOOL success) {
        if (!success)
        {
            [UIView animateWithDuration:0.5
                                  delay:0.0
                                options:UIViewAnimationOptionLayoutSubviews | UIViewAnimationOptionAllowUserInteraction
                             animations:^{
                                 [self.vNoNetWork setFrame:CGRectMake(0, 430, 320, 25)];
                                 // animate here...
                             }
                             completion:^(BOOL finished){
                             }];
            //[loading stopAnimating];
            [refreshControl endRefreshing];
            return;
        }

        [self.activityIndicatorView setHidden:YES];
        [[self footerActivityIndicator] stopAnimating];
        [arrItems addObjectsFromArray:results];

        NSLog(@"ArrayItems: %@", arrItems);
        [self.tblView reloadData];

    }];

Thanks in advance