how to find out the status of a file (checkedout, etc.) using Web Service Access

I am currently trying to check out a file on our SharePoint server using the lists class that can be found at
/sites/storage/_vti_bin/lists.asmx on any SharePoint server, as far as I know.

However, I need a function to find out the current status of a file, before actually performing a checkout. So how can I check if the file is already checked out using the Web Service Access as described here?
https://msdn.microsoft.com/en-us/library/offic/bb862916%28v=office.12%29.aspx