zabbix has kernel.maxfiles item to find out the limit on the open files, but no item to obtain the currently open file count.

this can be found out from the /proc/sys/fs/file-nr file - the first number is the current, the last one is the max.

zabbix currently obtains max from /proc/sys/fs/file-max reading both numbers from /proc/sys/fs/file-nr might or might not be better if both items present.