Monitoring packet loss

I'd like to track the rate of packet loss for outbound packets from
some production servers.  Obviously, that's impossible.  But I think
that the rate of TCP retransmissions should be a close proxy for
packet loss.  Currently I can only observe TCP retransmissions by
using wireshark, a slow and laborious process.  But it seems to me
that the network stack should already have that information.  Would it
be possible to add a sysctl to expose the total number of
retransmissions since boot?  This information would be very useful.
It could reveal for example problems with a model of NIC, or
congestion on one network segment but not another, or a regression in
the OS.

-Alan