UDP scanning

I'm trying to scan for the accessibility of the udp ports 137 and 138
but am not sure about this. Given that udp is connectionless and doesn't
have to respond, is it even possible that I can use nmap to see if those
two ports are accessible. I know the host is up, host discovery by icmp
bounce is not what I am interested in here, just verification of whether
the udp ports are accessible through the firewall.

Thanks for any feedback.

-- 
Hari Sekhon
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