declare @idnum varchar(20)
set @idnum = 'set_idnum_here'

If transmittalnum is blank here:
Select TransNum From tbMedPatient Where idnum = @idnum

check phic transmittalnum here:
select SUBSTRING(TransmittalNo, 11, 10) [Phic_TransmittalNum] from tbMedElectronicClaims where IdNum = @idnum