I've had to educate every lab I've ever used on how to do he proceedure. I
believe tha Lawrence has detailed instructions for how to do the test, but
this is how I have done it in the past.
I use a single pump setup and if baby is nursing both breasts at each feeding
I mix the samples. The reason I don't use a double set-up is if the mom is
loosing milk with let-down- the baby wouldn't get that milk anyway. After
combining the milk from both breasts I  gently mix the milk and take
two-three crematocrit tubes for the sample, then it's sealed (I think its
wax) and sent off to the lab asap. I ask the lab to give the results on all
the and then take the average from the samples.
Hope this helps
Marie Davis
PS: Most labs need orders from an MD for any testing
I'm not sure if time of day for sampling makes a difference