Shipping a biological substances category B sample internationally

I need to ship a biological substances category B sample from the UK to a medical lab in the USA. The lab sent me a UPS label, the commercial invoice and a UPS Laboratory Pak.

The UPS Laboratory Pak the lab sent me, which is basically a big plastic envelope, says both "Laboratory Pak EXEMPT HUMAN OR ANIMAL SPECIMEN" and "Do not place dry ice, sharps, or materials classified as Biological Substance, Category B in this pak."

So l am confused, can I ship my sample in this Pak or not?

Also, the Pak doesn’t have a UN3373 sign on it.

So am I ok to ship the sample in this envelope or not?