When I looked at Celltrend, I think all you needed to do was to ship it to them. I believe they email/contact you to confirm payment and won't give you the results until you pay. See the check mark box "Invoice to Patient/Doctor" and quote at bottom: "For private senders: After determining your sample(s) you will receive an invoice from us. As soon as this has been settled, the results will be sent to you. "
I thought it was strange they don't demand prepayment, so maybe the samples are fairly stable or they run the tests anyway because they want the data.
Hopefully someone who has done the CellTrend test before will answer, because I too would like some clarification.
I've sent to them previously. You don't need to contact them beforehand. Check out this document from their website. You can order the tests yourself, you only need a phlebotomist to draw the blood, separate the serum and transfer it to a transport tube.
Remember to email them the tracking number after you've sent the package. They send the invoice via email after they have analyzed the sample, and after it has been paid they email you the results. An overview of the shipping rules that exists for sending blood/serum samples can be found here. I've sent packages labeled as "Exempt human specimen" successfully using FedEx. You can get a 40% discount on all shipments if you register a FedEx account. But double check if the discount is applied, because it wasn't for me at first, I had to call them to sort it out.