You get a reminder with the collector's name and a live window. They carry a sealed kit, gloves and pre-labelled vials. You confirm your name and the tests. They ask about fasting and medicines.
The draw itself is a few minutes. Pressure and a small bandage follow. Samples are barcoded before they leave the house so the tube and the order stay matched. A temperature-logged bag carries them to the lab.
If a test needs a second tube or a urine sample, they will say so before they start. You can refuse any test you did not mean to book. The amount you pay does not change their pay, so there is no reason for them to add tests at the door.
This article explains how tests are used. It is not a personal diagnosis.