The technician tapped my left arm, searching for a vein. She inserted the needle. It was a dry hole. Her second attempt on the right wrist was successful, and the sample vials were filled in short order. The visit was more pleasant than average, however, with three or four tries being the norm.
Lab technicians have explained the multiple pricks and prods (and bandages) as being due to my veins being narrow and difficult to locate. I'm a wuss for admitting it, but the unpleasantness of the experience has caused me recently to forego donating blood (5-10 years ago the technicians seemed more skilled).
It's unfortunate that the blood banks aren't integrated with the labs, because I'd be perfectly willing to donate a pint once they take the relatively small amount needed for testing. After I've made the trip to the laboratory, filled out the paperwork, and incurred the discomfort of getting the flow going, the marginal cost of extracting a pint is minimal. There's probably a bureaucratic reason why blood donation and testing can't be done at the same time, but it escapes me.