I drove 300 miles to screen for a study with them, and they didn't even call back to say why I didn't make it in. I called, and left a message with the coordinated of the study a few times, and she didn't return any calls. I know there are times when you drive a long way, and don't make it in, but it looks like the clinic could at least have the courtesy to call, and let you know why.
make a written request for your screening labs, and call back and ask to speak to the doc to find out. they don't have to tell you, but they probably will. i got in 1 think 1/3 of the times i screened there, had a couple times of being sent home at check in for false positives.