Ask any veteran study volunteer what they dislike most about doing research studies and chances are that most will say that being a backup is the least desirable aspect.  If you do studies long enough, you'll eventually be in a study where you are a backup.  Most people freak out when they check in and find out.  Some feel like they should have been told that over the phone.  Unfortunately, most clinics won't tell you over the phone because you might not show up which is bad for the study.

The reason that there are backups in a study is to make sure that there are enough qualified people on hand to dose.  Most clinics will re-screen your labs when you check in to make sure you are still as healthy as you were when you originally screened.  At most check ins, one or two people will fail to meet the requirements of the study and will be sent home.  Also, there is always the chance that scheduled subjects will not make it to the check in for whatever reason.

There are two types of backups, but not all studies will have both types for each study.  The 'main backup' as I like to call it, is there to replace anyone who doesn't show or or does not qualify to dose on the first dosing day.  The 'check in backup' or 'backup to the backups' is there mainly in case not everyone shows up for check in.  Not every study will have these extra backups. 

So, if you check into a study and you are a backup, don't panic!  Just because you are a backup does not mean you won't get in.  Of course your chances are a bit less.  If you are selected to be on the study, then everything is A OK.  If not, then you will likely receive some monetary compensation for the time you spent at the clinic.  This is usually outlined in the informed consent.  Depending on the clinic, you may also receive a 'priority card' for your next study which entails you to get into the study guaranteed provided all of your labs are good and you meet all study requirements.  Of course, you must meet all requirements of the current study to be eligible for the 'priority card'. 

It may not be ideal to be a backup but someone has to do it.  There are ways you can avoid being a backup, of course nothing is guaranteed.  Try to be in one of the first screenings.  If there are additional screening appointments, be sure to take the earliest dates possible.  Be on time to all of your appointments and screenings.  Tardiness can send you to the back of the line.  Also, if you have a repeat lab, this may send you to the back of the line.  It is important that if you need to do a repeat, to do it as soon as possible.  The longer you take, the longer it takes the clinic to process the labs and the study may fill up beforehand. 

With all that said, don't freak out if your a backup.  Almost every study will have them.  Also, if your study has multiple stays, there are only backups for the first check in although you still have to meet study requirements at each check in.  Who knows.  You might not get into one study but then get into a better study.  It all seems to work out in the end.