What's the threshold to consider a PSG abnormal enough to preclude a MSLT the following night?

To cancel the next day MSLT, I would consider cancelling or rescheduling if AHI > 10 or 15, TST < 6 hours, poor sleep efficiency (<70%), positive drug screen, staff identification of a circadian rhythm disorder we were not aware of before, etc. I have also heard of sleep docs cancelling for a low am...

We use an AHI > 14 but it is up to the referring physician to determine so if it is close, we have the tech call and confirm. We still use the AASM recommended time for the PSG of > 6 hours sleep time.