I had even less than missbonnie, I had maybe 3 questions and they were all really simple.
I have a little 3x5 card with this info on it (I made it for myself):
Sensitivity = true + / all disease
Specificity = true - / all disease
PPV = true + / all +
NPV = true - / all -
Prevalence = all disease / total
That, plus that 5% rule thingy was all I needed for those 3 questions. Honestly I'd worry a lot more about biochem 🙂
edit: oh yeah and read through the types of studies before the exam