Composite cut off calculation? And to convert number to percentiles?

#1
Hi,

Can anyone please tell me how to create thresholds based on 3 parameters? For example if I have blood pressure (bp) and want to calculate BP percentiles based on height, age and gender, hope do I go about it. I have standard bp percentile cut offs.

Also can anyone tell me how to convert height to percentiles if I have height percentile cut offs?

Thank you