Hi there,
Try calling the DOH EMS division for a definitive answer.
Based on my experience with colleages, if your EMT expired less than a year ago, you can simply do the refresher and take the test.
If your EMT expired longer than a year, you'll need to take the entire course over again.
But, again, call the office rather than emailing...Here's the main number, (609) 292-7837