How likely is it to get a positive urine test 5 days before a missed period and the pregnancy be ectopic?

Unlikely ectopic: If it is positive that early, it's not likely to be ectopic. If you are at risk for an ectopic, like a previous ectopic, you should get levels checked by your GYN.

Not Linked: The two things are not linked. Last menstrual period is a guideline to determining when you became pregnant but many factors may render this inaccurate. You are at increased risk of an ectopic pregancy if you have an IUD or are pregnant after tubal ligation or if any previous surgery of pelvic infection may have scarred your tubes.