Positive urine test, negative blood test?

Jennifer
Ladies! I took a FRER 2/7/17 (picture attached) and saw a VFL. 2/10/17 I had blood work done, and it came back negative. I've also had some dark red/brown spotting since 2/10. Is it possible to get a positive urine test, and negative blood test? My doctor's nurse didn't seem too concerned, and said I should get my period soon. I bled enough to fill one tapon, and liners have been enough since. Any insight is helpful, thanks!