Absolute earliest i can take a pregnancy test for suspected miscarriage?

Patient: Hi,I suspect I may have had a miscarriage today (14/05/14). I’m only around 2 weeks pregnant.When is the absolute earliest I can take a pregnancy test? My doctor briefly mentioned taking one this friday (16/05/14) is this to soon?

Symptoms: Painful cramps, What looked like a heavy period lasting about 3 hours
lower back pain