the drs can test your hormone levels and tell you if you appear to be in perimenopause, my dr tested me a couple of times. the hard part of that is that during perimenopause your levels can drop super low and spike super high, so testing is sort of hit or miss. but you would be able to tell by your physical, mood and behavior syptoms if your estrogen levels are up or down. I was diagnosed bp the same year I started having symptoms of hot flashes, night sweats and period changes (duration, frequency, degree of heaviness) at 43. My last period was at 51 but official menopause was 52. So yeah, 8 years of straight hell! Yay for menopause! I've been stable for 2 years now.