How is menopause diagnosed?

A GP (general practitioner, primary care physician) should be able to diagnose menopause or peri-menopause if he knows the age of the patient, has information about her menstrual patterns, and receives feedback from her on her symptoms.
Apart from a blood test which can measure levels of FSH (follicle-stimulating hormone), there is no definitive test to diagnose menopause or peri-menopause. FSH blood levels rise when a woman is in the menopause. However, as FSH levels tend to fluctuate a lot during the menopause and peri-menopause, the test may provide a little data, and is not that helpful for a diagnosis. Under certain circumstance a doctor may order a blood test to determine the level of estradiol (estrogen). As hypothyroidism (underactive thyroid) can cause menopause-like symptoms, a blood test to determine the woman's level of thyroid-stimulating hormone may be recommended.