You will be referred for a DEXA scan on the NHS if you have the following
Who should have a DEXA scan?
A DEXA scan may be advised if you are at increased risk of osteoporosis. Osteoporosis usually causes no symptoms at first. However, if you have osteoporosis, you have an increased risk of breaking a bone. (See separate leaflet called Osteoporosis for more details.) If a DEXA scan shows that you have osteoporosis, then you may be given advice and treatment to help strengthen your bones. Therefore, a DEXA scan may be advised if you have:
•A fracture following a minor fall or injury.
•Loss of height due to fracture of a vertebra (back bone).
•Taken steroid tablets for three months or more.
•An early menopause (aged less than 45).
•A history of periods stopping (amenorrhoea) for more than one year before the menopause.
•Other disorders associated with osteoporosis such as rheumatoid arthritis or coeliac disease.
•A family history of hip fracture on your mother's side of your family.
•A body mass index of less than 19 (that is, if you are very underweight
I think owing to costs your GP would not refer you just because you are menopausal.
A private scan can cost about £100 if you want to pay yourself.
If you diagnosed with Osteopenia it does not necessarily mean you will go on to develop osteoporosis
http://www.webmd.boots.com/osteoporosis/guide/osteopenia-early-signs-of-bone-loss