Hi laszla!
A DEXA (dual energy x-ray absorptiometry) scan usually measures bone density at the lumbar spine (lower back), hip (a specific site near the hip joint), and the femoral neck (top of the thighbone or femur). The test will give you a T-score, which represents how close you are to average peak bone density.
Normal bone density: T-score is above -1.
Osteopenia (Low bone mass): T-score between -1.1 and -2.4.
Osteoporosis: T-score is -2.5 or less.
My mother had osteoporosis, so I'm at increased risk. That's one of my primary reasons for taking MHT. My BMI is 23, so it's not an added risk factor. I have not had a DEXA scan yet.
Hopefully you'll never develop osteoporosis, but FYI the FRAX tool is used to evaluate fracture risk, using bone mineral density at the femoral neck.
"The FRAX algorithms give the 10-year probability of fracture. The output is a 10-year probability of hip fracture and the 10-year probability of a major osteoporotic fracture (clinical spine, forearm, hip or shoulder fracture)."
https://www.sheffield.ac.uk/FRAX/Sounds like you're doing everything right. Your low BMI puts you at increased risk of osteoporosis, so it's great that you've had a scan. If you're able to regain the lost weight, studies indicate the odds of bone loss decrease 12% for each unit increase in BMI (approximately 5-8 lbs).
I wasn't absorbing transdermal estrogen and was switched to oral. Hopefully you'll be able to find the right MHT at the right dose for your body. Looking forward to hearing about your follow-up appointment.
If you do develop osteoporosis, an appointment with an endocrinologist may be in your future, as they are the experts who treat osteoporosis.