Once we've discovered we have osteoporosis, we all want some reassurance that our best efforts with exercise, diet, supplements and bone medications are actually improving our bone density measurements.
The gold standard for obtaining a T-score, a calculation of bone loss, is still a DXA scan. If you've been diagnosed with osteoporosis this is the test the doctors use to determine this. However, there are some other things you can have your doctor check to see if your bone mineral density scores are getting better and not worse. Here are the most common test's used for this.
Primary Tests for Bone Loss Calculation
QCT is a quantitative computed tomography scan that gives the technician a three dimensional picture of your bones. This type of scan is often used if the patient has had surgery where titanium rods, screws or hip implants have been used to repair a fracture. Since this type of hardware is made of metal, it can make your bones look denser with a DXA scan, so some doctors may opt for a QCT instead, to get a more accurate reading.
You should have your height checked frequently, since we can lose height from fractures, additional bone loss, scoliosis, spinal disc degeneration and poor posture. It is normal to lose a certain amount of height - approximately one centimeter ever ten years after the age of 40 - but an excessive amount is not normal until you reach the age of 70. If you find you are losing more height than you should, for your age, this may be indicative of further bone mineral density loss. 
X-rays are generally used to diagnose a fracture, but an x-ray can tell the doctor if you've lost more bone, since your last DXA, if your bone loss is in the forty percent range or greater. It isn't until you've lost forty percent of your total bone that an x-ray can be a guide in determining further bone loss. 
Secondary Screening Tests for Bone Loss Calculation
- pDXA (peripheral DXA) are used in the screening stage of osteoporosis and shouldn't be relied upon in determining significant changes in bone architecture. You generally see these types of machines at health fairs, doctor's offices, at a pharmacy or store that is giving free bone density screening. Do not rely on the score obtained from this test; for an accurate bone loss measurement. They use these for screening purposes only to determine if your score warrants a DXA scan.
- QUS (quantitative ultra sound) is also used just like a pDXA at health fairs etc., for peripheral bone screening.
The lower cost portable pDXA and QUS can be done on a patients' wrist, heel, finger and other peripheral bones of the skeleton.
There are blood and urine tests you can have in-between your DXA called biochemical markers of bone. These tests tell your doctor how much bone by-product you are loosing into your blood or urine. These tests are not a substitute for a DXA, but they can provide some information on bone loss. Here's a list of all the available bone marker tests. 
Be sure to have your bone density checked as often as your doctor prescribes or as often as your insurance company allows. If you continue to have these tests, you'll have a good idea how you are doing with your osteoporosis treatment.
Medline - National Institute of Health; Aging Changes in Body Shape March 28, 2011 http://www.nlm.nih.gov/medlineplus/ency/article/003998.htm
American Academy of Orthopedic Surgeons, Osteoporosis Testing 2007 http://orthoinfo.aaos.org/topic.cfm?topic=A00413
Dr. Susan Ott, University of Washington Bone Physiology Course, Biochemical Markers of Bon January 23, 2004 http://courses.washington.edu/bonephys/opmark.html