As I understand it, DEXA scans cannot take into account one's height, weight, frame (large or small boned), gender, ethnicity. For example, a DEXA machnine surely cannot differentiate between, for example, a petite, small boned person of Japanese origin, a tall, large boned person of African American heritage, or a Caucasian person with either of the above mentioned examples, or anything in between.
That's why I don't trust those machines, and don't plan on having any further tests done.
Probably there'll be many who don't agree with this (or, alternatively, who do). But it's something worth thinking about.
I once thought I'd ask a DEXA technician about this, but didn't as I had already gotten a nasty look after questioning about adjustments for Strontium and didn't think the technician would welcome any more awkward questions
Have a great Memorial Day weekend
Monte
Last edited by montesflus; 05-22-2009 at 06:31 PM.
Well, if you're that worried about the inaccuracy of conventional BMD, you could try to get a vBMD (volumetric BMD) from QCT (Quantitative Computed Tomography), which can be done on a standard CT scanner. The results from vBMD might explain the differences in fracture risk between races, see http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=2663587 or other studies on vBMD.
From what I read, insurance companies and Medicare may reimburse for QCT exams with proper documentation. The CPT code for QCT bone densitometry is:
76070, CT Bone Density study
Insurance typically ranges from $125 to $150, while Medicare is typically about $110.
Four clinical indications for QCT, defined by the National Osteoporosis Foundation
1. To assess bone density of peri-menopausal women for initiation of estrogen replacement therapy.
2. To establish a diagnosis of osteoporosis or assess its severity in the context of general clinical care.
3. To monitor bone density in patients receiving glucocorticoid therapy.
4. To diagnose low bone density in patients with metabolic disorders such as mild primary hyper-parathyroidism.
The second item would seem to qualify for just about everybody.
But unless you are quite tiny, I don't think it would likely be worth the extra effort, since T-scores from a standard DEXA are already adjusted by gender and race.
Does that mean that every time a person of a different gender, race or ethnicity does a DEXA scan the machine is automatically adjusted? That would be news for me. Do you know of a specific link to this?
And no, I'm definitely ''not'' that worried about DEXA accuracy, simply because I've decided to have no more of them, since the first (and only), one I've already had. But that's just me.
I have heard about the QCT scan but am not considering doing one of those at this time either. It may very well be more accurate, I really don't know. I'm basically leery of all these types of scans and have a strange feeling that the pharmaceutical companies are somehow involved with them too.
But again. This is just me and my own personal opinion.
As mentioned on the educational site
http://courses.washington.edu/bonephys/opbmdtz.html
the bone density machines in the USA report the T-score based on race and gender.
montesflus you are right to be distrustful of the dexa machine ..even my endo doesnt trust them , her words...'dexa scan is a crude way of measuring bone density , it does not measure bone quality, at best it is merely a guideline ' and when I have my next scan she has also ordered an xray of my spine..(and that will be my last)
I too believe the dexa is a pharma companies invention and dont forget that every dexa machine is calibrated differently , thats why you have to keep going back to the same one .. it would be interesting to get scans from 3 different dexas
basically anyone with thin bones is pronounced with osteoporosis when compared to the averages in age , height , weight I dont know if ethnicity is taken into account
It's interesting that you mention about getting several scans on different machines. When I was first diagnosed I asked for a second DEXA for confirmation. By then it was a month later and I was seeing a different doctor so was tested on a different machine. You won't believe it but the T scores were almost identical. Who knows if it was an accurate of my bone strength, etc., but the tests results came back almost the same.
What bothers me most about this is that they begin the scans so late in life. Since they don't do them at age 20, 30 or even 40, how do we know that the result isn't what we've always been? I've had 3. I'm 63 years old and all 3 had the same result: -1.6. So supposedly I have osteopenia - whatever the h*ll that may be! So, who can say that I haven't always scroed -1.6? I mean, they do mammo's early on - why not these? To set a baseline? Really odd to me. I refuse to believe in osteopenia. I'm on HRT, jog regularly, do weight workouts twice a week. I may be petite but I am doing all I can do to stay strong. If my insurance wants to pay for a DEXA, so be it. But I'm not taking any of those drugs they've tried to push on me.
My endo had something interesting to say about DEXAs: she said that they do not always reflect true BMD in the case of very petite women, but they do tend to more accurately reflect fracture risk (compared to QCTs), and this is because a bone of smaller width is more likely to break even if it is of normal density. She said that QCTs are actually more accurate re BMD because they take total volume into account, but that they are less accurate at predicting fracture. She was quick to add that no test can measure bone quality and admitted that the frax prediction of a DEXA is still far from perfect.
I have recently had 2 DEXAs about 8 months apart on different machines. I was diagnosed with femoral neck/hip osteoporosis and a normal spine BMD from the first DEXA; in the second DEXA, my femoral neck BMD (g/cm2) was 28% higher, my overall hip was 20% higher, and my spine was ~10% higher. I didn't take any meds but did increase my vitaminD and calcium and I did take strontium citrate off and on for ~4 months (probably not enough to affect the DEXA, so I was told). So my first hip reading was in the osteoporosis range, while the second reading was in the (low) osteopenia range. Hmmmm....guess I'll be an optimist and go with the most recent one because it's better....
A Hologic machine is NOT recalibrated for each patient.
HOWEVER,
Patient characteristics (weight, height, gender, race, sex) ARE in your patient file.
After being analyzed, you are then compared to people of your own race, sex, etc.
As a side note to this,
A QC is run at the beginning of every day, using a spine phantom, to ensure the machine is in tolerance.
THE SOFTWARE WILL NOT ALLOW A DEXA TO BE PREFORMED WITHOUT
RUNNING THIS QC.
