Dexa Confusion - Osteoporosis Message Board

PikaB · 04-27-2007, 08:58 AM

Different DEXA machines can give different results. My endo has his own DEXA machine, so when I had my annual physical from my primary care provider I also got a referral for a DEXA at the lab where I had my original DEXAs, so that I could compare them. The latest T-score results from the two different DEXA machines make no sense to me:

Machine A (tested 2/15/07)
Spine: -1.95
Hip: -1.58
These results show substantial improvement since the last time I was tested on this machine, a year earlier.

Machine B (tested 4/25/07)
Spine: -2.7
Hip: -2.3
These results show no improvement since the last time I was tested on this machine, 7 months ago.

I don't believe both machines are accurate; I don't believe my BMD could have really worsened so much in 2 months (while taking Forteo).

osteoblast · 04-27-2007, 10:51 AM

PikaB-this has really been a source of confusion to me as well. Did you compare the g/cm(sq) for each location? On my dexa results, besides the t and z score there is a bmd# which is indicated with the notation g/cm (sq). I have to say however that this did not really help me to get a handle on the situation because the numbers really varied one machine to another despite the interval between dexas being pretty close in time, as in your situation. What does your dr. have to say about the numbers?

I don't understand why it's not calibrated like a scale so the results are standard.

In the final analysis, what do you think?? Is this correct-

Machine A -two tests 12 months apart , substantial improvement. Was the first test prior to forteo?

Machine B-two tests 7 months apart,no improvement.

Could I ask what were you beginning numbers on machineA?

Location, location, location???
Personally, because of my results on three different machines I wonder if not only is machine variation an issue but also operator affected results. This questions was raised in my mind by a technician at a local clinic because she said when I come for my dexa to be sure to bring the first dexa so she could see where the machine was place for the reading and get it in the same location. My dr. ended up not sending me to that clinic for the dexa.
But I wonder about the technician's comment.Have you ever heard of this? Could there be anything to this?

PikaB · 04-27-2007, 02:00 PM

osteoblast:
These were all my T-scores, on Machine A (lab referred to by PCP) or Machine B (DEXA in endo's office):

1/7/05 (A) Spine -2.2, Hip -1.67
1/10/06 (A) Spine -2.65, Hip -2.19
2/23/06 (B) Spine -3.1, Hip -2.4
3/20/06 began Forteo
9/12/06 (B) Spine -2.5, Hip -2.3
2/15/07 (A) Spine -1.95, Hip -1.58
4/25/07 (B) Spine -2.7, Hip -2.3

I have a printout of the results from Machine A, which includes the g/cm(sq) number; however Machine B (in the endo's office) results are on his computer. I asked for the the g/cm(sq) numbers for Machine B after the first 2 tests, but I didn't ask after the last test, because I noticed that the numbers did not align with the numbers for Machine A. On the web, it says that the different models of densitometers use different conversion factors for T-scores. The two machines look like different models, but I don't know what they are.

I didn't bring the results from the test on Machine A (in Feb. 2007) to my endo, because I was afraid that if I mentioned it to him, he wouldn't want to do another DEXA so soon. I will definitely bring it to my next appointment with him, but that's three months away.

Which Machine is more accurate? Naturally I hope that Machine A is more accurate. Since it's in a lab which does lots of tests daily, their technician should be very familiar with it, and there should be routine maintenance to insure it is working properly. My endo operates Machine B himself.

osteoblast · 04-27-2007, 02:42 PM

PikaB-are you torn between elation(machineA) and dismay(machine B) and confusion(the A and B problem)?

It looks like it's really just the 4/07 spine that presents an issue in your case. While the numbers are different -the trends look ok except for the 4/07 spine on B. Unless, I am not looking at things correctly-isn't that the one? I wonder if the endo would give you a freebie re-do to see if it was just some quirk?

Also, when you have the dexa are you told not to have calcium within the prior 24 hours? First and second dexas ( second was at Mayo)-nothing said to me about calcium. Third dexa ( at a very good metropolitan hospital )they were very strict on this. I was there for another matter the day before, so I went over to the imaging clinic to see if I could get it done that day. No they said because I had calcium within past 24 hours.

I have the same sort of situation as you do - on a bit more time compressed situation and 3 machines. So I have no idea what to think! There is no legitimate (based on fact) reaction that I can rationally have. Second dexa better than first on spine and not as good on hip. Third better than first two on hip and not as good as second on spine but better than first on spine. If I just focus on hip -I feel good. If I focus on spine -not good. But the forteo should have more effect on spine???? I am also very confused! I will just will keep plugging away doing what I need to do-supplements, exercise and balance work.

I am going to take heart in studies done by researchers with forteo ,under what were controlled conditions( must be same dexa machine-wouldn't you think)and the general and significant trend was improvement. Can you think of any other way for us to look at it??

DesertBloom · 04-27-2007, 04:14 PM

Hi Pika: I would take your dexa films to your Endo and have him recalculated the scores. I was just talking to my Dr about this today, and she said that usually the discrepancies that she sees on t-scores is in the way the radiologist/technician calculated it. My Dr also has a dexa in their office, and uses a cert densitometrist, and the Dr read them; if they get a score from some other facility that is greatly different, than theirs, they recalculate and somehow factor in the differences between the models used.

I would think the better score makes more sense, given the treatment etc, and would tend to think there is a human error or equipment differentiation.

I'm in a situation where I've never had a dexa, only a qct, and we are getting ready to do the dexa knowing ahead of time that were are going to get differing scores. Since I'm under 60, the differences shouldn't be as great, qct scores drop with age, but we're going into this knowing they won't be the same, and the Dr will have to figure out the unproduceable nature of it, and hope see's accurate. At least I will know what my actual score is now, but we won't know how far the qct over/underestimated it to begin with. I hope that makes sense

I also have another prob where the original Dr

only scanned the lumbar spine twice at -3.6 & -3.4 and nothing else sooo go figure.

Good luck...