Saturday, 7 July 2012

Human Guinea Pig: Part 2 - DEXA scan

This is the second part of the story about my overnight stay in the hospital's research department, having lots of tests to look at the effect my pituitary tumour is having on my body and metabolism. You can read the first part here.

DEXA (Dual Energy X-ray Absorbtiometry) Scans - Bone Density & Body Composition

The first scan I had in the research department was a DEXA scan. People with hyperthyroidism are at risk of osteoporosis, so they wanted to check whether I had lower than expected bone density, a high risk factor. They also performed a body composition scan using the same machine, which analyses your whole body to determine what percentage of your body is made up of fat.

As the machine uses x-rays, you can't wear anything metal. They gave me a pair of scrubs to change into, as my trousers had metal bits in them. Initially, I was secretly very excited about this chance to see what I would look like as a nurse. However, the scrubs they gave me were absolutely huge - so in fact I found out what I look like as a formerly obese nurse who needs to update her wardrobe post-Weight Watchers. The trousers were so large that I could fit in one leg. Don't believe me? Here's a photo: 

Anyone care to join me in here?
I asked the lady doing the scan if I needed to remove my jewellery as well, and she said not to worry, it was just the trousers that were the problem. Seemed odd, but ok. Then I got into the scanning room and she asked me to take off my jewellery. No problem. Then I had to get lined up for the scan. Because it looks at your spine ,it's important you lie down in a perfectly straight line on the machine, which took a few minutes. Then, just as the scan was about to start, she turned around, looked at me and said "Are you wearing a bra?"

As I had not been told to take it off, I was indeed wearing a bra. It hadn't even occurred to me that the underwiring would get in the way of the scan. So I had to get up and take it off, then go through the whole aligning-your-spine-to-the-scanner process again. The DEXA scanner is basically a big table which you lie on, with an arm over the top which very ponderously slides (or rather, judders) along its length, just above you. The x-rays are fairly low dose, less than a long-distance flight. The whole process is quite quick; first the body composition scan was taken as I lay down normally, then they scanned my spine. In order to scan it properly, you have to lie with your legs up on a block so that your spine is flat against the table surface. Finally, they scan your femur at the hip joint, which requires that you rotate your leg slightly in an unnatural fashion. In order to assist with this, they tie your foot to a plastic block. It's all pretty weird.

In the corner of the scanning room was a human-sized giant egg with a little window in it. Apparently it was a BOD POD, a different kind of body composition scanner. I was pretty intigued by this piece of kit and faintly disappointed I didn't get to try it out.

The best thing about the DEXA scanner is the fact that you get an immediate print-out of your results and graphs plotting you against the expected and normal values for your age group. As it happens, I actually have slightly higher than normal bone density, rather than lower, which was good news (the blue is the normal range):

Superhuman bone density! ...or something

I was also complimented on my "beautiful" spine (actual quote - hospital folk give you very weird compliments).

Work it, baby.
However, the most interesting results were from the body composition scan. My body composition came out as 36% fat, which is at the upper end of the normal range for my age group, with the average being 30% (for women; obviously men need less fat). As you can imagine, this got me somewhat worried that I should hit the salads with a vengeance, but when I spoke to my endocrinologist the next day, she said that it was most likely due to the fact that extended period of hyperthyroidism tends to lead to muscle loss and that she didn't think I needed a lifestyle overhaul!

The me on the left needs to eat more.
Update: googling values for normal body fat percentages informs me that the American Council on Exercise considers a body fat value above 32% for women to be obese and I've found alternative readings which say anything over 35% is obese! This does nothing to make me feel better. I also found a formula used to estimate body fat based on BMI, which puts my body fat at 24.96% (full disclosure: my BMI is 20.7) i.e. a low average score, close to fitness level. Just goes to show BMI is silly and you can't rely on formulae to estimate these things!

I also worked out that, assuming I don't gain any muscle, I would need to lose 7.5 pounds in order to get down to being 30% fat. That would put my weight at 8 1/2 stone (or 54 kgs), which would put my BMI at 18.6, which would be just 0.1 away from being classed as underweight. So it seems that gaining muscle is the only solution to the problem. I can't win!

I do at least feel better about the fact that I haven't put any muscle on in my arms despite exercise, although I have put some muscle on in my stomach since the beginning of the year (bellydance, whoop!). Feels like more of an achievement now!

My DEXA scan experience:

Hassle: 3/5
Fun: 1/5
Weirdness: 3/5
Results: 4/5 (would have been 5/5, if it hadn't said I was fat!)
Total Score: 11/20

You can read the next part of the story, about my MRI scan, by clicking here.

1 comment:

  1. I think it's important to bear in mind that different sources for 'what is a healthy body fat percentage' may vary due to the method used to measure body compostion. So while the ACE might say 32% body fat is obese, that may be based on caliper measurements or hydrostsatic weighing, while DEXA scan body fat measurements often read higher, much higher in some cases. So 32% body fat may be considered obese if it's from caliper measurements, but normal if it's by DEXA scan.