Understanding the diagnosis

We asked the surgeon about a test for osteoporosis.  He said to ask the GP.  It looks as if, from the general reading I have done, that the bone team assume that bone density scans are initiated by GP’s and the GP’s assume that the bone team consider whether they are needed.  It is easy for a patient to slip through this assumption gap.

We asked for a scan. The GP agreed, and a couple of weeks later I was seen in a clean, calm, spacious room, and a week after that the GP had the results.  I have a vague recollection that the GP (who is really lovely and friendly), said she didn’t know what the numbers meant, but the single score prompts an osteoporosis drug and calcium and Vit D supplements if wanted (my scores on calcium and Vit D were fine but I always buy own – it seemed simpler to get the higher dose offered by prescription).

Got the pills, read all the data on the slip inside the packet, read around about side effects and effectiveness…more on that in another post.


We took a snapshot on a phone of the scores sent through by the DEXA people.   The hip scan shows that there is an increased risk of fracture (osteopenia) and the spine that there is a high risk of fracture (osteoporosis).  There are lots of numbers but you really only need to look for the summary at the bottom – WHO classification.


spine scan

hip scan

Of course, that is sufficient to decide to treat given the current guidelines, but I like to understand what is happening.  The first thing to bear in mind is that these scores are relative -they compare the amount of bone to a fit health thirty year old woman.  They tell you information about the likelihood of a fracture from a very minor fall, or, in the case of the spine, from normal activities like turning over in bed. These scores tell you how you differ from others, and I’ll write about the relative risks they indicate in another blog.

My sister sent me an excellent book called “Yoga for Osteoporosis” by Loren Fishman and Ellen Saltonstall.  The first few chapters of the book contain the best explanation of the statistical tools of Standard Deviation and T and Z scores that I’ve come across and I have three social science degrees and have spent a lot of time in statistics classes.  I’ll refer to this book several times- there’s a great section on how bones behave which I’ll write about later.

I was curious to understand the reports because I’m just generally curious, and the reading I did suggested that it was completely normal to be given a diagnosis of osteoporosis and a medical treatment without any form of explanation. Not surprising then that so many people stop taking the pills.  You get to find out about the side effects (they are described in every single packet of pills) even if you don’t experience them yourself, but you don’t know what is happening to your bones and what you might be able to do to help reduce the chances of disabling injuries. You also don’t get to know if you are improving your bones by the measures you take, unlike things like cholesterol lowering drugs where you can get almost immediate feedback on how effective you are being with lifestyle, diet and medication changes.

So, lets start with T scores.  Presuming the information in this source book (written in the USA) is the same as the UK, the T score tells you how many standard deviations your score is away from that of a healthy 25-30 year old woman.  So, that is how much you differ from someone in their prime.  The Z score tells you how many standard deviations you are away from healthy women of your age, height and weight.  We all lose bone mass from about thirty on- just some lose it a lot faster than others, and the menopause, with its change of hormone levels, makes the whole process speed up.  Men – you aren’t immune to this bone loss either, so don’t think you’re safe from fractures.  A positive score means you have denser bones than average, a negative score less dense.

So the next thing you need to know about is standard deviations – don’t worry, quick and simple explanation.  You need to know if almost everyone is about like you (say if you were an inch shorter than the average height) or if you are very different from the average ( your annual earnings if you are a top movie star).  One standard deviation around the mean includes 68.2% of people – so over two thirds of people will be in that group.  Two standard deviations include 95% of people. Only one percent of people are more than 2.5 standard deviation from the mean. If your bone density is over -2.5 standard deviations from the mean then you have osteoporosis – your bones are less dense than 99 percent of healthy young women.  Between -1 and -2.5 standard deviations from the mean indicates osteopenia – thinning bones but not yet at such a high risk of fracture.

So, peering carefully at my figures, I can see the Z and T scores for both the spine and hip.

Spine  T score    Z score

L1      -3.7            -2.8

L2      -3.0           -2

L3      -3.8           -2.8

L4     -3.9            -2.9

total  -3.6           -2.6



neck   -2.2        -1.2

total   -2.3        -1.7

The other numbers are the density readings the statistical comparison uses.  They would be meaningful to bone specialists.  I don’t need to know to figure out what the scans mean for me.

You’ll notice that the numbers in the second column are smaller than the numbers in the first column.  My bones are much less dense than those of young healthy women, and not quite so much worse than women of my age and build.  One of my lumbar vertebrae scored less than the minus 2.5 standard deviations worse than other women my age (yay!  Go lumbar vertebra 2!).  They average out to -2.6, which puts my lumbar spine in the osteoporotic range- only this area is scanned so I have no idea what the rest of my spine looks like. My lumbar vertebrae are less dense than about 99% of healthy women my age.


The hip bone is more dense- I score in the osteopenia range, where the bone has begun to thin and efforts should be made to reduce the onward thinning, but the risk of fracture is not so high. My hip bones are less dense than about 90% of healthy women my age and build.


So, why should I care what this means?  I got the pills- why not just take them and hope for the best?  Well, partly because the side effects listed are pretty gross.  Partly because compliance with the medication offered is so poor- so many people stop taking the drugs within the first two years when the risks will only get greater over the rest of their lives.  Partly because it looks as if  postural and exercise changes can make a significant difference, and partly because I’m just chronically nosy.




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