Making sense of the Libre numbers – by Helen May
The Freestyle Libre will soon be made available across the NHS. I know there has been a lot of campaigning by Diabetes UK and more to make this happen. It’s great to see this kind of hard work come to fruition.
Many people will be thinking “Yay – no more finger-pricks. My finger tips can have a rest.” Unfortunately, this is not the case: the DVLA dictates any drivers still have to use their fingers; because the Libre uses interstitial fluids to calculate blood glucose (BG), there is a delay compared to fingers so in some situations when BGs are changing quickly, such as exercising, it is still useful to finger prick; and, in my experience, Flash and CGM monitoring is not as accurate as finger pricking.
But, just because we may still have to compound bruises on top of bruises on tips of fingers, that doesn’t mean a Libre is a waste of time and money. In fact, if all a Libre is being used for is to replace finger pricks, I would suggest, we are ignoring 80% of its value. It is like having a Smart Phone to make phone calls and nothing else – you may as well have a Nokia 3310 and enjoy playing snake.
With a Libre, you “flash” the sensor to get a reading. This is not the point when the sensor checks your interstitial fluids: this is the point when it downloads the last eight hours of checks to your reader (which may be an Android phone or a dedicated reader). As a result, you get much much more than one value: you get a history and, with the history, a trend. And this is where the true value comes from the Libre.
When you first get a Smart phone, to get the most out of it, you have to get your head around the apps – what do they do, how do I install them, how much power (and bandwidth) do they use, … When you get a Libre, you have to get your head around what added value it brings and how to use it. Here’s a few points, I have got my head around so far:
- What does the Libre do? It regularly checks the glucose level within interstitial fluid and stores the last eight hours of results on the sensor.
- How do I get this data? The Libre uses NFC (near field communication). If you swipe the Libre reader or a phone (with the appropriate app) with NFC enabled near the sensor it downloads the last eight hours of data to your app.
- What does the data show me? The data shows the value of the last reading, the relative direction since the last readings (is the BG rising, failing or flat). It also allows you to look at a graph to see the last eight hours of readings.
- How do I use the trend information? The trend allows you to decide what to do about the BG value. If the trend arrow shows the BG to be falling and you are about to do something which will make it fall faster (such as exercise), you may want to top up your carbs; if the trend arrow shows the BG to be rising and you about to do something which will make it rise quicker (such as go into a stressful meeting), you may want to top up your insulin. This is best decided in conjunction with knowledge of how much insulin you have in you body (IOB).
- What do I do with the graphs? The graphs alone look pretty: you could print them out and decorate your study with them. Or you could combine them with data from your exercise and food diary. (You don’t have an exercise and food diary? Me neither but learning about continuous monitoring has made me realise, it’s worth the effort, occasionally.) The graphs show you what impact certain activities and food have on your BG.
- Is there always a fast rise when eating pasta? If so, you may want to inject earlier.
- Is there a fast fall when running? If so, you may want to top up on carbs before you put your trainers on (or reduce your basal on a pump)?
- Is there a delayed rise when eating curry? If so, you may want to inject insulin later (or use a combo bolus on a pump).
- Does your BG always drop in the middle of the night? If so, you may want to think about reducing your basal dose or having a little snack before bed.
- Does your BG always rise before your weekly one-on-one meeting with your manager? If so, your manager may be stressing you out and, if you cannot work out how to manage your manager, you may want to give yourself a little insulin boost before you go in.
The true value of the data from a Libre is to make more informed decisions about your diabetes management. It’s hard work if you are doing it all the time and very difficult to see the true impact if you are always tinkering. So, I monitor and analyse for a couple of weeks, leave it to settle for a month or so and then go back and monitor for a couple of weeks.
I had a Libre trial last year and was very frustrated by it: I was expecting it to give me similar results to my finger prick and it didn’t. Since then, I have trialled a CGM and learnt more about the value of the history, graphs and trends to realise the true benefits of a Libre is not a complete finger prick replacement.
It will be interesting to find out how diabetes clinics make the decision on who to invest their Libre budget on. If I am one of the lucky ones, I will not be using my Libre reader to play snake and I will not be throwing my finger pricker away.