4 ms·

A 1.3% margin of error is the difference over the entire time of wearing it. It looks like on the first day, comparing blood glucose with FreeStyle Libre CGM,

• ng12 9y ago
  > Is there sufficient evidence of the benefit of CGM over fingerprick tests to believe that this caution could cause actual harm? This is a question you could only ask if you were looking only at the data without understanding the problem at hand. To answer your question: as a user I'm not sweating Zone B. That doesn't even register as a problem. Zone C is the only zone I care about, and Zone C situations can happen quite easily with fingersticks too. The entire game is imprecise -- every single day I make decisions based on incomplete data. You're going to have a very hard time convincing me that 11 hours of moderately imprecise data is more dangerous than having 11 hours of no data.
  • lambda 9y ago
    You are on HN, and likely reasonably technically inclined. You would probably pay attention to instructions that indicate that it might not be accurate during the first 12 hours of use. You would know to be a bit skeptical of readings that show hypoglycemia during that time, and might either do a fingerstick to check or just ignore it. There are many users who would not. They might make a rash decision based on that data. If the data is in Zone B a larger percentage of the time in testing, in much wider general use there will likely be cases that weren't caught in clinical trials in which it could land in Zone C. During this 12 hour calibration window, you can still use fingersticks, which you have to do for calibration purposes with other CGMs anyhow. And it likely would be a fairly minor change for them to support doubling up on sensors, so that you could overlap them in order to avoid the 12 hour window; but that change would require further testing and approval, so for now the 12 hour calibration window is left in. It was only fairly recently approved with this 12 hour calibration window, so I wouldn't be surprised if the company is working on support for pairing two sensors to one device to support doubling up like this.
    • ng12 9y ago
      > During this 12 hour calibration window, you can still use fingersticks, which you have to do for calibration purposes with other CGMs anyhow. Those aren't comparable situations. With my Dexcom I test in the early afternoon and before bed and that gives me 24 hours worth of extremely reliable information. Here's a hypothetical: let's say you test and your blood sugar is 150 mg/dl. What does that tell you? Almost nothing. Maybe your sugar was 200mg/dl 15 minutes ago and you're dropping like a rock or it was 100mg/dl 15 minutes ago and you're spiking. Maybe you've been at 150mg/dl for the last two hours. You can't really tell, so you test again in 15 minutes. Let's say it's 100mg/dl -- looks like it is dropping, unless your last reading was on the high side and this one on the low meaning nothing's really changed. So you test again in another 15m and maybe you can start putting together a picture of what's actually happening. This is a terrible process and only works if you're sitting at home doing nothing. What if you're stuck in traffic or on a crowded subway car? In a meeting at work? At the gym? On a date? In a movie theater? It can become overwhelming quickly and that's when mistakes happen. And remember this is all compounded by your body's biology: you have to think about the food you ate, how much insulin you took and when you took it, when the last time you exercised was, how much stress you're under, etc, etc, etc. And keep in mind fingersticks don't perform that much better than CGMs. They're still susceptible to error (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3317395/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3317395/) and much more susceptible to human error. Failing to wash your hands properly, not drying your hands properly, not letting the alcohol dry completely after a swab, or leaving your strips in a hot car can all cause your readings to be wildly incorrect. Another thing to note is even if your Libre is off by a huge amount (say 50mg/dl) the trend will still be accurate. Meaning if your blood sugar is constant over an hour the Libre will give you a reading that's also constant. This is extremely important because I'm much more likely to take action on trends (e.g. rising/falling blood sugars) than on individual data points. You said this in the other thread: > I would think that 12 hours of having to use a fingerstick during calibration would be preferable to twice a day fingersticks. I will tell you it is definitively not. Currently Dexcom takes two hours to calibrate and those are the longest two hours of my week. The ability to schedule those two fingersticks is much preferable to 12 hours of radio silence. > You are on HN, and likely reasonably technically inclined. Sure. I'm a "good diabetic" but that's the nature of the beast for a disease who's only treatment is constant vigilance. There's a reason why I've never gone into a hypoglycemic coma yet know people my age who are already struggling with neuropathy. The lowest common denominator here is extremely low, and if an error margin of 30mg/dl or a single false reading is going to cause you serious problems you have much greater issues with your diabetes management than your CGM.