T:slim – first impressions

It’s Thanksgiving and today I’m thankful for life-sustaining medical technology that’s also nice to look at and easy to use. My new touch screen pancreas t:slim insulin pump arrived on Tuesday and after 24 hours of patience, I ran out. So I opened the box, unwrapped my new toy durable medical equipment and began my d-life again without the hassle of dialing in carbs and BG values. It’s been a measly 18 hours since I first plugged her in (name pending) but I’ve already identified a few pros and cons about the newest member if my diabetes team. Since today’s a holiday I’m leaving this post in bullets but I assure you I’ll do my best to update this post as my experience with the t:slim evolves.

• Touch screen!!! Hello 21st century.
• Back button and Home button
• Bolus calculator – as in “I had 10+6+32+1+7g of carbs, bolus please!”
• Pretty, shines, modern, relatively small
• Copy/paste basal program – build a new basal program without having to start from scratch.
• Basal program includes ISF, I:C, and target BG
• I:C can be entered in half grams
• IOB on home screen
• 75 xtra units – see cons for explanation.
• Great history menu includes entered BGs, blouses split by type and if the calculated dose was overridden.

Cons Less awesome things:
• Touch screen less responsive than I expected
• 9 button key pad, as in three letters per button. But you only need this for naming basal programs so who really cares?
• Very slow priming and insulin delivery. Ugh!
• Only corrects for low blood sugars under 60 so I need to be a bit more conscious when dosing food with lower BGs
• Clip is a bit poorly placed on the case – only slightly north of center so the pump hangs forward while clipped to my pocket.
• Leur lock connector in awkward position and I can’t seem to hide it.
• Uses close to 50u to ready cartridge and prime 23in tube ( as opposed to about 25 for the ping) so the xtra 100 units I fill are really only and extra 75.

• Wall charger – I was directly connected to the grid for about 10 min this morning
• Multiple confirmation screens before bolus initiates.

And that’s all I got for now.


Shapeways 3-D Printed “Brixometer” Dexcom Cover

After having (and wearing out) a couple of silicon sleeves I adapted to cover my Dexcom G4 receiver, I started looking for another, even sturdier option.  Eventually I stumbled across a TuD convo about 3-D printed Dexcom covers.  For under $15 (plus shipping) I now have this form fitting hard plastic cover that was 3-D printed just for me.  (Well, it’s made to order so that’s kind of like it was made for me, right?)

Dexcom Cover

It fits my receiver like a glove, has a slightly textured surface giving it a pretty good grip, and is open on the end to allow easy access to the charging port. (Or, if your sliding charger port cover has fallen off like mine has, you can simply turn this case around and it will fit in the other direction and cover the port when it’s not in use.) Plus it has this nice pattern of holes intended to lighten it and add grip which also give it a nice black and white polka dot look (that I kind of love).

Dexcom cover

As of now, I haven’t had it long enough to comment on durability but I’m feeling pretty good about it so far – the girl who originally posted about it on TuD claims she’s had hers for a few months and it’s holding up well.

To get your own, follow this link to the listing on the Shapeways website.  I bought the “White Strong & Flexible” variety but it can also be purchased in a few other colors and a slightly smoother texture as well.


The impact of 20%

There’s been a lot of discussion in the DOC about BG test strips.  There’s the strip safely campaign focused on making sure all test strips for sale in the US are subjected to the same rigorous quality control measures to ensure optimal accuracy; many discussions over whether or not 20% error allowed by the FDA is good enough, and countless user experiences.

So, from where does this problem stem? And how big of a problem is it really?  The FDA has imposed an ISO standard on glucose monitoring. The standard is this:

ISO 15197 specifies that

> or =95% of the BG results shall fall within +/-15 mg/dL of the reference method at BG concentrations <75 mg/dL and within +/-20% at BG concentrations > or =75 mg/dL

This means that for BGs less than 75 mg/dL, our meters spit out results that are up to 15% off from reality 95% of the time, and when our BGs are over 75, they can be up to 20% off from reality.  Compliance to this standard is often shown via a Clarke error grid, like the one below (for freestyle test strips).

Clarke error grid for Freestyle Lite test strips. From http://www.diabeticnerd.com

As you’ll notice in the picture, the black dots are all within the region labeled A which is the 15-20% bracket.  You’ll also notice that while the 20% range seems huge for larger BG values, this window is actually quite small for lower BG values.  Also, for any given plasma glucose value, there is a normal distribution of BG values from 0% (completely accurate) to ±20% (with up to 5% of numbers being more than 20% inaccurate). I think it helps to visualize wha this really means by looking at this generic normal distribution:

Normal Distribution: For our purposes, imagine the horizontal axis labeled with -20% on the left where it says “-2σ” and +20% in place of “2σ” on the right. The height of the peak (centered at 0%, “µ”) is determined by the number of BG values that are of by a given percentage.  Notice that 68.2% of your BG values will be in that dark blue region with errors far less than 20%.

Imagine that you kept a running list of the error of every one of your BG meter readings compared to your real plasma blood glucose.  Then you graphed this data with the %error on the horizontal axis and the number of reading per % error on the vertical axis, you’d see a distribution very much like the one in the picture.  Replace the “2σ” and “-2σ” with +20% and -20% and the “µ” with 0% on the horizontal. (I haven’t yet found reliable data to label the y axis with, but it would likely vary from brand to brand and I think it might be reported on that little piece of paper we always throw away when we open a new box of strips.) The light blue tail regions represent the 5% of numbers that are outside of the 15-20% BG allowance and the other 95% are in the two darker blue regions with most being concentrated nearer to the middle which represents your actual BG level.

With that in mind, let’s now consider what effect the FDA regulation has in practice. What I’m really interested in is how this error translates to errors in my diabetes regimen and the impact on my BG/A1C.   Below, I’ll walk you through my calculation of insulin doses delivered based on meter reading and the resulting corrected BGs.  To simplify, I calculated using a 20% error for all BG values from 40-400 mg/dL with a target range of 70-120 mg/dL.

Fisrt, let’s look at the range of meter readings you might expect compared to your real BG.  Keep in mind that these lines contain 95% of all readings, with at least 68% of those readings concentrated closer to the dotted line than either solid line.

Meter Readings 20% accuracy

For every real BG value, your meter is calibrated to correctly identify that value with up to a 20% error. On the horizontal X axis are the real values and the green and red lines indicate the possible range of values returned by your meter.

Using my insulin sensitivity factor, I then calculated the dose of insulin my pump would deliver in response to the meter readings shown above.  Again, remember that numbers are concentrated more closely to the dotted line than either solid line.

Insulin Dose

The error in the meter readings translate to an error in correction dosing. The dashed line shows how much insulin is needed to correct a given BG value to the nearest target (omitting insulin to reach the bottom of the range or dossing to drop to the top of the range). The red and blue lines correspond to correcting a meter value that is 20% above or 20% below the actual value.

Assuming no other influences (ie spherical diabetes in a vacuum), the next graph shows how my BG will respond to getting either the min or max insulin correction.  These represent REAL BG values resulting from inaccurately dosed corrections caused by the 20% error in meter readings. The space between the lines contains 95% of all possible outcomes.

Corrected BG

The range of correction doses lead to a range of corrected BG values. The largest discrepancies occurring alongside the largest real BG values.

And lastly, I converted the above graph into percentages (because I like them).  You’ll see the maximum percent over the target range (red, from under correcting a high or over correcting a low) and under the target range (orange, from over correcting a high or under correcting a low).  This isn’t the % of resulting BG values outside of the range, just the % off from the target of a single BG resulting from inaccuracy in meter readings.  And again, the space between the lines contains 95% of all possible outcomes.

The % above or below the target range of the corrected BG.

The % above or below the target range of the corrected BG.

I’m going to say it one more time because I think it is very important.  These pictures represent the extremes – 95% of BG values are 20% accurate or better, with 68% of the values concentrated closer to reality.  This then means that all of my calculations represent ranges of data with a similar distribution.

So, there it is.  In pictures. The direct impact of the 20% FDA-approved error on our BG values (in a vacuum).

And now for my opinion on the subject: Personally, I feel like it’s just not that big of a deal.  Since I am more likely to treat a low with a standard regimen of 15-30g of carbs and protein, the under correction there is mostly irrelevant.The possibility of over or under correcting a high over 240 is very real but since I’m already in the habit of double checking higher numbers (making sure there’s no rogue sugar on my finger tips) I don’t see that as a huge problem either.  Plus the introduction of a second BG reading is enough to assure me that I’m comfortably in the 68% of readings that are far less than 20% off and not on the outskirts.

Here’s a copy of the excel sheet I used to generate these pictures.  Have fun  if you like that sort of thing and please let me know if you disagree with any of my calculations (or my opinion).

Here are a few other articles and opinions on the 20% issue:

About meters being outside of the FDA limits

Opinion and lots of facts about the FDA and meter accuracy

What the FDA regulations mean to diabetics – blog

Switching to the t:slim

http://www.tandemdiabetes.com/Products/t-slim-Insulin-Pump/It’s been nearly 9 months since I last posted anything on this blog.  Either this post will the turning over of a new leaf or maybe I’ll neglect the blog for another 9 months.  Only time will tell.

Until then, I’m here to tell the world that I’m making the change over to Tandem and should receive my new t:slim within a couple weeks.  I’ve been using an Aimas pump for nearly 12 years.  I stated on their IR1000 model (a brick with a cord), switched to the IR1250 (for the carbsmart calculator and the free iPod mini that came with it), then my beloved Ping.  As far as I’ve always been concerned, no other brand was even worth looking at – Animas is and always has been fully water proof (I’ve worn it under waterfalls, and in lakes and pools), has easy (enough) to navigate menus, and great customer service. (Although it was better back in the day when everyone else was on minimed and I was Animas’ only customer.  Not really, but that’s how it often seemed.)  I remember fighting my doctor to subscribe Animas over minimed.  I knew it was the pump for me and I couldn’t be convinced otherwise.  And to this day I have always had great experiences with my Animas pumps.

Then one day there was Tandem.  The t:slim is smaller, holds more insulin, is rechargeable (no more expensive lithium batteries insurance would never pay for), has a touch screen which allows carbs and BGs and boluses to be typed in instead of dialed, and the ever ellusive back button.  I was instantly twitterpated; it’s like Tandem knew all the things I wanted out of a pump and poof there it was!

Yet I remained reluctant.   Tandem does not offer pump trials; the t:slim is not water proof (merely water resistant); and perhaps most importantly is a start up company just breaking into the market with a first generation product.

And then my Ping’s warranty expired.   Do I sign up for 4 more years of Animas or do I take a risk and give this new company a try?  They have a 30 day return policy (from start-up day) and the only way they make to the next generation is by having customers willing to give them a chance.  Plus they’re teamed up with both Dexcom (integration, please!) and the dual-chamber-bihormonal-closed-loop-pump people at Mass General so they have a bright looking future.

I got word of my approval today and I’m pumped (excuse the pun).  Let’s hope it’s worth the gamble.

Dexcom Skin, sort of

After stumbling upon this thread at TuDiabetes, I went ahead and purchased an Insignia Pilot silicon case for my new G4 Dex.  The dimensions of each are pretty similar (Dex G4 = 101.6 x 45.72 x 12.7 mm, Insignia = 100.0 x 49.20 x 11.1 mm) and each has a rectangular screen with circular controls.  I held the G4 receiver up to the screen to visually compare, and I figured the circles wouldn’t line up perfectly, but it looked like they’d be pretty damn close.   (I’d also like to note that I ordered this one specifically, and it came with a second case in black, pictured, and a removable belt clip and arm band all for only $4.87!)

Dexcom G4 in Insignia Pilot case

Close, but not good enough!

As you can see in he photo, the alignment is somewhat worse tan I had hoped for.  I lived with it this way for about a week, and then this happened:

Dexcom G$ receiver in modified Insignia Pilot case

Take that!

The result is a somewhat wonky solution that adds traction to the receiver so it stays firmly planted in my jeans pocket, and cushions it a bit when it does manage to fall.  Since the case is made for an entirely different device, and I’ve cropped out a bit of the structure, the receiver is very easily removed, but that doesn’t really bother me.  Plus there’s the added bonus of a conveniently located window perfectly framing the charging port.

Dexcom G4 receiver in Insignia Pilot case

Another happy coincidence.

I’m still hoping Dexcom will get there act together and sell a snugly fitting case designed just for this receiver.  But until then, this may be the perfect solution.