Med Student with Diabetes Cautions Against Unrealistic Expectations for CGMs

| May 22, 2008

Dear Editor, I am a medical student in the M.D. program at Oregon Health and Sciences University and a type 1 diabetic of almost 10 years. I use a Medtronic pump and I also use their continuous glucose monitoring system (Paradigm Real-Time).

I am writing to caution readers against developing unrealistic expectations for the current generation of continuous glucose systems (Dexcom and Paradigm Real-Time). Both of these systems are useful to establish blood sugar trend data, but they are inherently limited in several ways. I feel these drawbacks are underemphasized by companies wishing to sell extremely expensive products, and thought readers should know about a few of the not-so-desirable features before investing in these systems.

First, their readings are substantially delayed in time: i.e. they often lag as much as 20 minutes behind actual blood sugar concentration. This is because they do not sample capillary blood. Standard fingerstick monitors sample blood from capillaries, which is representative of the current blood glucose level. The sensors are detecting glucose in interstitial fluid, and the glucose concentration in this fluid may take up to 20 minutes to change in the same direction as blood glucose. Thus they cannot reliably protect against hypoglycemia, as 20 minutes of delay is entirely too long for hypoglycemia to go untreated. Exacerbating this problem is the increased inaccuracy of the sensors at both the low and high blood glucose values: Just like conventional finger-stick glucose monitors, they are less accurate at the very high and very low ranges.

Second, neither of the systems substitutes for fingerstick testing. A diabetic using these monitors must calibrate them using the same blood tests that they currently perform. The calibration must be done multiple times daily. And both companies' literature explicitly warns against using anything but a fingerstick value to make decisions about insulin doses. Diabetics thus will not be reducing the number of fingerstick tests they need to perform.

Third, the devices are very expensive to purchase and use. The initial cost of the Medtronic system is $1500 and each box of 10 sensors (which are approved for three days though many people use them for up to 7) costs $350. Even more breathtaking is that the Medtronic system is only designed to last for 12 months until the transmitter ceases to hold a charge; after 1 year of use the diabetic must pay Medtronic another $600 for a new transmitter! Thus the first year of use costs, at minimum, $1500 plus 335 days of sensors, a grand total of $5,408. To this cost, add the replacement cost of the transmitter and you reach about $6000 per year, or $16.43 per day.

This cost is not covered by most insurance plans! Only a few insurers are reimbursing this expense. All of this money is thus in addition to the regular expenses associated with having diabetes, which is costly even with adequate insurance.

Fourth, pump users will require a second subcutaneous insertion. For those with lean bodies this can be problematic, as the abdominal fat they most likely use for the pump site can become scarce when two, rather than one, insertion sites must be found. The sensor probe that resides under the skin is sensitive to being bent (unlike the insulin pump infusion set) and thus any area that is continuously flexed or that bears weight is not a great choice for the sensor probe. That means the top of the buttocks and the legs are not optimal choices for locating the sensor.

It seems to me that Diabetes Health is covering many of the positive aspects emphasized in Dexcom and Medtronic promotional information without giving the drawbacks equal time. I believe this will lead to unrealistic hopes among diabetics eagerly searching for more effective ways to manage their disease. I urge any prospective buyers of these systems to look into these issues, and many more, prior to using one of these devices (sometimes a trial can be arranged with a Diabetes Educator). While the trend data they provide is valuable, and those diabetics in need of this data will surely be able to improve their daily management, the limitations are numerous and need to be disclosed.

Sincerely,

Zachariah Kramer
OHSU M.D. Class of 2010

- - - - -

Editor's note: You can click on links to Medtronic's and Dexcom's reponses below. We appreciate the balanced discussion of this important topic.

Read DexCom's Response

Read Medtronic's Response 

Click Here To View Or Post Comments

Categories: Blood Glucose, Blood Sugar, Diabetes, Diabetes, Insulin, Insulin Pumps, Letters to the Editor, Losing weight, Low Blood Sugar, Professional Issues, Type 1 Issues


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Comments

Posted by Anonymous on 16 May 2008

A clinical article...pardon the pun.

Posted by Anonymous on 18 May 2008

Thanks for your useful perspective! There are certainly limitations with the current generation, and these are partially why attaining insurance coverage has been so difficult!

Posted by Anonymous on 18 May 2008

All of this is true. However, for once we can actually see where our blood sugars are going, instead of getting "snapshots" thru blood tests.Instead of testing with a meter and retroactively treating a high blood sugar, a diabetic can see the trend on a cgms and treat a future high in advance.

Posted by Anonymous on 19 May 2008

Although the points raised are valid, they are exaggerated just as claims to the opposite.

-We were able to reduce finger testing by 1/3 from over 12/day.
-Numerous insurance cos are covering CGMs and the number is increasing.

Finally and most importantly the letter absolutely does not mention glucose variation that is being linked to long term complications just as much as high A1c values. CGMs go a long way towards reducing undesired swings in BG.

Posted by nsherry61 on 19 May 2008

Thank you! As with many potentially useful high-tech and expensive tools, including insulin pumps and now CGMS, there seems to be a dearth of critical, real-world evaluations, especially when compared to the excitement and possitive hype generated by both corporate marketing and users refusing to be critical about a device they just spent a huge sum of money on.
I'm holding my breath for the generateion CGMS. With time, I have no doubt that CGMS will be seen as a minimum accetable standard of care. We need this.

Posted by Anonymous on 19 May 2008

Many of the points you make are very valid. However, a couple of points based on our experience using the Dexcom.

The Dexcom is substantially less expense. Currently the receiver is on sale for $450 and a months worth of sensors is $240. Not cheap ... but a lot cheaper.

Secondly the trend data can be very useful. After years of knowing that we were having low blood sugar overnight driving up morning sugars ... but not being able to figure out when, the Dexcom finally let us see that they were happening around midnight or shortly after which let us adjust insulin to avoid the worst of these episodes. Every attempt we'd made to wake up in the night to test had failed because we'd always assumed they were starting later so we almost always missed them. It also successfully warned us of lows before symptoms alerted us to them on several occassions.

Finally, I think the trend data is useful enough for making adjustments to your insulin regimen that you can get good value by using the senors only part of the time thus bringing down the cost considerably.

These are definately first generation technologies and are a far cry from what we'd like. But if you're struggling with erratic blood sugars or unexpected lows, they can be a useful tool.

We've waited a lot time for these devices and their current incarnation reminds me a lot of the first glucose testing strips. No meter. You just tried to match the color the strip turned to color swatches on the strip bottle. It was a little bit like a ouija board but it was still a thousand times better than urine testing ... and the brave souls who tried it led us to the blood glucose monitors we enjoy today.

Also

Posted by Bernfarr on 20 May 2008

Interstitial fluid measurement (according to Dr. Wolpert of Joslin) may more accurately represent the blood glucose levels in your brain. So there's some benefit to knowing this.

These are definitely 1st generation devices, but they radically improved my ability to control my blood glucose. I can 'see' the patterns for my BG after meals and during exercise. This helps me fine tune the results.

I believe most people know that CGM devices require a second insertion. In the case of the Dexcom, this isn't too painful. I hear that the Minimed needle is fairly brutal.

I think the increased control from the 1st gen devices still makes them useful. Early users need to provide LOTS of feedback to the makers so the later generations are improved.

I think that in a few years time CGMs will be seen as standard devices, like insulin pumps. But we're a long way from there right now.

Bernard

Posted by Anonymous on 21 May 2008

Check with your insurance company - the major ones are now paying for CGM devices. They are not simply not annoucing it.

Posted by Anonymous on 22 May 2008

my daughter has arthritis, and takes several pain meds that have tylenol in them. The Tylenol makes the CGM blood sugar readings go HAYWIRE!!! this is pretty scary and frustrating. she also says that the needle hurts like the dickens. (She is also a Cosmo pump user and doesn't mind that too much). We bought the CGM because we were worried about middle of the night lows... it's just easier to wake up and check her. :o(

Posted by Anonymous on 22 May 2008

The Dexcom needle is very minimal. I am in the camp of seeing trends and getting corrects before they are major. I have been a type I for 45 years. Things sure have changed from the 'tablet' tests.

Posted by Anonymous on 22 May 2008

We are the fortunate ones who luckily got insurance to cover this. HOWEVER, we were TERRIBLY disappointed that the alarms for low blood sugar are so quiet. Our main purpose was to have help at night for my daughter, and she sleeps right through her alarms. To me, they need another device that sits by the bed, the pump beams to it causing it to "alarm LOUDLY" to wake the patient up to test.

The device has helped us get more accurate A1C's. After starting the sensor, our real lows dropped drastically. Her A1C went up from 6.2 to 6.5. ..but this is more accurate for us. She treats her 70's and prevents the 40's!

Posted by Anonymous on 23 May 2008

Thanks for this valuable article. It provides a much needed counter-balance to the 'New Jerusalem' hype surrounding the current crop of CGMs. These latter assume a reactive instead of a proactive approach to Type 1 treatment.

A far cheaper and infinitely more effective way of dealing with diabetes 1 is to adopt Dr Richard Bernstein's 'law of small numbers' approach - and follow a low carb, low insulin regime with regular exercise. You can't go wrong, quite literally, because small amounts of carbs and small units of insulin do not make you 'swing' either way (up or down). Who needs CGMs when you've got normal blood sugars 24 hours a day? Think on...

Posted by Anonymous on 23 May 2008

I appreciate this perspective, but talk to those who have hypoglycemia unawareness and have suffered auto accidents or regained consciousness in an ambulance after a trip to the grocery store and you'll hear different stories.

Also, the Minimed system is not $1,500 as reported. The initial kit is $1,000 which includes the transmitter and a box of 10 sensors.

Posted by jerrysmith on 23 May 2008

I have been a MM Minilink Real Time usere since November, 2007. This system is great when it works. The major problem is consistency of results. I have found that is pretty good at detecting lows but not so great at warning of highs.

I understand the lag between the sensor and finger stick meter readings. Why can't the system give both readings: current bg and estimated bg in 15 or 20 minutes? I find myself doing this estimate in addition to looking at trend data.

The CGMS is very consistent when bg is relativetely normal and stable. I have had experience with both undetectable lows and highs. Fortunately, I still have pretty good hypo awareness. However, I have had unpleasant surprises both at very low and very high bg levels.

These products will only get better but using CGMS can be very frustrating. I agree that CGMS will become the standard of care. It would be hard to stop using CGMS, despite the limitations, if it were to become unavailable or cost prohibitive.

Posted by oakhaven on 23 May 2008

I think that Zachariah is being overly negative regarding the CGMs. As a Type 1 diabetic for 45 years undetectable hypoglycemia has been a recurrent problem leading to a required 911 call 5-6 times a year. The CGM has proven to be a godsend for me and has prevented any further 911 call. Like any piece of machinery it must be used intelligently. Of course there is a 20 minute delay between eating, for example, a glucose tablet and change in the reading from the interstitial fluid. So that would be about 10 minutes between changes in capillary blood readings and changes in interstitial readings. That would be sufficient time to warn a diabetic unless there were huge amounts of fast-acting insulin (e.g. Humalog)in the system. During nighttime there is plenty of time.

I use the Dexcom system. The probe is approved for use for one week (and you can "fake" it to make it last longer). If I had to pay for the receiver it would have been $700, not $1,500. My insurance carrier (United Health Care) supports 80% of the cost and actually saves money on 911 calls and fewer finger-sticks (5 a day rather than 10). Callibration is done twice a day and takes about a minute. I don't work in the medical field so I derive no benefit from praising the CGM systems. They're not perfect but they are extremely effective in managing hypoglycemia. If your health carrier shows resistance to supporting the cost with persistent pressure from you and your endocrinologist they will change their mind.

Posted by Anonymous on 23 May 2008

This article is excellent. I have been toying with the idea of purchasing a CGMS but have delayed because of the cost. Thank you for all posting all the other factors that are not readily disclosed. My direct reason for wanting a CGMS was to detect lows and highs. I guess I still will wait for the technology to improve. Renee

Posted by Anonymous on 23 May 2008

Thanks for your article. Sometimes patients look for convience (which I understand) but convience sometimes hinders or negatively impact quality of care.

A diabetes educator

Posted by Anonymous on 23 May 2008

I use the Medtronic System & leave my Sensor in form 12 to 20+ days. I re-charge the transmitter every 7 days. I calibrate using my pam. The readings are 7% higher than the fingers but very close to the Sensor readings making readings more accurate. Try -it!! Your transmitter has not build-up memory, don't be afraid to charge often. This info came direct from THE Sensor maven at Medtronic. I think Sensor use, no matter the cost,is the greatest thing since sliced bread. Stay Healthy!!
Diabetic for 39 years.

Posted by Anonymous on 23 May 2008

Before CGMS, 4 seizures.
After CGMS, no seizures.

Posted by Anonymous on 23 May 2008

Since I have been considering using a CGM due to nite time lows of 20-40, I am glad to hear that there is a delay time. If 20 min. is a standard, I am inclined to look into it further. Thankyou for the imput, It may have helped to save some money at this time.

Posted by kdommer on 23 May 2008

I have been on the CGMS since the beginning of this year and after only three months, my A1C was down from 7.0 to 6.6. Just having the ability to see which direction my blood sugar is trending has allowed me to make the necessary adjustments before things are out of control. And insurance is covering the bulk of my expenses. It is not perfect but it is a vast improvement over what was available to me 35 years ago when I was first diagnosed. Don't so easily rule this out!!!

Posted by Anonymous on 23 May 2008

Please beware and opened minded. Mr Kramer's article is his opinion, and has "many" inaccurate statements based on his personal opinion and not clinical facts....
First the transitter is not replaced every year. That was the old transitter...

The ability to identify blood glucose trends is truly critical in managing diabetes, it assists the person with diabetes to make informed, proactive decisions, It allows us to go beyond a "snapshot" approach. These proactive decisions can decrease the severity of lows and highs and help us to a beeter job fine tuning insulin doses.

The newer CGMS system have the ability to warn us of a "predicted high or low", thus minimizing the impact of the 20 min time delay between calillary and intersistial glucoses....

The alarms do need to louder, insurance companies do need to cover it,
But, everything can have percieved negatives, it is what we choose to do with the potential negatives, work with them or allow the negatives to hold us back.....it is you choice. Choose wisely...get the facts.
Also,Tylenol only affects the Dexcom, not the minimed sensor.

Posted by SaschiesMum on 23 May 2008

Being a type 1 for 30 years and counting, and ON a Deltec Cozmo Insulin Pump. I am one of the few that WILL NOT go for a CGMS. Plain and simple.
Zach DID point out 99% of the reasons why I will NOT go on it.
It is not because of cost. But because of the inadequecies of sites to place, the interstitial vs blood values, ect.
I learned my lesson the hard way with products like these, with the Glucowatch (original from the 90's). I am NOT going to put out thousands of dollars over a period of years, just to see the approxamation of where my sugars are or what they have been. I still would rather do my 12+ sticks per day (been known to do q1h sticks or 24x qd).
Until they either have it mainstreamed AND have it 99.999% accurate (btw, it is only accurate in 70-80% of the time currently, and that is NOT accurate enough for me) or have the accuracy increased, I will not even look into purchessing one.
Btw.. I AM hypoglycaemic UNaware. I can NOT tell my sugars are low until I have hit mid to high 30's and sometimes it is in the 20's before I realize that I am low, I also can NOT tell when I am over 250, other than test, test, test, and test some more.


SaschiesMum (not my real name but a online name)
type 1 x 30 year
OHSU Med School (M.D./MPH) class of 2001

Posted by Anonymous on 23 May 2008

I have had the MiniMed CGMS for a couple months now and I have to say it has its ups and downs. I have hypoglycemic unawareness and the pump helps me so that if it goes below a certain point (I have it at 70) then it will tell me. Same thing if it is high; it will tell me if my blood sugar is over a certain limit (I have it set at 250) so that is nice. At first, I had a huge problem with inserting the sensor needle; it has to be put in at 45 degree angle otherwise it bleeds and doesn't work. The bleeding is the worst part...but I was told by my Educator that if you do it around 60 degrees it doesn't bleed and to leave the needle in for about 5 minutes. And putting it in your side versus your stomach helps too. Also, if the sensor is not "in view" of the pump, it doesn't work. And it always seems to wake me up in the middle of the night...whether it be that my sensor is out, or there is a weak signal or something. I like all of the perks of the pump though. It tells me on the screen how much battery life is left, how much insulin I have left, and the time. So yeah it has it's plus' and minuses, but what doesn't?

Posted by Anonymous on 24 May 2008

I suspect your views will change after gaining some experience. As a diabetic on insulin for 51 years I appreciate my CGM with its imperfections. I wonder how you define hypoglycemia versus diabetic coma, and how you relate finger-stick readings to both.

Posted by Anonymous on 26 May 2008

As a former employee of Medtronic I became swept up in the hype of CGMS. I am a Diabetes Specialist and also have diabetes for the past 37 years. I have to agree with the article and would like to add that education is a vital part of managing our diabetes. Yes, the CGMS provides trend data for our blood sugars. It can assist us in making better informed decisions, however, far too often people take that information to extreme and begin to use the CGMS data solely for decision making. That WILL eventually get you into trouble!!~! I ahve seen it and experienced it myself. The data provided by the CGMS is just for extra information and to help fill in gaps that may be unexplained....that is it. I agree with another that the alarms are not loud enough so for those thinking of using for night lows...most of the time it will not wake you!!!
My best advice is use it with extreme caution!!!

Posted by Anonymous on 27 May 2008

I agree with this article almost 100%. I used the minimed system a year and a half for approximately 1 month, and had so much trouble with it that I returned it. I must say that medtronic WAS very nice to allow me to return it, and refunded the entire $1K purchase price. I did have to "eat" the cost of the sensors, as they would not accept them back, due to possible tampering liability, I guess. I had ordered several boxes, and at $35 bucks a sensor, that added up to a pretty big loss. The accuracy of the thing was always haywire, and it kept "asking" me to recalibrate it. After recalibrating it a number of times, it would automatically shut down and instruct me to insert a new $35 sensor. It would invariably go haywire in the middle of the night. The warning beep WAS too quiet, but by using it's "vibrate" function, I was able to wake up when it freaked out. Everyone always says that it's not the accuracy of the current reading that's important, but the "trends" being displayed. For me, the trend info was not particularly useful, and the current readout was ALWAYS unreliable--sometimes by as much as 30 points give or take. I don't care what anyone says--Most diabetics want a device that gives a reliable readout of the CURRENT BG value. I'll wait until that day comes before I blow that kind of money again.
Also, sensor insertion hurt like heck and I bled like crazy from the sites.

Incidentally--I think the article's info is a bit dated in regards to the unreplaceable internal battery that runs down after a year. My understanding is that the newer version device (minimed) is more compact and has a rechargeable internal battery.

Posted by AnnetteUK on 30 May 2008

I first tried the Medtronic CGMS then the Dexcom one .. I thought they are a fantastic invention.. but .. before actually purchasing one I am waiting a while longer till all the 'kinks' are out of them.
Have been on two paradigm pumps so far and honestly wouldn't want to live without it.
THAT is what really changed my life :)
Type1 51 years.

Posted by Anonymous on 31 May 2008

I have just started on the Medtronic cgm and am disappointed in the time delay as I have usually corrected a hypo before the monitor gives warning. I do like the ability to monitor trends though. I love the new paradigm, I had been using a very old pump until recently. Too bad the glucose monitor doesn't allow you to ok a bolus based on the wizards recommendations without touching the pumps key pad (sometimes pump is under clothing.)

Posted by Anonymous on 31 May 2008

Per the article, it is important to understand that CGM is not a perfect system, but I believe the advantages FAR outweigh any imperfections. Our society has to get over wanting everything to happen easily and perfectly. That is not reality! Education and lots of practice will help most in making CGM work for you. (And use the Medtronic 800# to help you learn and troubleshoot your sensor instead of wasting $35 when you try to figure it out yourself and end up killing it.)
Yes, readings are 20 minutes behind, but seeing "trending" is the key to the kingdom with CGM. Pay attention to your meter. If you aren't aware of hypo symptoms and you see a fast downward trend and it says you are at 120, do a BG to see where you really are and treat it. Also trending identifies patterns you may not have known ... My sugars are CONSISTENTLY through the roof for a few days before my period. I never knew that before. I used to just get a random high and attribute it to something else (insulin going bad ...). Also, I now see my dawn phenonemom acts up when I wake up from a nap - not just in the morning. Again, because of trending, I can see that now and can act on it. As far as the alarms, if you don't hear the alarm, it will eventually vibrate. That is what wakes me up in the middle of the night when I'm getting low.
BTW,I was one who invested in the Glucowatch and I can tell you this technology is head and shoulders more reliable than that. So folks, we ARE past the first generation of this technology. So why wait? This is pretty good and it will only get better. BTW, my A1C went from 7.9 to 6.6 in the first 3 months.
Yes, it is expensive, but you can trick the system to get more life out of your sensors. It is worth every penny. I will never go back.

Posted by Anonymous on 29 August 2008

I've been diabetic for 40 years. Up until 2 years ago, I hadn't met another Type 1 diabetic. When I finally met one at a product show, I discovered the insulin pump. This was a momentous event, and I am so happy to have a Minimed pump. Recently, because of my hypo unawareness, I decided to get a CGSM device. The first attempt to get it working was unsuccessful, and I have 3 sensors sitting in the fridge. I was going to make a second attempt this weekend (September 1), but I don't think I am going to do so, and the article by Zacharias Kramer was right on. Managing diabetes is a 24 hour chore, and having more electronics hanging from you will complicate matters further. I have reached the stage that I can be 1.7 (not sure what this is in mm), and I can still function. Not good I am sure, but I am delighted that I don't have to be carted off by the ambulance. The point about having to have another needle/canula inserted and hanging from your body is one thing, and down the road I wonder how much fat will be left on my abdomen? No, finger pricking is fine, and I don't need computer readouts and other high tech complications. It is like all high tech devices, so many options but only one or two that you constantly use.

Posted by Anonymous on 25 September 2008

I was looking at old medical journals last week and saw an interesting article , saying that cgms for heart patients "an unnecessary expense and not required) The latest gen of Heart Monitors attach to the chest wall , compress the data onto an SD Card and can be downloaded to a cardiologist - gee who thunk they could do that - New tech is always just new tech 3-4-5-6 generation later WOW

Posted by Anonymous on 21 July 2009

I am reviewing this letter to Editor almost one year after it was written. I am searching all the pro and cons of considering a cgsm. After reading the articale, reviewing the manufactures responses and the open dialog in the blog, my decision would be YES! Diabetes treatment has come a long way from dip and test days. This system has to be better. I hope that I will be a PIONEER also.

Posted by Anonymous on 19 April 2010

While I agree that I mostly use my Minimed CGM for Trending info, the cost is somewhat misstated, My CGM came with my pump at no additional cost to me at that time... that said the sensors are 10 for $350.00 as he stated and I do use mine an average of 7 days also... I'm a Union Electrician working for a utility company and am fortunate to have almost all cost covered by my medical plan. As I work with voltages of up to 220,000 volts and have become Hypo unaware My CGM has been a valuable tool to keep me safe at work.


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