Inaccurate blood glucose readings while sick?

I know it is normal do have higher BGs when sick, but is it expected for glucometers to be less accurate when under medication or sick?

I've been using the Contour Next Link glucometer and my Dexcom G4 CGM for over a year now. I always wash my hands before testing.

This morning I woke up, washed my hands, tested and my meter said: 143.
My CGM said I was under 100, so I tested again and the meter said 101.

"No big deal," I thought, this happens sometimes... "good thing I tested again!"

At lunch I tested: 241,
tested again: 194,
one last time: 182

At this point I called Bayer and they made me check everything about my meter (including the control solution) and concluded that the meter & strips are fine, but they said "it could be the medication you are on" when I told them I got the flu yesterday and started taking meds for it.

I expect my BGs to be higher, but I didn't think that my glucometer would be inaccurate during an illness.

Has anyone ever heard of this?

Every google search I do for this ends up with a page saying how your BGs will be higher when you sick, but nothing about the meters being wrong.

Just now at dinner: 224, retested: 193.
Good thing I have a CGM as a secondary guide!

I'd try a 2nd meter if you have doubts. The CGM should be estimating/basing its numbers off your meter inputs. My experience with the Dexcom is that it's output tends to be low, and if the meter you use isn't precise (too much variability from the true BG level) then the the Dexcom estimate is even lower. I'm thinking that the CGM might have some delay when sick because blood flow is slower, but I haven't noticed the inaccuracy to shoot up.

I have to tell you, right now meters are approved for sale by the FDA if they can be accurate +/- 20%. There is no aftermarket monitoring program, so some results may be even less accurate. I have also found variations due to contamination and sometimes when getting a weird reading will carefully rewash my hand before testing.

Being sick alone can cause higher blood sugar readings. Some medications themselves can cause elevated blood sugars (for instance certain antibiotics). But it is also true that certain medications can cause false meter readings. For instance Tylenol (acetaminophen) has been known to mess up meters for quite some time.

If you are anemic (low HEMATOCRIT ) under 35% you can have trouble with some meters. I had trouble with the True Blue strips and was forced to switch to a Bayer meter after finding that my One-touch was consistently over stating my BG by +50mg/dL causing me to have low BG and my CGM would consistently understate my blood sugar Switching to a meter that compensated for my low HEMATOCRIT corrected this problem. After more than 25 years of LifeScan loyalty I was forced to change brands.........YMMV

Oops...my CGM (SG) would also overstate my BG.

The new OneTouch Verio is (relatively) stable against hematocrit. A recent paper looked at how newer meters are able to adjust against hematocrit variations. Even the best may still have as much as a +/- 10% variation.

I will have to give the Verio a try, my insurance company pays a bonus if I use LifeScan product.

One thing I have observed is that it is important to maintain a good charge in the unit. When the battery get's low, it may give bad readings just like other meters. Since it is rechargeable and has a smaller battery this is a more constant problem.