glucometer accuracy

So I was messing around with the new glucometer and noticed I had the lancet end for arm sticks, and was wondering how inaccurate tehy are compared to finger sticks, so I gave it a whirl. 17 points higher done in the arm vs done in the finger…

Why would blood tapped from one part of a closed circulatory system not be the same as any other source?

My current glucometer, and others I have used in the past, will give a wide range of results using blood from the same stick with tests less than a minute apart. It seems to be the nature of the beast, in my experience.

IANAD - nor any other sort of expert, just got a wife with diabetes! - but I have always understood that the difference was in the movement of blood in the capillaries, the change over in the finger tips being faster than that in the arm or leg. The result being that the BG rises or falls faster in the finger tips and will be closer to that in the body’s core. To reduce this the instructions with Mrs Marcus’ meter (Abbot Freestyle Freedom Lite) suggest rubbing the area to be tested to stinulate the flow before testing.

Of course **fireman’s **point is right, the repeatability of readings from most meters is not that high!

Glucose testing on the fingers is your best bet to get a true blood reading. Testing in other spots (arms, legs), you are testing a mixture of blood & interstitial fluid.. The sugar concentration in interstitial fluid doesn’t respond as quickly to fluctuations as actual blood, so it’s not as accurate.

And also, like fireman said, the accuracy of blood glucose meters is the pits. I think they’re only required to be within 20% of the actual blood sugar as measured by a lab. Given the types of decisions that diabetics have to make based on those readings, that’s a miserable accuracy level.

Thirdly, the number one cause of fluctuations and/or misreadings I’ve found is not having clean hands. The docs tell you it’s not a big deal, but unless I’m 100% positive my hands are clean, I wash them before testing, or at the very least, use an alcohol pad to clean the area. A tiny little bit of sugar on the finger can really cause bad readings.

I once had a bit of sugar on my finger and my reading was 400 , I cleaned my finger and I got 150.

Home glucometers are to track trends. They are not expected to be as acurate as lab drawn tests.

I’ve used blood from a lab draw read 20 points higher on the glucometer than the FBS from the lab.

The ambient temperature will affect the result as will hydration and edema (swelling) if one’s hands are swollen upon arising, wait a few minutes for a more accurate reading.

This is not true for insulin dependent people.

My glucometer was marketed to me as a device to use to help determine insulin dosage for meals & corrections on a daily basis. The trends are nice to have, but you better bet I’m going to use it on a single-reading basis to determine if I’m higher or lower than ideal and either eat or give myself more insulin based on what it tells me.

That’s why it sucks that they’re so inaccurate. How many highs or lows occur because your actual blood glucose is 30 points different than what your meter tells you?

I’m afraid no one can(will) tell you that. Even the meters we used in the hospital were often different from serum glucose levels.

ah, i always test after i pee and wash my hands, warm water gets the blood to ooze out a bit faster [my body hates parting with blood… I need those capillaries to expand!]

20% sucks … I didn’t realize it was that far off.

I am currently working on a change of meds, not happy with it. I don’t seem to be able to wake up with it reading under 130-140 … and I have given it 2 weeks for my body to get accustomed to the new meds. I think the BP med is screwing it up. sigh

I hear you. I went back on birth control pills a few months ago, and I had the same issue. I didn’t even realize that’s what it was until I reached the “one week off” stage of the pill and suddenly my numbers went back to what they were pre-pill. Now that I figured out what the deal was, I can adjust, but I spent many weeks going “WTF? How come I’ve been fine for months now all of a sudden all my ratios are off?!?”

I just get frustrated … though I am very glad it is pseudogout instead of real gout otherwise my diet would be sheer hell …

To reduce the purine for gout, they recommend essentially a white bread/processed food diet. [which I do NOT have to follow thankfully. I hate white bread and overprocessed foods]

To help with diabetes they recommend a whole grain, more natural granola crunchy roughage diet.

To help with high blood pressure low sodium, low fat diet.

The diets can be mutually unworkable … but after 6 months, we have determined that sodium has no bearing at all on my bp so I can hork down the salt shaker if I like! despite my drinking water like it is going out of style, I am not retaining fluids at all, so the no sodium/diuretic shuffle is not for me. Yay, back to my old food pyramid that I love!

Now if we could just figure out a BP regimin that does not put me to sleep nor raise my glucose and keep my bp down I would be thrilled! Though the hysterectomy and loss of added hormones is great. Mood swings are a thing of the past:D

It’s not quite that bad. The +/- 20% figure is a maximum allowed error of a meter when compared to a laboratory blood serum measurement - it does not mean that your meter will vary by up to 40% from reading to reading. When Mrs Marcus first got the Freestyle Lite , I found a paper on the accuracy of the meter ( pdf link ) that showed the repeatability was significantly better than this:

I assume other meters are similar or you would hope they wouldn’t sell!

I also use a Freestyle Freedom Lite meter, I’ve never thought that it was very accurate but I think the trend is more imprtant so I make sure I do the same thing every time:
Wake up
“Take care of business”
Wash and dry my hands
Test on the inside of my Right forearm (without any extra rubbing)

Incidentally, my fasting sugar was 77 this morning (that’s the lowest reading in almost 3 years!). For the first 2 weeks of this month my fasting sugar average is running 91 right now and my average for the month of October was 93!

I have been counting calories and exercising almost daily for a couple of months now. There might be something to this diet and exercise stuff after all! (4/2007 my sugar was 312, A1C was 11.7 and I weighed 308 Pounds and now my sugar is in the low 90’s, A1C is 6.2 and I weigh ~240 Pounds).

And I eat out/frozen/prepared food almost exclusivley.


I work in a hospital and use glucometers almost daily. When a reading falls outside of certain parameters, we send a sample to the lab for verification. It is frightening how much variation there is.

And I could say the same about automatic blood pressure machines, electronic thermometers, etc.

Wow, that’s GREAT! I’m coming up on my 1 year diagnosis and have made a lot of progress as well. It’s always wonderful to wake up in the morning to good numbers.

I’m curious - do you insist on washing the test site before taking the number?