Blood sample size - significant?

[LittleGreyCat]

Just been through a hospital appointment.
They were very good; aware that I was diabetic and trying hard to make things easy for me.
Fortunately I am reasonably well controlled and fat adapted so fasting and gaps between meals aren't usually a problem. The question "have you brought some crisps and a sandwich for afterwards" was treated very gently.

I tested about 10:30 in the morning (fasting since previous morning, more or less) and scored a 5.1 which is nice.

Tested at the hospital at about 13:10 I scored a 6.4 on their meter.

Now my meter, a Freestyle Freedom Lite, needs virtually no blood - a sample the size of a pin head gives a result. The test strips have a tiny sample collector on each side which is very good at picking up the tiniest blood sample - apart from the usual shaking hands and short sight which makes matching the strip to the blood a challenge some times. I do like this because pain and blood are not my favourite things.

The hospital meter was very high tech, looked more like a portable Dymo labeller. The nurse was very good with the one shot lancet, and allowed me to select where and on which finger I would be stabbed, and the whole thing was painless. However the blood sample was a lot larger and I could see what looked to me like a river of blood flowing up the test strip. Which made me wonder if my BG had gone up (sheer terror etc.) or if the size of the sample might be significant.

Thinking about it, even a minor contaminant on your finger might have a significant effect on a tiny sample. If your sample is "rivers of blood" (those too young to remember Enoch Powell may miss the cultural reference) then contaminants are less likely to make a significant difference to the result.

That left me wondering if I should cross check my meter with my CareSens Dual which I have for ketone testing but which does require a larger sample.

 

[Deleted member 308541]

@LittleGreyCat, I have a Freedom Lite and as you said uses a very small amount of blood on the strip, my Accu-Chek Performa requires a bigger sample to suck onto the strip.

 

[Goonergal]

I wouldn’t have thought that the size of sample would make a big difference. So long as you’re consistent you’ll be able to spot trends - one off comparisons don’t tell you anything: how do you decide which is the more accurate of two different readings?

 

[LittleGreyCat]

I wouldn’t have thought that the size of sample would make a big difference. So long as you’re consistent you’ll be able to spot trends - one off comparisons don’t tell you anything: how do you decide which is the more accurate of two different readings?

I would perhaps trust the hospital system more, but I didn't test at the same time with my meter.

As you say, if you have two different meters and they read consistently different, how do you know which one to trust?

 

[Deleted member 308541]

As you say, if you have two different meters and they read consistently different, how do you know which one to trust?

My two Performa meters are near enough spot on when comparing them together, my Freedom Lite might be +/- 0.5 approx mmol/l different from the them. Which is good enough for me.

 

[kev-w]

I like a good drop of blood, in the past once or twice over the years when using a smaller drop I've had higher readings I didn't agree with so have tested again and used a different finger/larger drop and then got a reading more where I'd have expected, different metres, always checked with control solution bi weekly.

Neither of your readings appear to be a cause for concern mind.

 

[Bluetit1802]

Strange you should ask this because a few weeks ago I was struggling more than ever to get a decent drop of blood, but tried out the small pin heads I got - and I very definitely got lower numbers. It took me a day or so to realise it, but I have experimented and it is definite.

 

[Bluetit1802]

As you say, if you have two different meters and they read consistently different, how do you know which one to trust?

You don't! Either one of them, which is why it is advisable to stick to one, otherwise confusion reigns.

 

[ringi]

A larger drop of blood reduces the risk of a fake reading from suger etc on your hand.

 

[Antje77]

I tested about 10:30 in the morning (fasting since previous morning, more or less) and scored a 5.1 which is nice.

Tested at the hospital at about 13:10 I scored a 6.4 on their meter.

I think you'd see about the same difference if you tested at home at 10:30 and then again at 13:10. BG fluctuates, even when fasting.

 

[Bluetit1802]

A larger drop of blood reduces the risk of a fake reading from suger etc on your hand.

And yet a larger drop of blood on the same meter gives a higher reading, every time.

 

[Mr_Pot]

And yet a larger drop of blood on the same meter gives a higher reading, every time.

Maybe the difference you are finding is due in some way to the amount of interstitial fluid. How are you generating large or small drops in your experiments? I have heard of people routinely wiping away the first drop of blood and squeezing out another to test.

Incidentally, I am not sure about the larger drop of blood diluting any contaminants theory, as a larger diameter drop would cover a larger area and potentially absorb more of anything that was on your finger.

 

[Bluetit1802]

Maybe the difference you are finding is due in some way to the amount of interstitial fluid. How are you generating large or small drops in your experiments? I have heard of people routinely wiping away the first drop of blood and squeezing out another to test.

Incidentally, I am not sure about the larger drop of blood diluting any contaminants theory, as a larger diameter drop would cover a larger area and potentially absorb more of anything that was on your finger.

It could be interstitial fluid because I do have to squeeze most of the time unless the weather is very warm, and squeezing sometimes produces small drops and sometimes larger drops. I have no control over this, no matter what I do (warm water, shaking, whatever). I don't wipe away the first drop because I'd probably never get a second!

 

[ringi]

And yet a larger drop of blood on the same meter gives a higher reading, every time.

You are meant to always wipe off the first drop, and use the 2nd drop for testing - are you doing this with both the small drops and the large drops?

 

[Bluetit1802]

You are meant to always wipe off the first drop, and use the 2nd drop for testing - are you doing this with both the small drops and the large drops?

I just said I never wipe away the first drop. It is hard enough to get one drop, never mind a second. I have tried. Whatever, the small drops produce a lower reading than larger drops.

 

[ringi]

Try a larger lance.

 

[Bluetit1802]

Try a larger lance.

I use the AC Fastclix on depth 4.

 

[Mr_Pot]

You are meant to always wipe off the first drop, and use the 2nd drop for testing - are you doing this with both the small drops and the large drops?

I have heard of people doing this but not seen it written down in any official guides. I thought the main use was when you don't have access to soap and water to wash before testing.

 

[LittleGreyCat]

Most lancets come in different thicknesses.
Perhaps you need the next size up?
I know the free lancets I started with were blue plastic, and the ones on prescription were grey plastic and a thicker needle.

 

[Bluetit1802]

Most lancets come in different thicknesses.
Perhaps you need the next size up?
I know the free lancets I started with were blue plastic, and the ones on prescription were grey plastic and a thicker needle.

I use the AC Fastclix, and always have done because it is all-in-one, no physical contact with anything, and dead easy. I have it set on depth 4.