Why is overnight fasting necessary for a blood test?

Bluetit1802 said:

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Blimey. I wish I hadn't asked now! Thank you Brunneria and Spiker. I can't imagine how horrible it must be. I know Type 1's carry glucose round with them wherever they go. Do you think Type 2's should also do this, whether on meds or not?

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Bless you. Remember, we both described 'bad ones'. I nip most of mine in the bud at a very early stage.

In my case, the best prevention is not to eat carbs - and that includes emergency glucose.

Because I still produce insulin and am insulin resistant (partly cos I'm fat, and partly cos I have PCOS, and partly cos I am on cabergoline, and partly cos I have a weird pituitary gland output), eating carbs tends to result in largish splashes of insulin that are either inadequate or excessive. If I eat carbs, sooner or later, a hypo will happen. If I then add glucose, the seesaw swings violently in the other direction, then back, and so on. A self perpetuating vicious cycle.

Best to hop off the merry go round and live a happy chirpy life in ketosis!

I just wish I stuck with it...

I had one of these a couple of weeks ago. For some reason, whenever I have a fasting test, I have a hypo in the morning and in the past I've had to eat before I get to the surgery and say 'this isn't a fasting one now'. This time, I was going round to a friend's house in the evening and so had an earlier tea than normal at 7m. I was told no food after 9pm. During the day, i'd deliberately given myself less insulin than normal and did the same at teatime in an attempt to not have a hypo. At 8.45pm I gave myself 4xBelvita biscuits as another attempt to stave off the hypo. By 7.15am the day of my test my blood sugars were at 2.7!!!!

Thankfully hubby had decided to go into work later so that he could drop me off at the surgery rather than me walking the 30 minutes to the surgery or taking 2 buses which would have taken at least 40 minutes (lot of waiting inbetween the 2 buses).

My appointment was at 8.20am and the nurse didn't seem at all perturbed when I told her my blood sugars had been so low over an hour earlier.

So, as for this liver dump, I don't seem to get it when my sugars are low, but it's irrelevant for the bg test as that's testing over a few weeks not just the day of the test. The fasting is to do with the cholesterol test but I don't know why you have to fast for that. That's my understanding of it, anyway. I could be wrong.

@Kathleen Mc, that sounds a lot like your basal dose is too high, and you should maybe shift some of your Total Daily Dose from basal to bolus.

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Bluetit1802 said:

Blimey. I wish I hadn't asked now! Thank you Brunneria and Spiker. I can't imagine how horrible it must be. I know Type 1's carry glucose round with them wherever they go. Do you think Type 2's should also do this, whether on meds or not?

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I agree with Brunneria; even though I am T1, a main cause of hypos for me is too many carbs. More carbs mean bigger insulin doses which mean bigger insulin dosing errors which mean more frequent, more severe hypos.

I think a T2 on insulin or insulin-stimulating meds would be wise to carry glucose. If you are just on insulin-sensitising meds (or none) it's much more a personal choice.

I want to reiterate that the hypos Brunneria and I described were severe, and rare. You shouldn't worry unduly, particularly not as a T2. But it is good to treat as something to be avoided. We didn't even get into the fatality statistics...

Spiker said:

@Kathleen Mc, that sounds a lot like your basal dose is too high, and you should maybe shift some of your Total Daily Dose from basal to bolus.

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Many thanks. I have a hospital appointment on Monday and will ask the doc. I was only changed from novomix to lantus and novorapid in feb so still in the learning stage!

I agree with Spiker - I only ever have hypos on the days where I eat more carbs. On days where I strictly limit my carbs my bg is steady all day.

I've been reading the early posts and have a couple of questions.

I was diagnosed at the end of November. I had an HbA1c test then another to confirm it. I then had a follow up mid February. Non of the tests was fasting. I'm going for my 3 month Update HbA1C tomorrow morning 8:45 am. Should I have my breakfast first?

I had thought the cholesterol levels also came from the HbA1c but, after reading here, it seems not?

I made the appointment for tomorrow's test because I knew it was due but couldn't get to see the nurse beforehand. Will the blood clinic know to test for cholesterol as well or should I mention it tomorrow? I'm seeing the nurse in a couple of weeks. Actually I may make an appointment to see the doctor before then when the results are through. I want to see if a reduction in metformin is possible.

Thanks in advance.


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peacetrain said:

I've been reading the early posts and have a couple of questions.

I was diagnosed at the end of November. I had an HbA1c test then another to confirm it. I then had a follow up mid February. Non of the tests was fasting. I'm going for my 3 month Update HbA1C tomorrow morning 8:45 am. Should I have my breakfast first?

I had thought the cholesterol levels also came from the HbA1c but, after reading here, it seems not?

I made the appointment for tomorrow's test because I knew it was due but couldn't get to see the nurse beforehand. Will the blood clinic know to test for cholesterol as well or should I mention it tomorrow? I'm seeing the nurse in a couple of weeks. Actually I may make an appointment to see the doctor before then when the results are through. I want to see if a reduction in metformin is possible.

Thanks in advance.


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At my practise, I pick up a printed form for the bloods, which lists the tests to be undertaken, the vials the blood should be collected in, and whether any of the tests require fasting. This is electronically signed by a doctor. I hand that to the phlebotomist at my appointment and she follows those instructions.

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peacetrain said:

I've been reading the early posts and have a couple of questions.

I was diagnosed at the end of November. I had an HbA1c test then another to confirm it. I then had a follow up mid February. Non of the tests was fasting. I'm going for my 3 month Update HbA1C tomorrow morning 8:45 am. Should I have my breakfast first?

I had thought the cholesterol levels also came from the HbA1c but, after reading here, it seems not?

I made the appointment for tomorrow's test because I knew it was due but couldn't get to see the nurse beforehand. Will the blood clinic know to test for cholesterol as well or should I mention it tomorrow? I'm seeing the nurse in a couple of weeks. Actually I may make an appointment to see the doctor before then when the results are through. I want to see if a reduction in metformin is possible.

Thanks in advance.


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Hi,

You don't have to fast before an HbA1c. The test result is an average of your blood glucose over the last 8-12 weeks, so what you do on the morning of the test is irrelevant. So enjoy that breakfast!

I'm afraid I can't comment on cholesterol tests, since I don't know enough about them.

Last time I had some blood tests they ran a cholesterol as standard, and since they never came back to me with results, I assume it was OK...

The only reason to fast is that a really crazy blood sugar will skew the HBa1c. So no need to fast, just don't have a box of Krispy Kremes. Wait until after the blood draw. ;-)

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