Fasting blood sugar verses HbA1c

Caterham said:

I have noticed that the most popular threads on here are the ones with morning fasting rates, that a lot of people post in every day (Some have really low figures) My fasting rates average 6.2 to 7.1 (More 6 than 7) with the occasional 5. The figures seem unrelated to what I eat, and I have stopped worrying too much about it as nothing I do seems to affect it.

I was talking to my doctor, who has a modern view on diabetes and lower carbing, and his view is that he discounts almost completely the fasting figures, and concentrates solely on the HbAc1 reading, as that is the best overall measure.

Is there a general view on this? My Hb figure is generall OK, at 41/42 for the past 2 years, and he is very happy with that.

What do others think, or should I put some more effort into the fasting figures? I am current eating a pretty steady 140g of carbs a day.

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Clearly the HbA1c is the figure the medics now use to view/judge your control, but clearly that's an average. For me, keeping an eye on my other bloods (fasting and meal related ones) is a bit like looking after the pennies, then the pounds look after themselves.

For me, the best way to have half a clue what my HbA1c is going to be is to have a handle on the other readings.

140 grams of carbs/day is about 700% more than I eat per day. I am sure that you could improve your FBG results by making a reduction in your carbohydrate intake. You can easily put this to the test and see for yourself.

Fasting readings are notoriously fickle because other things come in to play that we have little control over, most notably the Dawn Phenomenon but also how well we sleep and consistency in timing the morning test.

The HbA1c is an average, but it doesn't tell us how high or high low we go. It is the highs that matter most, which is why I test fasting plus before and after some meals and at bedtime, and chase any highs to make sure I am coming down again.

My GP practice no longer does fasting blood glucose testing for diagnosed diabetics (just HbA1cs) because of the unreliability and variability.

I might have agreed with your doctor a week ago, but am not sure now. I had two hba1c tests a week apart this month. It jumped from 34 to 39 in one week for no obvious reason. I would worry now if I were to rely on a yearly or even quarterly test to know how I was doing. It could be up and down like a dog's leg. The hba1c is weighted to the end of the test period so it won't tell you if you are doing badly at the start of the 3 month period. I will keep a tight rein on things by testing daily.

I have similar problem, and it doesn't matter how much carbs I eat. I eat about 140-150 grams of carbs per day as well. So naturally, my first idea was to try and lower my carbs intake, especially for dinner. I also tried to have dinner earlier and no snack. I tried doing more exercise in the evening.

Result - zero changes in the FBG and one ****** off doctor. >.> She scolded me like a brat for 'silly experiments". She also assured me it's nothing to worry about, as all my other readings during the day are fine (I do tests 7 times per day, and my average before meal 5.3 and after meal 6.0), and HbA1C is good (6.5, compared to 11 three monts ago).

So I say - trust your doctor

Hi Caterham,
I have the biggest problem with my fasting BS as my liver seems to hate me in the morning, I tried for a while not taking a fasting test, but then found it difficult to judge if my breakfasts were ok because I usually get a huge liver dump. By looking at the trend these figures give me, I am able to adjust my eating habits etc to help retrain (I hope) my liver and lower my readings. It's a personal thing, it may not help my doctor.... But it definitely helps to keep me motivated

Sigalit said:

I have similar problem, and it doesn't matter how much carbs I eat. I eat about 140-150 grams of carbs per day as well. So naturally, my first idea was to try and lower my carbs intake, especially for dinner. I also tried to have dinner earlier and no snack. I tried doing more exercise in the evening.

Result - zero changes in the FBG and one ****** off doctor. >.> She scolded me like a brat for 'silly experiments". She also assured me it's nothing to worry about, as all my other readings during the day are fine (I do tests 7 times per day, and my average before meal 5.3 and after meal 6.0), and HbA1C is good (6.5, compared to 11 three monts ago).

So I say - trust your doctor

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You're lucky to have three monthly HbA1C tests. My doctor will only allow annual tests. If you were to end up with annual tests, you'd be very unwise not to test in the interim as you'd have almost no idea what your numbers were like. As it is, you're on insulin therefore you're likely to get more frequent HbA1C tests. Us diet-controlled T2s are largely left to fend for ourselves.

So no, I wouldn't trust my doctor if she said don't test. Fortunately, I haven't seen her since diagnosis in April 2013 and I never bothered to discuss home testing with the DN when I last saw her in August 2014 as I was pretty sure what her answer would be.

julifriend said:

You're lucky to have three monthly HbA1C tests. My doctor will only allow annual tests. If you were to end up with annual tests, you'd be very unwise not to test in the interim as you'd have almost no idea what your numbers were like. As it is, you're on insulin therefore you're likely to get more frequent HbA1C tests. Us diet-controlled T2s are largely left to fend for ourselves.

So no, I wouldn't trust my doctor if she said don't test. Fortunately, I haven't seen her since diagnosis in April 2013 and I never bothered to discuss home testing with the DN when I last saw her in August 2014 as I was pretty sure what her answer would be.

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Um. I'm sorry, could you please show me WHERE I said 'don't test', or where I claimed my doctor said that? I said I test seven times per day and my doctor said not to worry about FBG since all my other readings AND HbA1C are good.

And, well, you chose to be left to fend for yourself - you decided to ignore your doctor and 'didn't bother' to talk to her for almost two years now.

I decided to respect my doctor's opinion and to follow her advice, since she's an expert with long practice. Frequent discussions, personally or via the phone and all kinds of tests come with that. And so far, I'm quite happy with the results. I see no reason why I should struggle with all kind of problems, questions or worry alone, when there's an expert willing to help.

@Caterham

If you can eat 140g carbs a day and maintain an hba1c of 41/42 with only 2 metformin, then I think you are doing fantastically!

I've had to cut my carbs below 50g/day to get stop spiking above 8mmol/l with food.

Dawn phenomenon seems to have a mind of its own (mine is mainly affected by stress, I think), so unless I start on sedatives, I'm kinda stuck with mine.

And I totally agree that using insulin makes it a totally different experience from dietary control.

Caterham said:

Thanks for all the replies, as always interesting reading.

Last night was a case in point. I had some chicken, 8 boiled small potatoes and some peas, with smoked salmon and a slice of wholmeal to start. Total carbs about 47. I was 5.6 after 2 hours just before I went to bed. This morning, 6.7!

Pasha - From what you are saying you eat 20g of carbs a day, which to me seems too low (But if you are happy, great!) I would struggle with this amount, although I could get to 100g fairly easily I think.

Brunneria - Thanks for the reply. I think I am doing OK, but I do monitor it. I was very overweight, and I think the 3.5 stones I have lost has made a big difference. Plus at 140g a day carbs is about a quarter of what I used to eat.

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Complete speculation, but it could have been your 5.6 wasn't at the peak, or on the fall back. You could still have been rising?

I must admit, my lifestyle tends to mean I am eating more than two hours before going to bed, so I have opportunities to prove (or disprove) that sort of hypothesis, and also it means my fast is a bit longer than yours is likely to be. That may, or may not have an impact.

But, that seems like quite a lot of carb to me, so close to bed. Looking on a couple of websites, I can't find anywhere that 8 potatoes alone could get down to 50g. The value on the screenshot below is for 1 large potato, but I possibly considered if you had 8 little ones, it might have been a decent equivalent? (According to that website, 8 small ones would be over 200g......)



If your 5.6 is indeed either your peak or beyond it, you are doing extremely well. In your shoes, I might try that meal again, and test again after a further 30 minutes to see what's happening then. If it's falling, fine. If it's level or rising, try again in a further 30 minutes.

It would also be interesting to see where your day to day bloods went on a trimmed back carb level, but it's entirely your call if you want to do that.

I also was a bit confused by your calculation of 47g carbs for that meal. I calculated it to be at least 60g depending how many peas and what type of bread. New potatoes boiled are about 5g carbs each. A small portion of garden peas is about 5g carbs, so that makes 45g carbs before your bread. I agree the 5.6 at 2 hours appears very good, but unless your pancreas is working really well, maybe a bit unrealistic for a peak? If it was your true peak, I am very jealous.

I have a problem being overweight, although it does not affect my lifestyle too drastically. I would like to lose a stone for my own comfort but using Insulin does seem to have hindered me with this. I was put on Humulin 1 last September and am now using 50 units per day., My weight has gone up by around 2 kgs, my H1bAc has gone from 10.0 to 7.4, I am waiting for my next diabetic nurse appointment for advice. My fasting readings are around 6 but my evening readings vary from 7 to 11. All the chat about carbs v fat v sugar are confusing me.