Is my assumption correct

I think you are being over simplistic, but you should be pleased that your figures have come down, without attempting to predict the future.

If all you have is this two figures, then it is impossible to guess what the trend is.

For example, the following monthly figures would all give you the same 3 monthly averages, but the last month differs significantly

45,45,45, 43,42,41 (i,e. steady beforehand, coming down gradually afterwards)
45,45,45, 42,42,42 (i.e. steady beforehand, big decrease on diet change and then steady)
40,45,50, 50,42,34 (i.e. rising rapidly beforehand, dropping rapidly afterwards).

And that is just some of the many, many possibilities and also ignores the fact that it is sometimes hard to keep up with a significant diet change and hence sometimes the figures improve and then slip back slightly after a few months.

You might think that some of those scenarios are more likely than others, but mathematically there all give the same results.

No. The A1c haemoglobin molecules that the test looks for have an average lifespan inside the body of about 3 months. Each test returns an average A1c level within your bloodstream over the preceding 12 weeks or so.

You've been on a downward trend (well done!) but it's not really possible to extrapolate these two results to a current "score" of 37.

If you want to know exactly what your blood sugar levels are right now then a glucose meter can be helpful. A meter and test strips will report your level at that instant (within some margin of error) and allow you to monitor your progress in a more immediate way.

thompsi said:

I'd like to think I'm currently well below the 42 level?

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Best way to see is to get a home blood glucose meter and take regular finger prick tests. Although they won't be exactly comparable you'll be able to see the direction of travel and variety which will probably give you more useful info than a fairly infrequent HbA1c.

The downward trend is encouraging. When you say that you changed your diet significantly could you tell us what you did please? There may be other changes that you could make that would further reduce your HbA1c.

thompsi said:

Three months ago I was diagnosed as prediabetic with a Haemoglobin A1c value of 45. I changed my diet significantly and here we are (just tested) three months later with a value of 42. My understanding is that this value represents the "average" level over a three month period. If it was 47 three months ago and now 42 am I right to assume that the current level is circa 37 - (average of 47 and 37 is 42). I know this may be over simplistic but I'd like to think I'm currently well below the 42 level?

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I think that one flaw in your argument is to say " now 42 am I right to assume that the current level is circa 37". It has to be one or the other and it was measured as 42.

Your question probably asks if your current instantaneous blood sugar levels are lower than ever and we don't know because you have not given us those.

The blood cells that were present for the 45/47 reading have all gone now and the new reading measures the cells that have been around for the latest 3 months. During this time you could have had highs, lows etc. and all we can say is that the 42 is an average reading of those. There is no other evidence.

From what I’ve read you’re a1c measurement indicates your average glucose over the previous 2-3 months so your reading today should fully reflect the effects of your diet. One thing that confuses me though is that red blood cells live for about 120 days so, assuming an even age distribution of cells, about a quarter of your pre-diet glycosylated hemoglobin must still be circulating and perhaps skewing the result.

I have the same situation, was diagnosed with a1c of 10% 9 weeks ago and will have another a1c test this week, I’ll l ask my doctor how he interprets the result.

SwissT2 said:

From what I’ve read you’re a1c measurement indicates your average glucose over the previous 2-3 months so your reading today should fully reflect the effects of your diet. One thing that confuses me though is that red blood cells live for about 120 days so, assuming an even age distribution of cells, about a quarter of your pre-diet glycosylated hemoglobin must still be circulating and perhaps skewing the result.

I have the same situation, was diagnosed with a1c of 10% 9 weeks ago and will have another a1c test this week, I’ll l ask my doctor how he interprets the result.

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The more recent weeks have a greater influence on HbA1c than the earlier weeks. The last month contributes more than 50% of the total glycation so the effect of ignoring the period 90 to 120 days ago is insignificant.

Mr_Pot said:

The more recent weeks have a greater influence on HbA1c than the earlier weeks. The last month contributes more than 50% of the total glycation so the effect of ignoring the period 90 to 120 days ago is insignificant.

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Yes of course, any 'old' hemoglobin still circulating had only a brief exposure to levels of glucose of 3 months ago. I hadn't thought of that.