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Relevance of fasting blood glucose to diabetes control

S

sns3guppy

Member
Messages
14
Type of diabetes
Type 2
Treatment type
Tablets (oral)
It's different every day, but I really think fasting glucose is a poor metric and given far too much credence over better measurements such as time in range. Post-meal readings are far more significant, as are the spikes or fluctuations, rather than the absolute values. I typically see about 80-100 mg/dl in the morning, but the Libre sensor often shows low 60's. On the average, fasting, about 90ish, but my days and nights get flopped so frequently, it's really hard to say. I have zero consistency in sleep times, time zones, meal times, or medication times, as none of that is possible for me. Fasting glucose, like A1C, are not the panacea they're cracked up to be, and both can be very misleading.
 
I think it largely depends on what it is you want to know, really... For a diabetic, morning fasting blood glucose is likely to be higher than a non-diabetic due to dawn phenomenon. It's not so much the exact number, I think it's more that higher numbers are indicative of a insulin sensitivity problem. The HbA1c is useful if you want to know whether you're making progress or not with blood sugar control, it can let a surgeon know whether your body is capable of healing after scalpel-work, it'll explain why you might be having symptoms, or none at all. Testing before and 2 hours after a meal will tell you whether your body could deal with what you put in there, but it'll miss the spike. It's basically all relative, with little absolutes in there anywhere.... But it's something to work with, a bit of a guide. Not sure if that makes any sense? But that's what it means to me, by and large.
 
I rely on my morning fasting BG as it gives me an indication of my progress and whether I’ve had too many carbs the previous day. If my insulin levels are high I don’t lose weight which I think is typical of most T2 diabetics and I need to lose weight and get my blood pressure down!
As @JoKalsbeek said, surgeons won’t operate unless your hba1c is under 69mmol/l (I live in the UK), as a higher reading impedes recovery.
We’re all different (stating the obvious :joyful:) and I think we all can decide whether we rely on these numbers or not and luckily as a T2 most of us can request the test for free on the wonderful nhs!
 
Personally I very rarely test my fasting BG. These days I do a week of testing once a year, that's all. The information isn't that useful to me. It does give you some indication of what your liver's up to, but what can you do with it?
 
KennyA said:
Personally I very rarely test my fasting BG. These days I do a week of testing once a year, that's all. The information isn't that useful to me. It does give you some indication of what your liver's up to, but what can you do with it?
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I do a fasting test every day. I use it as an indicator of how my overall sugar control is doing. But I also use it as a starting point for my food choices for the day ahead.
 
I measure my FBG, even though I don't currently have a specific use for it. I’ll record it anyway, as one day it might be useful. What was never recorded can never be analysed after all.
 
I test my FBG too, even though most of the time I'm wearing a CGM. I find it a useful indicator to see how my basal or base line insulin is doing. My base line was hovering between 6 mmol/ls - 7 ish a year or so ago. I increased my exercise regime , plus I started to take meds that increased insulin production. It went down quite a bit, high 4's . It's been rising again. With my standard exercise routine it's around 6 mmol before any DP rise. With aerobic and anaerobic exercise it drops back into the 5's. So I find the FBG useful.
 
This thread is a great reminder that no single number tells the full story. Fasting blood glucose can be useful for spotting trends or gauging liver output, but like @JoKalsbeek and others said, it’s only part of the picture. Time in range, post-meal spikes, and overall patterns often give more actionable insight, especially with CGMs.
 
Resurgam said:
I have not checked my fasting level for years - as I can't do anything about it.
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Me neither but it gives me a pointer as to how high my next HbA1c could potentially be if I take first (usually highest) reading of the day as "average" in the BG/HbA1c converter. That way I can be ready and armed when it gets close to 70, the level at which I will apparently be threatened with an SGLT2i drug I don't want to take.
 
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