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Is Fasting Blood Glucose Level Of 4.8 A Cause For Concern?

Posted on Thu, 13 Aug 2015

Question: Hi,
I have asked previously about my eye cataract, possibly caused by diabetes. I have the results back from the blood test with a fasting blood glucose level of 4.8 considered to be below the level for diabetes. Previous results were 4.7 on 6th Nov 2014, 5.2 13th Aug 2014 and 4.8 14th XXXXXXX 2013. Is it still possible that I could have diabetes or pre-diabetes and should I ask for the GTT? Or is the Hba1c test? Which of these tests is more accurate in diagnosing diabetes or pre-diabetes?

I also wonder whether the amount of time to last meal could affect result, in my case about 18 hours to the last meal since blood test about noon. Also, I did take a lot of water, would that dilute the blood and affect the test results? (lower blood glucose concentration than would normally be expected?)

Thanks,
Regards.

Answered by Dr. Ajish TP (23 minutes later)

Brief Answer:
These things will change the reports

Detailed Answer:
Hi,

Welcome to HCM. I have gone through the question and understand your concerns.

The answers to your questions:

1. Fasting of 6-8 hours is recommended for doing fasting blood sugars. When you fast long there will be an initial drop in blood sugars after which it will increase due to the effect of stress hormones. So fasting glucose after 18 hours of fasting is not reliable.

2. Increasing fluid intake will dilute the blood, but the change in blood sugar values will be only small.

3. It's better to do an HbA1c as it is more useful in follow up and is not changed by daily food intake or period of fasting.

Hope I have answered your questions. If you have any further queries I will be happy to help you

Regards,

Dr Ajish TP [MD,DM]
Consultant Endocrinologist

Above answer was peer-reviewed by : Dr. Chakravarthy Mazumdar

Follow up: Dr. Ajish TP (3 hours later)

Thanks Dr Ajish,

I will try to arrange to HbA1c test as my current GP said it's not really recognised under Australian medical system.

So, to clarify as the fasting period was longer than usual in my case the test results are likely to be higher than normal due to effect of stress hormones. It should mean that diabetes is unlikely as blood sugar levels after 6-8 hours would be even lower?

Thanks,
Regards.

Answered by Dr. Ajish TP (9 minutes later)

Brief Answer:
Better to repeat the tests

Detailed Answer:
Hi,

Welcome back.

We cannot predict that - if you are on prolonged fast your sugars can be either low due to fasting or high due to stress hormones. This will vary for different people as the body's response to fasting is not same for everyone. So we cannot conclude that the sugars after 8 hours will be lower than this.

You should repeat the blood tests properly - fasting after 6-8 hours fast and after food ( or a GTT) after 2 hours if you can't do an HbA1c in your insurance system.

Regards
Dr Ajish TP

Above answer was peer-reviewed by : Dr. Chakravarthy Mazumdar

Follow up: Dr. Ajish TP (3 hours later)

Thanks Dr. Ajish,

I will try to repeat the test. I was not aware that 6-8 hours fasting is recommended for the test. Would you recommend a midnight meal with 8am test or 8am meal with 2pm blood test or would it not really matter? I am thinking the metabolism will slow during sleep.

Thanks,
Regards.

Answered by Dr. Ajish TP (58 minutes later)

Brief Answer:
After last meal at 10 -11 pm, you can do test at 6-8 am

Detailed Answer:
Hi ,

Welcome back.

Usually we recommend patients to have dinner at 8 pm, a small snack at 10-11 pm (this is the normal diabetic diet that is recommended) and do a fasting blood sugars at 6-8 am.

We usually do fasting and after food blood sugars before and after break fast. This is because chance of detecting diabetes is high during that time. (THEORY: the blood sugars are more during morning hours - due to hormonal effects (Cortisol) and some thing called hepatic glucose output)

So it is preferred to do fasting sugars at 6-8 am and not at 2pm.

Metabolism is slow during sleep, but our body produce more glucose at night. (THEORY: Hepatic gluconeogenesis - liver producing glucose from proteins and other substrates- is more during night making the fasting sugars higher before breakfast than before lunch or dinner)

These tests are SCREENING tests for diabetes. So even when one value is high that means you are having pre-diabetes or diabetes - low values won't always rule out diabetes.

Hope the information was useful. Delete the THEORY part if it is confusing.

Regards
Dr Ajish TP

Note: For further follow-up, discuss your blood glucose reports with our diabetologist. Click here.

Above answer was peer-reviewed by : Dr. Chakravarthy Mazumdar