Fasting blood sugar

Blood sugar testing measures how much glucose is in the bloodstream. No matter what is eaten, from a small snack to a large meal, blood glucose values rise in response to any carbohydrates that are digested.

In a healthy person, the pancreas reacts to the higher blood glucose by releasing insulin, a hormone that converts blood sugar into usable energy.

In addition to carbohydrates, other body processes also raise blood sugar levels.When a person fasts, which is defined medically as not eating or drinking anything aside from water for at least eight hours, the release of glucagon is triggered in the body. Glucagon instructs the liver to metabolize reserve supplies of glycogen, which are then circulated into the bloodstream as sugars. Accordingly, the amount of plasma glucose goes up. This is how the body creates energy even while fasting.

In sum, when diabetes is not present the body responds to all blood sugars by manufacturing insulin in proportion with the glucose level. When it comes to fasting blood sugars, insulin lowers and stabilizes the levels so that they remain in a normal, healthy range. Yet when any form of diabetes is present, either pre-diabetes, Type 1 diabetes or Type 2 diabetes, the whole physiological process doesn’t work correctly, and blood sugars are often considerably higher than normal. The fasting blood sugar test (FBS) is commonly used to detect the existence of diabetes.

In order to prepare for a fasting blood sugar test, one must refrain from eating or drinking from eight to twelve hours before the test, depending upon the doctor’s instructions. It is conducted in the same manner as any laboratory blood test. The health professional will wrap an elastic band around the upper arm in order to restrict blood flow, which enlarges the veins and facilitates the insertion of a needle. After disinfecting the site with alcohol, a needle is placed into the vein and blood is drawn into a vial, which will be then be sent for laboratory testing.

A normal result for fasting blood glucose ranges from 70 – 100 mg/dL. According to criteria set by the American Diabetes Association, a higher than normal fasting blood sugar between 100 to 125 mg/dL (5.6 to 6.9 mmol/L) may indicate prediabetes. This shows an increased risk of developing Type 2 diabetes.

When the measurement is above 126 mg/dL (7 mmol/L), a diagnosis of diabetes is likely. A lower than normal result may point to hypoglycemia that is caused by a specific type of tumor in the pancreas, and further diagnostic testing is needed.

Besides eating or drinking during the eight hours before the fasting blood sugar test, other factors may influence the outcome. Illness, drinking alcohol or excessive caffeine the day before, smoking and emotional stress can all impact blood sugar levels. Fasting blood sugar tests should therefore be performed twice, on two separate days, in order to confirm that results are consistent.

19 Comments - Leave a Comment
    • Sherry King -

      Yikes… My head hurts so bad if mine gets over 200… I don’t take meds for type 2 diabetes yet… But fear I will have to start… 😢

    • Matt Sherman -

      Yes… you no doubt have diabetes. If you haven’t already go to the Dr and get medicine to get that under control.

  • Kpkumar -

    Blood sugar 153 mg/dl (8.49mmol/l) fasting
    After 2 hrs (post BreakfastI it is Bood sugar 94 mg/dl (5.22mmol/l)

    can you let me know i am a diabetic i have patient. i have checked up my diabetic profile 1 yrs back it was normal
    please let me know

  • Linda Dudek -

    my blood sugar 3 hours after a no carb breakfast is 269. I take 1 metformin a day. Even when eating my best first in morning the lowest I can get is 133. should I see my dr about maybe increase metformin?

  • Neville pillay -

    Look guys, I am off insulin and metformin….I have been diabetic for twenty years and I only recently got better by simply cutting all carbs out, only allowing leafy greens and a few berries, I’m just fine now…

    • Miss Smith -

      Hi I would like to know more about what you incorporate into your Diet for this wonderful change. And what medications were you on I was diagnosed 9-14and have not been seen by a endocrinologist only given refills via clinic or e r I was taking 1000 mlg I metformin and lantus at night it made me so sick sluggish weak just not well I stopped all meds last year in March and I did great up until 7-15 then had 300+ blood sugars for at least 3months but I started back on met form I. Thinking though it made my stomach hurts violently I stopped what can you tell me

  • esther -

    Myfastingsugar185.after meals 280. So far I dont know ant it now onlyi tested nd find out.kindly gv sugestions

  • chaitanya -

    My fasting sugar level was 110 and again evening I had gone for the test after 3 hrs of having lunch it is 209… pls tell me Iam I affected with diabetes

  • Regina Reyes -

    My hubbys fbs was 255 as recent as 10/19/15…
    He takes tanzium 50mg once a week along with metphormin 100omg. And gabapentin too…
    I want facts of whats instore for him..the good, bad, and gory aspects… i can not get him to understand…. He cannot go without deepfried french fries. Eggrolls. Or hashbrowns.. (hes a carb- whore, exvuse the verbage) Its nothing for him to polish off a 2liter in a meal setting… at this point I want ammo… Im past the subtle hints or gentle comments with this man… i want all the cold hard facts, and outcomes.
    Regina Reyes (wife of a carb whore)

  • sai karthik -

    friends..i am 17 years 6 months old.My Random Blood Sugar came out to be 360 mg/dl . i just don’t know what is going to happen. But i don’t have any of the symptoms like head ache or dizziness e.t.c., please reply

    • Marlene -

      If you ate a lot of carbs in the few hours before, this is what results when you are diabetic. If you drastically reduce all carbs you may be able to avoid medication, but do get retested frequently after new diet. Even if you have no symptoms 360 is doing damage to your organs.

  • Karat Abubaker shaikh -

    I m 44 year today I check my sugar fasting
    After fasting 19.
    Doctor advice me to take insulin morning and evening 10 mg

    • Marlene -

      If it is over 100 you are at risk for developing diabetes in the next few years. It suggests your body is not producing insulin adequately to control your blood sugar perfectly. If you go on a low carb diet, it may function normally. Then retest to be sure the diet is working.

  • Desiree' -

    I had been dealing with anxiety attacks out of no where, shaking, sweats, dizziness and a number of other issues. I began home testing and found that at no point have I ever tested higher than 81. Fasting is 71 and 2 hours after a meal I was at 81… Before bed 79. I have been getting the same numbers for 3 days! but i also feel like crap!

  • Vernon Trexler -

    Never had blood sugar problems in my 69yrs BS is 146 late morn.i am 35 lbs overweight.i think if i lost 20lbs and cut out carbs this is a non factor.what say you.i do exercise

    • Marlene -

      A very low carb diet will improve your blood sugar, you might also still need medication eventually if that doesn’t work.
      I sometimes bet 140, when fasting, then I need a protein/fat snack and blood sugar comes down.

      • Marlene -

        If you test right after exercise, some people have higher blood sugar at that point.

  • Katherine pascal -

    My fasting sugar was 136 . I am a diabetic and last time tested it was 119 . Hadn’t been taking my
    Meds for just a few days . Concerned I may need insulin ?

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