Your Complete Guide to Blood Sugar Levels

Blood Sugar Levels

“The food you eat can be either the safest and most powerful form of medicine or the slowest form of poison.” (Ann Wigmore)

We exist in an era where we rely more on junk, inorganic, sugary, processed foodstuffs. This unwholesome diet is wreaking havoc on our well-being. Keeping a log of our blood sugar levels should be a mandatory component of our regimen.

This article will highlight the ranges of blood glucose levels on different occasions. However, before proceeding ahead, I will like you to have an understanding of some important terms as follows:

Random blood glucose (RBG):

This is a casual blood sugar test taken in a non-fasting state at any time during the day.

Fasting blood glucose (FBG):

This is the test, measured first at the cockcrow after an overnight fasting of at least 8-12 hours.

Postprandial Blood Glucose:

Postprandial blood glucose indicates the level of glucose in your blood after meals; this could be 1 hour after meals, 2 hours after meals and so on so forth.

Pre-Diabetes (Impaired Glucose Tolerance):

This signifies that the person is not yet in the diabetic range, but has crossed the normal glucose range (i.e. hyperglycemic now). The pre-diabetic has an enhanced risk of insulin resistance and an increased propensity to develop full-blown diabetes.

Oral Glucose Tolerance Test (OGTT/GCT or Glucose Challenge Test):

Blood Sugar LevelsOral means via mouth, glucose tolerance test implies testing your blood glucose levels after giving you a glucose solution to drink. The test is performed in the morning, usually after an overnight fasting of approximately 8-12 hours (no calorie intake, can drink water). A baseline blood sample is then withdrawn at zero time. The person then receives a glucose solution to slurp, (this could be a 50-gram (g), 75-g, or a 100-g glucose solution, depending upon the physician’s orders). The blood samples are then taken at intervals of 1, 2, and 3 hours respectively. In general, the 75-g OGTT requires the 2-hour testing, whereas the 100-g OGTT is a 3-hour interval testing (see below).

The OGTT is principally a screening test for the diagnosis of diabetes mellitus first diagnosed during pregnancy or gestational diabetes mellitus (GDM).


Time of Measurement Normal Blood glucose ranges (Non-Diabetics) Blood Glucose ranges for Pre-Diabetes Blood Glucose Ranges Signifying Diabetes
FBG (in adults) 70-100 mg/dl 110-125 mg/dl ≥126 mg/dl
RBG (in adults) 79-139 mg/dl 140-199 mg/dl ≥200 mg/dl¹
1-Hr After Meals <140 mg/dl N/A N/A
2-Hrs After Meals ≤120 mg/dl 140-199 mg/dl ≥200 mg/dl
3-Hrs After Meals ≤100 mg/dl* N/A N/A
During Pregnancy



Post-OGTT (100 Gm Glucose): **




72.3 ± 6.2 (mg/dl) ²≤140 mg/dl



127.8 ± 15 (mg/dl)

113 ± 12.9 (mg/dl)




>140 mg/dl

≥95 mg/dl≥200 mg/dl
≥180 mg/dl≥155 mg/dl≥140 mg/dl
Newborn Babies

1-2 Hrs

2-3 Days


30-40 mg/dl

≥54 mg/dl

*** (Scroll below)


Some Information Pertaining to the Above Chart

  • N/A = Not Applicable
  • 1 = One reading of a random plasma glucose of 200 mg/dl is sufficient for the diagnosis in the presence of other diabetic signs and symptoms.
  • *At 3 hours after meal, we normally expect the blood glucose to drop as close to the normal fasting levels (i.e. ̴100 mg/dl)
  • **The World Health Organization (WHO) and the American Diabetes Association (ADA) guidelines also include a 75-gram oral glucose tolerance test for confirming the diagnosis of gestational diabetes. Either the physicians can go with the one-step-strategy of a 75-g glucose load, or alternatively, with a two-step strategy in which, the doctors initially perform a 50-g oral glucose load and if the blood glucose measured after an hour is greater than 140 mg/dl, they proceed ahead with the 100-g OGTT. You then glug down a 100-g glucose solution and the blood samples are drawn at 2 hours and then at 3 hours (time measured from drinking the solution) respectively.

75-g OGTT Criteria for the Diagnosis of GDM

Following are the criteria as recommended by WHO for the diagnosis of GDM:

  • FBG: 92-125 mg/dl
  • Following a 75 g-OGTT (two hours post-OGTT): 153-199 mg/dl

(One or more lab values should be positive to establish a diagnosis of GDM after a 75-g OGTT).

The American Diabetes Association (ADA) lists similar reference values (as aforementioned in the table) to establish the diagnosis of GDM. Following are the criteria as suggested by ADA to diagnose GDM after a 75-g OGTT:

  • FBG: 95 mg/dl
    After a 75-g oral glucose load (2):
  • 1 h: 180 mg/dl
  • 2 h: 155 mg/dl

(Two or more of the above positive lab parameters indicate GDM).

The ADA recommends screening for GDM between 24-48 weeks of gestation in females not previously diagnosed with diabetes

Diabetes in Newborn:

It is uncommon for newborns to develop diabetes. However, there is a condition called transient diabetes mellitus of newborn, defined as raised blood glucose levels (> 215 mg/dl) occurring within the first 4 weeks of life with a necessity of insulin therapy.

HbA1c and its Significance in Diabetes

ADA integrated another lab parameter for detecting the average blood glucose in the past three months. HbA1c is a glycated form of hemoglobin that reflects the prior glucose control in the past 3 months. The HbA1c forms when hemoglobin (Hb, a protein within the red blood cells) combines with glucose (glycated) and glucose holds on to the Hb for 120 days (i.e. the lifespan of red blood cells). When the levels of blood glucose are normal, the HbA1c is normal; likewise, hyperglycemia accentuates the HbA1c levels as well. Physicians also utilize it as a diabetes prognosis tool (i.e. the higher the HbA1c, the greater is the risk of developing diabetes-related complications).

HbA1c Levels:

  • Normal = <5.7%
  • Pre-diabetes = 5.7% to 6.4%
  • Diabetes = ≥ 6.5%

(P.S. Levels less than 6.5% in the presence of other positive glucose tests do not exclude diabetes).


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