Low Blood Sugar (Glucose) and Hypoglycemia Symptoms

What is hypoglycemia?

The term low blood sugar is commonly used to refer to a drop in blood glucose levels below 54mg/dL or 3mmol/L. This state is referred to as hypoglycemia. In a person with diabetes, a blood glucose level below 63mg/dL or 3.5mmol/L is referred to as hypoglycemia.

Medically, hypoglycemia may be diagnosed by three factors which is known as Whipple’s triad :

  1. Signs and symptoms of hypoglycemia
  2. Low plasma glucose level (as mentioned above)
  3. Resolution of hypoglycemia signs and symptoms once the plasma glucose (blood sugar) level rises

Blood Sugar Levels

The term low blood sugar is often used frivolously to describe a range of symptoms that may or may not be related to a low plasma glucose concentration. There is also confusion relating to the blood glucose levels that can be classified as hypoglycemia.

In some patients, the symptoms of hypoglycemia may be evident at a blood glucose level below 70mg/dL (3.8 mmol/L). This is more frequently seen in diabetics. In others, the signs and symptoms may only be evident as the blood glucose levels drop below 60mg/dL (3.3mmol/L). The blood glucose levels of newborn babies (neonates) may drop as low as 30 mg/dL (1.7 mmol/L) in the first day of life and should be attended to immediately with feeding.


  • Pre-Prandial– Fasting,  Before Meals, Upon Waking
    • In a person without diabetes, the normal fasting glucose levels may be between 70mg/dL (3.9 mmol/L) and 99mg/dL (5.5mmol/L).
  • Post-Prandial– After Eating (1 to 2 hours)
    • After eating, the blood glucose level can rise to, but should not exceed, 140mg/dL (7.8mmol/L).
    • Blood glucose levels below 54mg/dL (3mmol/L) is considered as a low blood sugar level and is diagnosed as hypoglycemia if it meets with the guidelines as per Whipple’s triad.

Diabetes and Pre-Diabetes

  • Pre-Prandial– Fasting, Before Meals, Upon Waking
    • In diabetics, the fasting blood glucose level may range from 70mg/dL (3.9mmol/L) to 140mg/dL (7.8mmol/L).
    • In pre-diabetes (impaired glucose tolerance), the fasting level is usually below 125mg/dL (6.9mmol/L).
  • Post-Prandial– After Eating (1 to 2 hours)
    • After eating, the blood glucose levels in a diabetic may exceed 200mg/dL (11.1mmol/L). This is not ideal and better management should aim to limit the rise in blood glucose levels of diabetics after eating to 180mg/dL (10mmol/L) or less.
    • With pre-diabetes (impaired glucose tolerance), the blood glucose levels after eating is usually less than 200mg/dL (10mmol/L). If it exceeds this level, it is a good indication that the person is a diabetic.

Refer to  Blood Sugar Levels for Diabetes and Impaired Glucose Tolerance (high readings) for more information.

Signs and Symptoms of Hypoglycemia

The signs and symptoms of hypoglycemia can be divided into two categories :

  1. Autonomic
  2. Neuroglycopenic

There are are also general and non-specific signs and symptoms which should not be used in isolation to diagnose hypoglycemia. These general symptoms include nausea, fatigue, and headaches. Often the term ‘low blood sugar’ is used frivolously to explain the cause of these symptoms although other causes could account for it.


When the blood glucose levels drop significantly, the body releases epinephrine. This triggers certain processes like releasing the glucose stored in the liver (glycogen) in an attempt to stabilize the blood glucose levels. Epinephrine also affects the nervous system and results in these characteristic signs and symptoms :

  • Anxiety
  • Dizziness
  • Hunger
  • Palpitations
  • Sweating
  • Trembling

These symptoms are the early warning signs but may be absent in certain cases. In patients who experience frequent episodes of hypoglycemia, the body may stop releasing epinephrine. This is known as hypoglycemic-associated autonomic failure (HAAF) or is also referred to as hypoglycemia unawareness. The blood glucose levels continue to drop until the neuroglycopenic symptoms may be evident. It may only be at this point that the appropriate measures are implemented.


As the blood glucose levels continue to drop without any intervention, the glucose supply to the brain is severely impaired and may result in the symptoms listed below.

  • Blurred vision
  • Confusion
  • Difficulty concentrating
  • Drowsiness
  • Irritability, anger
  • Poor coordination
  • Speech difficulty

Eventually seizures and even a coma may ensue. Changes in behavior at this stage may resemble inebriation (alcohol intoxication, drunkenness) and is sometimes mistaken for alcohol dementia in alcoholics.

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