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Blood sugar test (random/ fasting) – Procedure, Preparation and Test Results

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Why is the blood sugar test done?

This blood sugar test is done to check the glucose level in your blood. The test allows you to know if your blood glucose level falls under a normal range or an abnormal range, which could be either high or low.

The blood sugar test allows to screen you for diabetes or prediabetes status.

When is blood sugar test done?

This blood sugar test is typically done in the following situations:

• When a person’s age is above 45 years and has a risk for developing diabetes

• When you have diabetes

• When you develop symptoms suggesting high or low blood glucose levels

• When you are pregnant.

Procedure of Blood Sugar Test – What sample is needed, and how is it collected?

Blood sugar test procedure consists of the details about how the blood sample is collected:

• The blood sample is taken from a vein in your arm, especially from your elbow fold.

• If you have diabetes, then you might need to take a small drop of blood as a sample. This is done by pricking your finger tip with a lancet, which is then touched with the sensor of the glucose monitor. You may need to do this, 3 to 4 times in a day to properly track your glucose levels.


• An alternative to this is to use a continuous glucose monitor, where a sensor is inserted under your skin, which measures your blood glucose levels at regular intervals.

What are the preparations needed before the blood sugar test?

Before getting prepared for a blood sugar test following are the steps a person needs to follow:

• Fasting sample: For screening, typically, your doctor or lab technician will advise you not to drink or eat for at least 8 hours before the blood sugar test. You can only take water if you want to drink anything.

• Fasting and postprandial sample:If you have diabetes, your doctor may advise you to give two samples one before eating anything and another after eating food. These samples are called fasting and post prandial blood glucose samples, respectively.

• Fasting and timed sample: in specific tests such as glucose tolerance test, your doctor would ask you first to give a fasting sample followed by several samples after drinking a glucose-rich drink.

• Random sample: sometimes, your doctor would take a blood sample irrespective of when you had your meal.

What is tested?

The purpose of the blood sugar test is to measure the level of glucose present in your bloodstream.

Glucose is the main source of energy for the cells of the body. A relatively constant supply of glucose is needed to be maintained in the blood to be available for the cells to function properly. Abnormalities in the level of glucose in the blood can lead to various complications and chronic issues.

When the food containing carbohydrates is digested in the gut, it releases glucose, which is then absorbed into the bloodstream to be used by the body cells.

The insulin is a hormone that is released by the pancreas, which plays the central role in the utilization of blood glucose by the body cells. It acts as a key that allows the glucose to be entered into the cells. With inadequate or no insulin, the glucose remains unutilized by the body cells, which in turn causes a high level of glucose in the blood.

In diabetes, due to deficiency of insulin or resistance to insulin, the body cells are unable to utilize the glucose. This causes excess glucose to circulate in the blood, which may lead to conditions such as blurred vision or blindness, heart disease, and damage to the kidney or the nervous system.

On the other hand, when the glucose levels fall in the blood, the pancreas secretes a hormone called glucagon. The glucagon causes the glycogen stored in the liver to breakdown into glucose and maintain its level in the blood. When this function is affected, it causes fall of glucose in the blood, which may cause brain or nerve damage or even life-threatening situation.

So, by measuring the normal or abnormal levels of the glucose in the blood, the doctors are able to detect and manage the condition better and prevent further complications.

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What does the blood sugar test result mean?

Raised glucose levels typically occur due to diabetes, but it can also occur due to other conditions and diseases.

The results of a blood sugar test with their interpretation is given below:

Random Blood Glucose

If a person has symptoms of diabetes and his random (non-fasting) glucose level is 200mg/dL or above, then it suggests, the person is suffering from diabetes.


Blood glucose levelInterpretation
Less than 200mg/dLNormal random glucose level
200mg/dL or aboveDiabetes

Fasting Blood Glucose

Blood glucose levelInterpretation
From 70 to 99 mg/dLNormal fasting glucose
126 mg/dL or aboveDiabetes
From 100 to 125 mg/dLPrediabetes (fasting glucose is impaired)

2-Hour Oral Glucose Tolerance Test (OGTT)

The blood glucose levels are applicable except during pregnancy.A blood sample is taken 2 hours after drinking a liquid containing 75-gram glucose.


Blood glucose levelInterpretation
Less than 140 mg/dLNormal glucose tolerance
200 mg/dL or aboveDiabetes
From 140 to 199 mg/dLPrediabetes (glucose tolerance- impaired)

Gestational Diabetes single-step approach (as an option recommended by the ADA)

Total three blood samples are given, one before the meal and rest two, 1 and 2 hours after drinking a 75-gram glucose drink. Gestational diabetes is diagnosed when any of the values exceed the normal limit.


Sample collection timingInterpretation
Fasting92 mg/dL or above
1 hour180 mg/dL or above
2 hour153 mg/dL or above

Gestational Diabetes Two-Step Approach (as currently recommended by ACOG and as one option from the ADA): Step One

Step One: only one blood sample is given, 1 hour after drinking a 50-gram glucose-containing liquid.


Blood glucose levelInterpretation
Less than 140 mg/dLNormal screen
140 mg/dL and overAbnormal, followed by OGTT (referstep two below)

Note: Some doctors recommend a cutoff of 130 mg/dL,which is believed to identify 90% of women with gestational diabetes, in comparison to 80% women identified using 140 mg/dL as a threshold.


Gestational Diabetes Two-Step Approach (as currently recommended by ACOG and as one option from the ADA): Step Two

Step Two: Diagnostic OGTT, where a total of four blood samples are drawn.First is drawn while fasting and the other three subsequently at 1, 2, and 3 hours after a 100-gram glucose drink. Gestational diabetes is diagnosed if any two or more values exceed the normal level.


Sample collection timingTarget levels
Fasting (prior to glucose load)95 mg/dL
1 hour after glucose load180 mg/dL
2 hours after glucose load155 mg/dL
3 hours after glucose load140 mg/dL

Note:Some laboratories may use different values for normal and abnormal limits.


Elevated blood glucose due to other conditions and diseases

Chronic kidney disease

• Hyperthyroidism

• Cushing syndrome

• Acromegaly

• Pancreatic cancer

• Pancreatitis

• Excessive consumption of food

• Acute stress (response to heart attack, stroke and trauma)


Low blood glucose

Decreased level of glucose in blood gives typically suggests hypoglycemia. This can initially lead to nervous system symptoms such as sweating, hunger, palpitations, anxiety, and trembling. If continued, this may eventually lead to confusion, blurred vision, hallucinations, coma, and even death.

The following conditions can cause low blood glucose:

• Hypothyroidism

• Chronic kidney failure

• Hypopituitarism

• Severe liver disease

• Severe heart failure

• Severe infections

• Insulin overdose

• Starvations

• Insulin-producing tumors

• Adrenal insufficiency

• Use of glucose-lowering products

• Drinking excessive alcohol

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