diagnosis of diabetes mellitus & gestational diabetes in 2020

diagnosis of diabetes mellitus-glucometer

Diabetes is a major health problem and prevention is better than cure,but if you feel that you or any your family members has diabetes mellitus then, you must be wondering what is the diagnosis of diabetes mellitus?

If this question is haunting you.Then let me help you.

In this article we will discuss How to diagnose diabetes mellitus or what is the diagnosis of diabetes mellitus and all related diseases like gestational diabetes mellitus.

Hemoglobin (A1C) test-

  • The A1C test is a blood test that depicts the average levels of blood glucose over the period of 3 months.
  • Haemoglobin which is a  oxygen carrier protein in the red blood cells.
  • In blood the blood sugar is bound to haemoglobin.
  • In A1c testing we  measure blood sugar that is bound to the haemoglobin,
  • The higher the levels of glucose in the blood, the higher the amount of glucose  attached to the haemoglobin molecule .
  • It is expressed in the form of percentage.
  • Like other tests this blood test, doesn’t require a person to be fasting.
  • (Other names of this test are:  hemoglobin A1C, HbA1C, glycated hemoglobin, and glycosylated hemoglobin test)
  • According to newer guidelines hemoglobin A1C  is to be used as a screening tool for prediabetes or diabetes

Interpretation of the HbA1c values in diagnosis of diabetes mellitus.

Less than 5.7%


Between 5.7 – 6.4%


6.5% or higher


To say a person has diabetes  the A1c values should be  6.5 percent or higher on two separate tests.

There are certain conditions which makes the A1c test inaccurate , and those conditions are:

  • Pregnancy
  • Person who has anemia
  • an uncommon form of hemoglobin (known as a hemoglobin variant)

in such cases the doctor might ask to do other tests for diagnosis of diabetes in them.

A1C test results may be falsely high or low in certain races,  such as:

  • Africa
  • Mediterranean
  • Southeast Asian descent

Random blood sugar test


  • As the name suggests the blood sample is taken at a random time.
  • It is taken regardless of your last meal.
  • That means you do not have to fast overnight for this test.

This test  along with the symptoms like, increased frequency of urination , increased thirst ,increased hunger, unexplained weight loss, non healing sores, fatigue, blurring of vision etc. helps in diagnosis of diabetes

a random blood sugar level of 200 milligrams per deciliter (mg/dL) — 11.1 millimoles per liter (mmol/L) — or higher suggests diabetes.

diagnosis of diabetes mellitus-glucometer

Interpretation of Random plasma glucose (RPG) values in diagnosis of diabetes mellitus.

 Less than 140 mg/dL


Between 140-199 mg/dL


 200 or higher mg/dL


Once the diagnosis of diabetes is made by random plasma glucose test doctor will advice you to do other tests such as Fasting blood sugar test or oral glucose tolerance test to confirm the diagnosis.

Fasting Plasma Glucose (FPG) Test


  • Overnight fast of atleast 8 hours is required for this test.
  • Fasting means having nothing to eat or drink except sips of water.
  • Blood sample is preferably taken in the morning after an overnight fast

This test is used to detect diabetes.

Interpretation of fasting plasma glucose (FPG) values in diagnosis of diabetes mellitus.

Less than 100 mg/dL


Between 100-125 mg/dL


126 mg/dL or higher


  • If the fasting glucose level is between 100 to 125 mg/dL, then it is a form of prediabetes called as impaired fasting glucose (IFG), which means that you are more likely to develop type 2 diabetes but do not have it yet.
  • If it’s 126 mg/dL (7 mmol/L) or higher on two separate tests, you have diabetes

Oral Glucose Tolerance Test (OGTT)

  • Measures your blood sugar after you have gone at least eight hours without eating and two hours after you drink a glucose-containing beverage.
  • This test can be used to diagnose diabetes or prediabetes.


  • – Patient is required to be overnight fasting for this test.
  • – Three samples are taken.
  • – One fasting sample is taken that is before drinking the glucose.
  • – Then patient is given glucose or sugary liquid to drink and blood sample is taken at 2hour and 3 hour after the drink.
  • This test can be used to diagnose diabetes or prediabetes.
  • The OGTT is more sensitive than the FPG test for diagnosing prediabetes.
  • Unlike fasting blood glucose OGTT  more expensive and it is less convenient to administer.

Interpretation of OGTT values at 2 hours in diagnosis of diabetes mellitus.

139 mg/dl  and below


140 to 199  mg/dl 

(impaired glucose tolerance)

200 mg/dl  and above


  • If  blood sugar level is between 140 and 199 mg/dL 2 hours after drinking the liquid, then it is  a form of prediabetes called impaired glucose tolerance or IGT, meaning that the person is  more likely to develop type 2 diabetes but do not have it yet.
  • A two-hour glucose level of 200 mg/dL or above, then diabetes confirmed by repeating the test on another day.

Gestational diabetes.

Screening test for gestational diabetes.

low risk: absence of risk factors ->>> blood glucose testing is not  be routinely required.

  • Average risk individual: these are the patients who have some risk factors->>> so perform screening test like glucose challenge test for gestational diabetes sometime during the second trimester —that is between 24 and 28 weeks of pregnancy.


High  risk: example (a)  if patient was diagnosed to have gestational diabetes in her previous pregnancy

(b) if patient has any of her parents or siblings having diabetes

(c) if  she is  overweight or obese

etc ->>>  do the test as soon as possible. (mostly at your first prenatal visit)

To know more about the high risk factors for diabetes please do check our blog on risk factors for diabetes mellitus and gestational diabetes 2020

Following are the  screening tests used to screen for gestational diabetes mellitus or GDM:

• Glucose challenge test.

A pregnant female when she visits a doctor for her antenatal clinic the first screening test that he will advice is glucose challenge test. 

This test is also called as glucose screening test.


  • – No overnight fasting required for this test.
  • – First step is to give the patient 50gms of glucose solution to drink.
  • – Blood sample is taken 1 hour after the glucose administration.

A plasma glucose  level  of 140 mg/dL (7.8 mmol/L).


A whole blood glucose level of 130 mg/dl is considered as the cutoff.

If the values of glucose challenge test are more than the cutoff value it means that the patient has a high risk to develop gestational diabetes.

So the doctor will advice for follow up glucose tolerance test to check for gestational diabetes.

• Follow-up glucose tolerance test.

  • Oral glucose tolerance test also called OGTT is used for follow up.


  • – This test requires an overnight fasting of more than 8 hours.
  • – Total 4 blood samples are taken.
  • – First of all a fasting blood sample is taken.
  • – Then patient is given a glucose solution to drink.
  • – This solution contains 100gms of glucose, which is higher than that of the glucose in glucose challenge test.
  • – Now the blood is withdrawn and checked every hourly for next 3 hours.
  • – Total of four samples are taken:
  1. Fasting blood sample.
  2. Blood sample at 1 hour post glucose administration.
  3. Then next sample at 2 hours post glucose administration.
  4. Last sample at 3 hours after giving glucose.

If at least two of the plasma glucose  values are higher than the normal values you’ll be diagnosed with gestational diabetes.

Interpretation of the results of follow up glucose tolerance test in diagnosis of diabetes mellitus.

[criteria for diagnosis of gestational diabetes with 100gms of glucose also known as Carpenter and Coustan criteria]


95 or higher

At 1 hour

180 or higher

At 2 hours

155 or higher

At 3 hours

140 or higher

For more articles on diabetes-types of diabetes mellitus

For more articles on diabetes-prevention of diabetes mellitus

to know about complication of diabetes mellitus.

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