Laboratory tests for diagnosis of diabetes mellitus are the same for diabetes type 1 and type 2. The difference is the reason why your doctor gets you screened for both these types of diabetes.

The symptoms of diabetes type 1 onset suddenly and make your doctor suspect diabetes and send you to the laboratory to get you tested for diabetes.

However, if you have diabetes type 2, symptoms may present gradually or may not present immediately or at all. This can cause your diabetes condition to progress and worsen.

You may know about your condition only after the symptoms of the complications set in. So how will your doctor know you have diabetes?

For this reason, to diagnose diabetes type 2 early, the American Diabetes Association has recommended that you undergo screening tests for diabetes. It has laid down certain guidelines for this purpose.

These screening guidelines identify people who are at a higher risk of developing diabetes and recommend that these people be screened every three years if initial reports are normal.

The diagnostic procedures for diabetes use blood and urine samples for testing.

Who should undergo screening for diabetes?

  • Obese or overweight people with a body mass index (BMI) of over 25
  • People with a family history of diabetes
  • People with high blood pressure are at high risk. High blood pressure and diabetes often coexist.
  • People with high cholesterol. Diabetes and high cholesterol often coexist
  • People with heart disease
  • People who live a sedentary lifestyle with not much physical activity.
  • Women with the polycystic ovarian syndrome.
  • Women who have delivered a baby over 9 pounds weight. Women who have diabetes often deliver larger babies.
  • Women with a history of gestational diabetes (diabetes developed during pregnancy)
  • Any person above the age of 45 years

Laboratory Tests to Diagnose Type 1 and Type 2 Diabetes and Prediabetes

The diagnostic criteria for diabetes involve the following laboratory blood tests to detect type 1 and type 2 diabetes and prediabetes. The doctor uses the test results to know if you are diabetic or you are having a prediabetes condition.

1. Glycated hemoglobin test (HbA1C test)

This blood test indicates how well your blood glucose is being controlled. Its result shows your average blood sugar level regulation over the past 2 to 3 months.

This test measures the percentage of blood glucose attached to the hemoglobin in the red blood cells. Hemoglobin is a protein present in the red blood cells of the blood, which carries oxygen to the various parts of the body.

Higher blood glucose levels will indicate more percentage of glucose attached to the hemoglobin.

Interpreting results

  • An A1C level below 5.7 percent: Normal
  • Between 5.7 and 6.4 percent: Indicates prediabetes or an increased risk of diabetes
  • An A1C  level of 6.5 or higher: Indicates diabetes. This is confirmed by a repeat test at some further time.

People who have diabetes and with higher blood sugar levels should do this test every three months to check their blood sugar status.

For diabetics, whose blood sugar is controlled, the test should be done twice a year.

Though the A1C test is used more to diagnose type 2 diabetes, it is also used for the diagnosis of type 1 diabetes.

Other tests are recommended when the A1C test is not available.

The A1C test readings may be inaccurate in the following conditions:

  • during pregnancy when you may have a hemoglobin variant
  • in anemia,
  • high cholesterol levels,
  • kidney disease
  • if you are taking vitamin C and E supplements

2. Random or casual blood test for glucose

This test measures the blood glucose in your blood at a random time, irrespective of the time when you last ate or have not eaten. A reading above 200 mg/dl indicates that you may have diabetes.

3. Fasting blood glucose test (FBG)

This is the most commonly used test to diagnose diabetes. An early morning blood sample is taken and tested for blood glucose. You should be fasting for eight to twelve hours without having had anything to eat or drink, including no beverages.

Normal blood glucose results with this test should be between 70 to 99 mg/dl.

A level between 100 and 125 mg/dl indicates prediabetes, while any reading above 126 mg/dl will indicate diabetes. To confirm your diabetes, this test is repeated again at another time.

4. Oral glucose tolerance test

For this test, the patient should be fasting for eight to twelve hours. When he comes for the test, his fasting blood sample is taken for testing. He is given a sweet sugary drink, which he must drink quickly. This drink is usually 75 gms of glucose mixed in water (100 gms for pregnant women).

Blood samples are taken every half hour for the next two hours.

In a normal person, the blood glucose levels will rise and quickly fall because of the efficient pancreas pushing insulin into the blood to control the blood glucose.

In diabetes, this will not happen and you will find the blood glucose levels to be high.

Normal values with 75 gm of glucose

  • Fasting blood glucose: less than 100 mg/dl
  • After one hour: less than 184 mg/dl
  • After two hours: less than 140 mg/dl

After two hours if the levels are between 140 and 200 mg/dl, you may be having prediabetes. Anything above 200 mg/dl indicates diabetes. A repeat test is done to confirm the presence of diabetes.

In type 1 diabetes, the urine is tested for ketones. These are byproducts when the body uses up fats to use for energy.

This will help to know if the dosage of insulin is correct. It will also help to know if the person has diabetic ketoacidosis, a dangerous condition.