There are various ways to diagnose type 1 diabetes. The testing should usually be carried out in a doctor’s office or a lab. If your doctor feels that your blood sugar level is very high, or you have classic symptoms of high blood sugar, in addition to one positive test, he/she may not need a second test to diagnose diabetes.

The American Diabetes Association (ADA) has recommended the following diagnostic tests for type 1 diabetes:

Glycated Hemoglobin (A1C) Test

The glycated hemoglobin (the oxygen-carrying protein in red blood cells) test gives us an idea about average blood sugar level for the past 2–3 months. It involves measurement of the percentage of blood sugar attached to the hemoglobin molecules. If the sugar levels of blood are high, more hemoglobin molecules will have sugar attached to them.2

Understanding the readings of the test

Result A1C
Normal less than 5.7% 
Prediabetes 5.7% to 6.4%
Diabetes 6.5% or higher

Fasting Plasma Glucose or Fasting Blood Sugar Test

This test gives you a reading of your fasting blood sugar. Fasting, for this test, means that you are not supposed to consume any food or drink (water is allowed) for at least 8 hours prior to this test. It is preferable to get this test done first thing in the morning (before breakfast).1

Understanding the readings of the test

Result Fasting Plasma Glucose
Normal less than 100 mg/dl 
Prediabetes 100 mg/dl to 125 mg/dl
Diabetes 126 mg/dl or higher

Oral Glucose Tolerance Test (OGTT)

The oral glucose tolerance test refers to a 2-hour test that gives you readings of the blood sugar levels 2 hours post consumption of a special sweet drink. This test helps the doctors analyze how your body is processing glucose.1

Understanding the readings of the test

Result Oral Glucose Tolerance Test (OGTT)
Normal less than 140 mg/dl  
Prediabetes 140 mg/dl to 199 mg/dl
Diabetes more than equal to 200 mg/dl

Random Plasma Glucose Tests

As the name suggests, this test is usually advised by a physician on a random basis, especially when an individual has severe symptoms that appear related to diabetes.1

A level of blood glucose ≥ 200 mg/dL indicates that the patient has type 1 diabetes.1

Additionally, the doctors may also advise certain blood tests to detect the presence of autoantibodies those are common to type 1 diabetes. Such tests play a key role in differentiating type 1 diabetes and type 2 diabetes when the physician is unsure of the diagnosis. Also, the appearance of ketones (by-products arising from the breakdown of fats) in urine is highly suggestive of type 1 diabetes.2

Once an individual is diagnosed with type 1 diabetes, he has to be very vigilant about his health and visit the doctor regularly. The hemoglobin A1C test is certainly a better indicator of how well the diabetes treatment plan is working for an individual than the regular blood sugar tests. If the hemoglobin A1C level shows a rise, the physician might consider a change in the insulin regimen, meal plan, or both.2

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