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Diagnosis of Diabetes

Diagnosis of Diabetes

ON THIS PAGE
HOW IS DIABETES DIAGNOSED?
FASTING PLASMA GLUCOSE TEST
ORAL GLUCOSE TOLERANCE TEST
RANDOM PLASMA GLUCOSE TEST
ON THIS PAGE
HOW IS DIABETES DIAGNOSED?  |  FASTING PLASMA GLUCOSE TEST
ORAL GLUCOSE TOLERANCE TEST  |   RANDOM PLASMA GLUCOSE TEST

Diagnosis of Diabetes

The glucose level in your blood is used to diagnose and manage diabetes. Fasting glucose test, random glucose test, and A1c test are the three tests that can be used to determine your blood glucose level.

Diagnosis of Diabetes and Prediabetes

Diabetes is diagnosed using the tests listed below:

  • Plasma glucose test. After going at least 8 hours without eating, a fasting plasma glucose test measures your blood glucose. This test is used to determine whether or not you have diabetes or prediabetes.
  • Oral glucose tolerance test. After going at least eight hours without eating and two hours after drinking a glucose-containing beverage, an oral glucose tolerance test examines your blood sugar. This test can be used to determine whether or not you have diabetes or prediabetes.
  • Random plasma glucose test. Your doctor analyses your blood sugar in a random plasma glucose test regardless of when you last ate. This test is used to identify diabetes, but not prediabetes, coupled with a review of symptoms.
  • Hemoglobin A1c (HbA1c) test. Fasting is not required for a haemoglobin A1c (HbA1c) test, which can be used to diagnose or confirm prediabetes or diabetes.

The fasting plasma glucose test or the oral glucose tolerance test should be repeated on a different day to confirm positive test results. Your doctor may recommend a zinc transporter 8 autoantibody (ZnT8Ab) test when you’re first diagnosed with diabetes. This blood test, together with other data and test results, can assist identify whether or not a person has type 1 diabetes. The purpose of the ZnT8Ab test is to provide a quick and accurate diagnosis, which can lead to immediate treatment.

Fasting Plasma Glucose (FPG) Test

The FPG is most accurate when completed first thing in the morning. Table 1 shows the results and their meaning. If your fasting glucose level is between 100 and 125 mg/dL, you have impaired fasting glucose (IFG), which means you’re at risk of developing type 2 diabetes but don’t yet have it. You have diabetes if your blood sugar level is 126 mg/dL or higher, as confirmed by repeating the test on another day.
Table 1. Fasting Plasma Glucose Test
Plasma Glucose Result
(mg/dL)
Diagnosis
99 and below Normal
100 to 125 Prediabetes
(impaired fasting glucose)
126 and above Diabetes*
*The test will require repeating on a different day to confirm the results.

Oral Glucose Tolerance Test (OGTT)

The OGTT is more sensitive than the FPG test for identifying prediabetes, according to research, but it is more difficult to administer. You must fast for at least eight hours before taking the OGTT. Immediately before and two hours after drinking a liquid containing 75 grammes of glucose dissolved in water, your plasma glucose is analysed. Table 2 shows the results and what they mean. If your blood sugar level is between 140 and 199 mg/dL two hours after drinking the liquid, you have impaired glucose tolerance, a type of prediabetes that means you are more likely to develop type 2 diabetes but do not yet have it. Diabetes is diagnosed by a two-hour glucose level of 200 mg/dL or higher, which can be verified by repeating the test on another day. Diabetes is diagnosed by a two-hour glucose level of 200 mg/dL or higher, which can be verified by repeating the test on another day.

Table 2. Oral Glucose Tolerance Test

2-Hour Plasma Glucose Result
(mg/dL)
Diagnosis
139 and below Normal
140 to 199 Prediabetes
(impaired glucose tolerance)
200 and above Diabetes*
*The test will require repeating on a different day to confirm the results.
Plasma glucose levels recorded during the OGTT can also be used to identify gestational diabetes. During the test, blood sugar levels are examined four times. You have gestational diabetes if your blood sugar levels are over normal at least twice during the test. The above-normal OGTT findings for gestational diabetes are shown in Table 3.

Table 3. Gestational Diabetes: Above-Normal Results for the Oral Glucose Tolerance Test

When
Plasma Glucose Result
(mg/dL)
Fasting 95 or higher
At 1 hour 180 or higher
At 2 hours 155 or higher
At 3 hours 140 or higher
Note: Some laboratories use other numbers for this test.
For more information on gestational diabetes diagnosis and treatment, see Diabetes UK

Random Plasma Glucose Test

Diabetes can be diagnosed by a random blood glucose level of 200 mg/dL or higher, as well as the presence of the following symptoms:

  • Urination Increases.
  • Thirst increases.
  • Unexplained weight loss

Fatigue, hazy eyesight, increased hunger, and unhealed wounds are among the other symptoms. To confirm the diagnosis of diabetes, your doctor will test your blood glucose level using the FPG or the OGTT on another day.

Hemoglobin A1c is now utilised as a screening tool or diagnostic test for prediabetes and diabetes in newer guidelines (the test is normally used to measure blood glucose control in diabetes patients over several months). Prediabetes is defined as an HbA1c level of 5.7 percent to 6.4 percent, which can be reversed with lifestyle adjustments. Diabetes is diagnosed when the HbA1c level is 6.5 percent or greater.

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