How Hyperglycemia Is Diagnosed

In This Article

Hyperglycemia, otherwise known as high blood sugar, can be diagnosed with a blood test such as a fasting blood sugar, a hemoglobin A1C test, or a fructosamine test. Additionally, hyperglycemia can be determined using a glucose monitor or by drinking a beverage and monitoring the body's glucose response, a test referred to as a glucose tolerance test.

To confirm a diabetes diagnosis, a doctor should conduct two different tests. Your doctor will explain the results and what they mean.

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Self-Checks/At-Home Testing 

If you have diabetes, frequent blood glucose monitoring can help you manage your blood sugars and prevent/detect hyperglycemia. Testing your blood sugar in the morning before you've eaten, two hours after a meal, and before bed can help you understand what causes your blood sugar to rise and how much.

Your medical team will provide you with individualized blood sugar targets based on a variety of factors such as age, length of diagnosis, activity level, weight, and your overall health history.

Generally speaking, hyperglycemia for most non-pregnant adults is defined as:

  • Fasting: Blood glucose reading higher than 130 mg/dL
  • Two hours after a meal: over >180 mg/dL
  • Random blood sugar test: over >200 mg/dL

If you have a random blood sugar that is above normal, there is no reason to panic, especially if you know the cause. Perhaps you ate a little too much carbohydrate at dinner or underestimated your insulin needs. It makes sense to call your health care provider if you notice a pattern of elevated blood sugars. For example, if your blood sugar is higher than 130 mg/dL after an eight hour fast multiple days in a row, you may need to adjust your meal plan, medicines, or activity, and your medical team can help you to do that.

Note that blood sugar checks can yield inaccurate results if you do not have clean, washed hands or if your test strips are expired or have been exposed to extreme temperatures.

If you do not have diabetes but have risk factors such as prediabetes, obesity, a family history of diabetes or you are experiencing symptoms including increased thirst, increased hunger, and increased urination, schedule an appointment to get screened so that you can determine whether or not your blood sugar is elevated.

Labs and Tests

Fasting Blood Glucose Test

The fasting plasma glucose (FPG) test, also known as the fasting blood glucose test (FBG) or fasting blood sugar test, measures blood sugar levels and is used to diagnose diabetes and impaired glucose tolerance. It can also help those people with diabetes to detect hyperglycemia.

The American Diabetes Association (ADA) recommends this test as a screening test for diabetes for those people over age 45. If the results are normal, it is repeated every three years. The FBG test is also recommended if you have had symptoms of diabetes or multiple risk factors for diabetes.

The test consists of a simple, noninvasive blood sample. And for those people with diabetes who check their blood sugars regularly, you can test your own fasting blood sugar using a glucometer. Prior to testing, you must fast—avoid eating or drinking for at least eight hours. Because of this fast, the test is usually done in the morning.

For those people without diabetes, hyperglycemia is indicated when: 

  • A reading of 100 mg/dL to 126 mg/dL suggests impaired glucose tolerance or prediabetes, indicating an increased risk of developing full-blown diabetes.
  • A reading above 126 mg/dL is the threshold at which diabetes is diagnosed. Typically this must be confirmed twice or cross-checked with another diagnostic test.

For those people with diabetes, hyperglycemia is indicated when: 

  • A reading of over 130 mg/dL that occurs a few consecutive days can indicate a pattern of high morning blood sugar.

Hemoglobin A1C Test 

The A1C test (also known as HbA1C, hemoglobin A1c, glycated hemoglobin or glycosylated hemoglobin) is a good general measure of diabetes care and can help to determine hyperglycemia in people with diabetes as well as to diagnose diabetes. The A1C levels indicate a person’s average blood glucose level over the past two-to-three months.

You can retrieve an A1C reading through a regular blood draw. Additionally, many doctors' offices have A1C testing machines which enable them to retrieve the result using a small drop of blood obtained by pricking your finger with a lancet. No fasting is required during this test.

For a person without diabetes, a typical A1C level is about 5 percent. A borderline A1C that indicates hyperglycemia or prediabetes falls within the range of 5.7-6.4 percent.

For those people who have diabetes, the ADA recommends an A1C target of less than or equal to 7 percent and the American Association of Clinical Endocrinologists recommends a level of 6.5 percent or below. However, the ADA also emphasizes that A1C goals should be individualized.

It's important for those people with diabetes to understand what there A1C target is and what value indicates hyperglycemia. Most of the time, when blood sugar control is good, an A1C test is done twice a year. However, for those people who have hyperglycemia, the level may be checked more frequently, especially if medication changes have been made.

Fructosamine Test

The fructosamine test is another blood test, similar to the hemoglobin A1C test, that measures blood glucose levels over the course of two to three weeks. It measures glycated protein in the blood and is typically used to measure blood sugar in those people who have sickle cell anemia or other hemoglobin variants.

Unlike the A1C test, the fructosamine test is not used as a screening test for people who do not have diabetes or who have well-controlled diabetes.

The fructosamine test can be used in addition to blood glucose logging when you've had a recent change in your medicines or insulin and can help to monitor the effectiveness of the new treatments after just a few weeks rather than waiting months to do an A1C test.

Lastly, the fructosamine test is used in gestational diabetes because changes can happen very quickly during pregnancy. The shorter time span of the test allows the doctor to track your blood glucose levels more closely. It can help to manage hyperglycemia more closely and frequently than an A1C test.

Hyperglycemia is indicated when: 

  • For people without diabetes, the fructosamine range is: 175 to 280 mmol/L
  • For people with controlled diabetes, the fructosamine range is: 210 to 421 mmol/L
  • For people with uncontrolled diabetes, the fructosamine range is: 268 to 870 mmol/L

Oral Glucose Tolerance Test

The oral glucose tolerance test (OGTT), also referred to as the glucose tolerance test, measures the body’s ability to metabolize glucose or clear it out of the bloodstream. The test can be used to diagnose diabetes, gestational diabetes (diabetes during pregnancy), or prediabetes (a condition characterized by higher-than-normal blood sugar levels that can lead to type 2 diabetes). The OGTT test is typically not indicated in diagnosing hyperglycemia in those people who already have diabetes.

All pregnant women must undergo a glucose challenge between 24 to 28 weeks gestation. It can either be a 75 gram, 2-hour OGTT or a two-step, 50 gram OGTT, followed by a 100-gram OGTT (pending on the first test result).

The OGTT is also used four to 12 weeks postpartum in women who've had a history of gestational diabetes, in order to confirm persistent diabetes. Additionally, a doctor may recommend an OGTT if he suspects diabetes in cases where a patient’s fasting blood glucose level is normal.

Compared to the FBG test, the OGTT test is more time-consuming. According to the ADA, the OGTT test is the preferred test used in diagnosing type 2 diabetes in adolescents and children. 

The test begins after an eight to 12 hour fast. Next, blood is drawn to establish a fasting glucose level. Following the blood draw, you'll be asked to drink a sugary (glucose-rich) beverage which typically contains 75 grams of carbohydrate. Blood will be drawn at various intervals to measure glucose levels, usually one hour and two hours after the beverage is consumed.

The test reveals how your body metabolized sugar and if it is clearing it out of the blood efficiently. The normal rate of glucose clearing depends on the amount of glucose ingested. After fasting, the normal blood glucose rate is 60 to 100 mg/dL (milligrams per deciliter).

For 75 grams of glucose, normal blood glucose values (for those who are not pregnant) are:

  • After 1 hour: less than 200 mg/dL
  • After 2 hours: less than 140 mg/dL. Between 140 to 199 mg/dL indicates impaired glucose tolerance (prediabetes). If test results are in this range, a patient is at an increased risk of developing diabetes. Greater than 200 mg/dL indicates diabetes.

For 75 grams of glucose, normal blood glucose values (for those who are pregnant) are:

  • Fasting: less than 92 mg/dL
  • After 1 hour: less than 180 mg/dL
  • After 2 hours: 153 mg/dL 

The diagnosis of gestational diabetes mellitus is made when any of the following plasma glucose values are met or exceeded:

Differential Diagnosis

In the event that one of the tests you've had confirms hyperglycemia, you'll likely need another test to determine whether or not you have diabetes, prediabetes, insulin resistance, or some sort of glucose intolerance.

The good news is that detecting hyperglycemia early can increase your chance of preventing diabetes. Most of the time, the treatment is a lifestyle change such as a modified carbohydrate diet, an increase in exercise, and weight loss.

If blood sugars are very high at diagnosis, you may need to start oral medications or insulin. If you have diabetes and your blood sugars are high then you will likely need a change to your treatment plan.

If you are pregnant and fail your first glucose tolerance test, you'll definitely need to take another one. Sometimes women don't pass the first one but pass the second. 

In the event that you have had a regular check-up and your fasting blood sugar comes out to be high, the result can be skewed if you did not fast. Candy, gum, even cough syrup can cause your blood sugar to be elevated, so make sure you tell your health care providers if you haven't truly fasted. 

And if your blood glucose monitoring indicates that your blood sugar is high at certain times of the day, contact your health care provider to see if you need a treatment plan adjustment. 

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Article Sources
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  6. American Diabetes Association. Understanding A1C

  7. Joslin Diabetes Center. Home Blood Glucose (Sugar) Monitoring, Hemoglobin A1c Testing, and Fructosamine Tests

  8. Johns Hopkins Medicine. Alternative markers of glycemia: fructosamine, glycated albumin, 1,5-AG. January 2014.

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Additional Reading
  • American Diabetes Association. Standards of Medical Care in Diabetes-2020. Diabetes Care. 2020;43(Suppl 1).

  • Ayyappan S, Philips S, Kumar CK, Vaithiyanandane V, Sasikala C. Serum fructosamine a better indicator than glycated hemoglobin for monitoring gestational diabetes mellitus. Journal of Pharmacy & Bioallied Sciences. 2015;7(Suppl 1):S32-S34. doi:10.4103/0975-7406.155786.