Everything You Need to Know About the 3 Hour Glucose Test

The oral glucose tolerance test (OGTT), also known every bit the glucose tolerance test, gauges the trunk'south ability to metabolize sugar (glucose) and clear it from the bloodstream. The test requires yous to potable a syrupy solution afterwards a menses of fasting. A blood sample is then drawn to determine whether yous are metabolizing glucose as yous should be. The OGTT tin can exist used to diagnose diabetes, gestational diabetes (diabetes during pregnancy), or prediabetes (elevated blood carbohydrate predictive of type ii diabetes), among other things. The OGTT can be performed safely in both adults and children.

Illustration by Emily Roberts, Verywell

Purpose of Test

The OGTT evaluates how the torso manages glucose after a meal. Glucose is a type of saccharide produced when the trunk breaks down carbohydrates consumed in nutrient. Some of the glucose will be used for energy; the residual will exist stored for future use.

The amount of glucose in your blood is controlled by the hormones insulin and glucagon. If you have too much, the pancreas secretes insulin to aid cells absorb and shop glucose. If you have besides little, the pancreas secretes glucagon so that stored glucose tin can exist released back into the bloodstream.

Under normal circumstances, the trunk will be able to maintain the ideal rest of blood glucose. However, if whatsoever parts of the system are impaired, glucose can quickly accumulate, leading to high claret sugar (hyperglycemia) and diabetes.

Lack of insulin or insulin resistance causes college than normal levels of glucose in the blood.

The OGTT is a highly sensitive test that tin can detect imbalances that other tests miss. The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) recommends the OGTT for the following purposes:

Screening and diagnosis of prediabetes or impaired glucose tolerance (IGT)
Screening and diagnosis of type ii diabetes
Screening and diagnosis of gestational diabetes

Amid its other uses, the OGTT tin can be ordered to diagnose reactive hypoglycemia (in which blood sugar drops after eating), acromegaly (an overactive pituitary gland), beta prison cell dysfunction (in which insulin is non beingness secreted), and rare disorders affecting saccharide metabolism (such as hereditary fructose intolerance).

Types

The OGTT process can vary considerably based on the goals of the test. The concentration of the oral glucose solution can differ every bit tin can the timing and number of claret draws required. There are even variations in which a low-carbohydrate diet may exist prescribed.

There are two standard variations used for screening and diagnostic purposes:

A two-60 minutes OGTT, comprised of two blood draws, is used to diagnose diabetes/prediabetes in non-meaning adults and children.
A three-hour OGTT, comprised of iv blood draws, is used to screen gestational diabetes.

Pregnancy Recommendations

The American Higher of Obstetricians and Gynecologists (ACOG) recommends the routine screening for gestational diabetes in all significant women betwixt 24 and 28 weeks of gestation.

With that being said, rather than proceeding directly to a three-hour OGTT, healthcare providers volition often recommend a 1-hour glucose claiming starting time, which does non require fasting. The one-hour glucose challenge may be ordered earlier 24 weeks if y'all are obese, have a family unit history of diabetes, are diagnosed with polycystic ovary syndrome (PCOS), or accept experienced gestational diabetes in the past. If the results of the examination are abnormal—with claret glucose values equal to or greater than 140 milligrams per deciliter (mg/dL)—you would be stepped upwards to the full, three-hour OGTT. Some healthcare providers ready the threshold as depression as 130 mg/dL.

Advantages and Disadvantages

The OGTT is far more than sensitive than the fasting plasma glucose test (FPG) and is frequently ordered when diabetes is suspected but the FPG returns a normal result. Its ability to detect early harm means that people with prediabetes can frequently care for their condition with diet and practise rather than drugs.

The OGTT is too the only test that can definitively diagnose IGT.

Despite these advantages, the OGTT has its limitations:

The OGTT is a time-consuming examination, requiring extensive pre-test fasting and a prolonged testing and waiting period.
The test results can exist influenced by stress, illness, or medications.
Claret is less stable after collection, meaning that the results tin can sometimes be skewed as a result of improper handling or storage of the sample.

In terms of accuracy, the OGTT has a sensitivity (the percent of correct positive test results) of between 81 percent and 93 percent. This is far amend than the FGP, which has a sensitivity of between 45 percent and 54 percent.

Risks and Contraindications

The OGTT is a safe and minimally invasive exam that requires two to iv blood draws. Infection is uncommon but may occur.

However, some may have a reaction to the oral glucose solution, most normally nausea or vomiting. If vomiting occurs during testing, the exam may not be completed.

Though you will be monitored and treated appropriately if needed, know that some people experience hypoglycemia during the OGTT.

An OGTT should not be performed if you:

Already take a confirmed diabetes diagnosis
Take an allergy to sugar or dextrose
Are recovering from surgery, trauma, or infection
Are under extreme psychological stress
Have ever experienced hypokalemic paralysis

Before the Exam

If you are sick or take been recently sick, even with something as simple equally a cold, you cannot take the test. If unsure, call the lab or your healthcare provider.

Timing

Considering you accept to get in at the lab in a fasted state, OGTTs are typically scheduled in the morning. You should be prepared to prepare bated 3 to four hours, depending on whether you lot are taking the two-60 minutes or 3-hour test.

Since stress and anxiety tin can affect your blood sugar levels, arrive for your date at to the lowest degree 30 minutes in advance and so that you take time to settle in and relax.

Location

An OGTT can exist performed at a healthcare provider'south office, a dispensary, a hospital, or an independent lab facility.

What to Wearable

Equally claret will need to be fatigued, either vesture short sleeves or a top that allows you to roll upward your sleeves easily

Food and Drink

You lot will need to finish eating and drinking eight to 12 hours before the test (time spent sleeping counts); follow your healthcare provider's advice. You can have the occasional sip of water if desired.

If you fume, you will need to finish the twenty-four hours of your appointment until the examination is consummate. Smoking not only increases insulin output, simply it impairs glucose tolerance and raises blood pressure.

Medications

Be certain to advise your healthcare provider well-nigh any drugs you may exist taking, whether they are prescription, over-the-counter, nutritional, homeopathic, traditional, or recreational. Certain drugs tin can impact blood glucose and may need to be temporarily stopped.

These may include:

Anticonvulsants like Topamax (topiramate) or Depakote (valproate)
Singular antipsychotics like Clozaril (clozapine) or Seroquel (quetiapine)
Corticosteroids like prednisone or Medrol (methylprednisolone)
Diuretics
Quinolone antibiotics like Cipro (ciprofloxacin) or Levaquin (levofloxacin)
Statin drugs like Crestor (rosuvastatin) and Lipitor (atorvastatin)
Salicylates, including aspirin
Tricyclic antidepressants like Anafranil (clomipramine) or Tofranil (imipramine)

You should never stop taking whatever chronic medication without first consulting with your healthcare provider.

What to Bring

In addition to your ID and health insurance cards, you lot may desire to bring something to read since you lot will be sitting for a couple of hours between blood draws. Some people bring headphones and calming music to listen to.

Notwithstanding, avoid video games or anything that may overstimulate you. This is specially true if your kid is being tested. Instead, bring a storybook or toys, or download a video onto your laptop or tablet.

You lot may besides want to bring a protein bar or snacks to eat once you accept finished, specially if you accept a long drive abode.

Price and Health Insurance

The examination may exist covered in part or in full by your health insurance. Prior authorization is usually not required, merely, just to be safe, contact your insurance visitor beforehand to double-check and appraise what your co-pay or coinsurance costs volition exist.

If you are uninsured, shop around for the best price. Independent labs tend to have the best prices compared to healthcare provider'due south offices or hospitals. You lot should also ask if the lab has a patient assistance program that either offers a tiered cost structure or monthly payments. This is especially useful if you await to have ongoing lab tests.

During the Test

Dissimilar a fasting glucose examination, which only evaluates your blood in a fasted country, an OGTT includes both fasted and not-fasted results. The test procedures can vary based on whether yous are an adult, child, or pregnant.

Pre-Test

On the solar day of the test, later signing in and confirming your insurance information, you will be taken to an exam room where your height and weight will be recorded. Your temperature and claret pressure level may also be taken.

At this point, you will exist asked to roll up your sleeve for the blood describe. To do so, the phlebotomist volition place an elastic tourniquet around your upper arm.

Throughout the Test

A vein in either the crook of your arm or wrist will exist selected and cleansed with an antiseptic wipe. A butterfly needle would and then exist inserted and 2 milliliters (mL) of claret would be extracted for the baseline fasting outcome.

Once the needle is removed and the puncture wound is bandaged, you or your child will be given a sugary glucose solution to beverage. The formulation used varies every bit follows:

For the two-hour OGTT in adults: An viii-ounce solution comprised of 75 grams of carbohydrate
For the 2-hour OGTT in children: The dose is calculated at ane.75 grams of sugar per kilogram of weight (1.75 one thousand/kg), with a maximum dose of 75 grams.
For the three-hour OGTT: An eight-ounce solution comprised of 100 grams of saccharide

Upon drinking the solution, you volition render to the reception expanse for the prescribed waiting time; typically, you cannot leave.

If you are an adult or child being tested for diabetes or prediabetes, you will wait for two hours after drinking the solution and return to the examining room for some other blood draw (for a total of ii blood draws).

If yous are being tested for gestational diabetes, blood samples volition be taken one, two, and three hours later on drinking the solution (for a total of four claret samples).

While y'all will be monitored throughout the exam to ensure that your glucose levels don't drop too low, advise the nurse or phlebotomist if you experience any signs of hypoglycemia, including weakness, sweating, anxiety, shakiness, stake skin, hunger, or irregular heartbeat.

In one case the necessary samples are obtained, you can render dwelling house and resume your normal activities and diet. If you are feeling featherbrained or silly, the medical team may ask that you balance a bit before leaving.

After the Test

While side effects are uncommon, some people may experience bloating, nausea, upset tum, and diarrhea as a event of the oral solution. These can often be relieved with an over-the-counter anti-diarrheal, past sipping ginger tea, or chewing peppermint gum. Some may also experience pain, swelling, or bruising at the site of the claret draw.

Call your healthcare provider if you experience whatsoever unusual pain, swelling, or excessive bleeding at the puncture site or have symptoms of infection, including loftier fever, shivering chills, rapid heart rate, rapid breathing, or shortness of breath.

Interpreting the Results

Your healthcare provider should receive the examination results within two to three days. Along with the results will be reference ranges with high and depression numeric values. Annihilation between the loftier and low values is considered normal. Anything exterior of the reference range is either considered abnormally high (often denoted with the letter "H") or abnormally low (denoted with "Fifty").

Two-hr OGTT results for adults or children are interpreted as follows:

Normal: beneath 140 mg/dL
Prediabetes or IGT: 140 and 199 mg/dL
Diabetes (presumed): 200 mg/dL and above

If the claret glucose value is over 200 mg/dL, the healthcare provider will repeat the examination or use another test to confirm the diabetes diagnosis. If both tests are positive, the diagnosis tin can be considered definitive.

3-hour OGTT results are interpreted differently. For this, a preliminary diagnosis is made based on one or more high glucose values during one or more of the iv claret draws. Abnormal values need to be confirmed with a repeat OGTT.

The normal reference ranges for a three-hour OGTT are described as follows:

Normal in a fasted state: Less than 95 mg/dL
Normal later on ane hour: Less than 180 mg/dL
Normal after two hours: Less than 155 mg/dL
Normal later on three hours: Less than 140 mg/dL

If any one of these values is loftier, the test is repeated in four weeks. If, after the 2nd test, two or more values are elevated, gestational diabetes is definitively diagnosed.

Follow-Upwardly

Once you have been definitively diagnosed with diabetes, your healthcare provider will sometimes need to distinguish whether you lot have blazon 1 or type 2 diabetes. Since type one diabetes is an autoimmune disorder in which your immune system attacks insulin-producing beta cells of the pancreas, your healthcare provider can club tests to detect whether yous have autoantibodies associated with the illness. Another test, called a C-peptide test, may exist used.

Irrespective of the type of diabetes you take, your healthcare provider will perform other tests to obtain baseline values past which to monitor disease progression. Chief amid these is the A1C examination, which measures your average blood sugars over the previous three months.

Depending on your baseline results, your healthcare provider may recommend changes in your nutrition and exercise (referred to as medical nutritional therapy, or MNT), and schedule routine blood tests every three to half dozen months.

At other times, your healthcare provider may recommend drug therapies, like metformin or insulin, to better control your blood sugar. The current handling recommendations are as follows:

For prediabetes, metformin is recommended when your fasting claret glucose is between 100 to 125 mg/dL and/or your blood glucose 2 hours afterward a meal is betwixt 140 and 199 mg/dL. Nonetheless, studies have shown that lifestyle modification is the about constructive method in reducing the run a risk of developing into blazon two diabetes.
For type 2 diabetes, metformin is typically the starting time oral drug prescribed to command your blood saccharide. If needed, other classes of drugs (sulfonylureas, meglitinides, thiazolidinediones, DPP-4 inhibitors, and GLP-1 receptor agonists) may be added. Insulin therapy should be started if y'all are on dual oral therapy and your A1C has been over 7 percent for 2 to three months.
For gestational diabetes, ACOG recommends that insulin treatment exist started when your fasting claret glucose exceeds 95 mg/dL and/or your blood glucose ii hours later a meal exceeds 120 mg/dL.

Take fourth dimension to understand your healthcare provider's recommendations and ask whatsoever questions you may take.

Type 2 Diabetes Doctor Discussion Guide

Get our printable guide for your next healthcare provider's appointment to assistance you ask the right questions.

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A Word From Verywell

The OGTT is a valuable test that tin ofttimes confirm diabetes when other tests can't. If yous take symptoms of diabetes but tests fail to provide definitive proof, ask your healthcare provider if the OGTT is an appropriate option.

Co-ordinate to 2017 statistics from the Centers for Disease Command and Prevention, over xxx meg Americans are living with diabetes, and over 84 million take prediabetes. Of these, only 1 in 4 with diabetes are aware of their status, while only one in 9 with prediabetes has been diagnosed.

As such, it important to see a healthcare provider if you experience some or all of the following symptoms:

Increased thirst
Frequent urination
Persistent fatigue
Blurred vision
Frequent infections or sores that are slow to heal
Increased hunger
Unexplained weight loss
Dark patches of velvety pare, commonly effectually the armpits or cervix

Early diagnosis tin can significantly reduce your hazard of diabetes-related illness complications and death.

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Source: https://www.verywellhealth.com/the-oral-glucose-tolerance-test-1087684