A glucose challenge test requires little preparation. Physicians typically do not instruct patients to fast, but may in some cases. They may also recommend withholding certain medications. The test can be performed at a physician’s office or at a laboratory.             

On the day of the test, the procedure will be explained and patients will have the opportunity to ask questions. The medical professional will ask questions about the patient’s medical history before the test, to determine if the patient is taking any medications that will interfere with the test’s accuracy. The patient will also be asked about any medical problems she may have.

The patient will drink 50 grams of a glucose solution within a few minutes. The solution is extremely sweet and may cause nausea or vomiting in some patients. If vomiting occurs, the test is usually rescheduled for another day. An hour after the patient has ingested the glucose solution, blood will be drawn, usually from a vein (venipuncture) from the inside of the elbow or the back of the hand. Sometimes patients are given the solution at a previous medical appointment and keep it at home so they can drink it before the test and avoid the one-hour wait.

First the puncture site is sterilized with antiseptic and an elastic band is wrapped around the patient’s upper arm. As a result, the pressure restricts blood flow through the vein and causes the veins below the band to fill with blood.

A needle is then inserted into a vein. Occasionally more than one puncture is necessary to locate a vein. Some people may feel some discomfort when the needle is inserted, but most feel only a prick or stinging sensation. Once the needle is inserted into a vein, a tube is attached to collect the blood as it begins to flow out. The elastic band is then removed.

The needle is withdrawn after the blood is collected and a small cotton ball is applied with light pressure over the puncture site. After several minutes a small bandage will be placed on the puncture wound. The entire process takes less than 10 minutes. The sample is sent to a laboratory for analysis and results are returned in several days.

Despite the precautions taken to avoid bruising and soreness, it does sometimes occur. Typically, this is not a cause for concern. To minimize soreness, patients may apply a warm compress to the puncture site and repeat the application every three hours until the discoloration or pain subsides.