A glucose test follows the same general pattern as any other blood test. An elastic band is wrapped around the patient’s upper arm. This temporarily stops the flow of blood through the veins in the arm, keeping veins below the band larger and free from collapse. Veins in this state are more easily punctured by a needle.

The needle site is cleaned with alcohol before the needle is inserted. Occasionally, more than one needle stick may be necessary if the vein does not provide enough blood.

Once the needle is properly placed in the vein, a collection tube is attached and the blood flows into the tube. Once the blood has been captured, the band around the patient’s arm is removed and a gauze pad or cotton ball is placed over the puncture site. Pressure is applied for several minutes until the blood clots.

In addition to blood testing, an oral glucose tolerance test (OGTT) involves the ingestion of glucose and water. Patients ingest glucose before their blood is sampled. In a standard OGTT, the patient will drink between 75 grams and 100 grams of glucose. Pregnant women consume 100 grams of glucose. Blood is drawn at fasting, one hour and two hours after ingesting glucose if patients are being tested for gestational diabetes. Samples are taken one, two and three hours after glucose ingestion for others.

A glucose challenge test also involves drinking a sugary solution, this one containing 50 grams of glucose. Blood is drawn an hour later.

The drinks used in these two tests are extremely sweet and may cause nausea or vomiting in some patients. If vomiting occurs, the test is usually rescheduled for another day.