The intravenous glucose tolerance test (IVGTT) is essentially the same as the OGTT, except that the carbohydrate challenge is administered IV instead of orally. Because the results are somewhat difficult to interpret, the IVGTT is used only in certain clinical situations or for research purposes.

• The reference values are the same as those for the OGTT, except that the blood glucose level at the ½-hour interval may be 300 to 400 mg/dL because of the direct IV administration of the glucose load.

• Those factors that may alter the results of an OGTT may also alter the results of an IVGTT.
• Infusions of total parenteral nutrition (TPN, hyperalimentation) during the test may lead to falsely elevated values; alternative solutions with less glucose should be infused for at least 3 hours before and during the test.

• Inability to take or tolerate oral glucose preparations used for the OGTT
• Suspected gastrointestinal malabsorption problems that interfere with accurate performance of the OGTT
• Evaluation of blood glucose control without the effects of gastrin, secretin, cholecystokinin, and gastric inhibitory peptide, all of which stimulate insulin production after oral ingestion of glucose

Nursing Care Before the Procedure

Client preparation is essentially the same as that for the OGTT.

• If the person is receiving TPN, an alternative solution with less glucose should be prescribed and infused for at least 3 hours before and during the test.

The procedure is essentially the same as that for the OGTT except that an intermittent venous access device (e.g., heparin lock) may be inserted to administer the glucose load and to obtain blood samples. Existing IV lines also may be used to administer the carbohydrate challenge, which is usually 50 percent glucose, with the amount to be given determined by the client's weight or body surface.

Nursing Care After the Procedure

Care and assessment after the procedure are the same as those for the OGTT.

• If an intermittent venous access device was inserted for the procedure, remove it after completion of the test and apply a pressure bandage to the site.
• Resume food and medications withheld before the test, as well as usual activities.
• Resume infusions of TPN as ordered.