Beaumont Laboratory - Lab Test Details
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Beaumont Laboratory

Insulin Response, 5 hr. (to GTT)

Insulin Response: GTT, EPIC: LAB5813, SOFT: ITT5H

Instructions

The patient should fast overnight prior to specimen collection.

Specimen Collection Criteria

Collect: One Gold-top SST tube at 0 minutes (Baseline), and 30 minutes, 1 hour, 2 hours, 3 hours, 4 hours, and 5 hours after the ingestion of the 75 g Glucola load.

Physician Office/Drawsite Specimen Preparation

Let each specimen clot 30-60 minutes then immediately centrifuge to separate serum from cells. Transfer serum to plastic aliquot tubes and refrigerate (2-8°C or 36-46°F) immediately. (Minimum Serum: 0.5 mL each specimen)

Preparation for Courier Transport

Transport: Serum aliquot tubes, refrigerated (2-8°C or 36-46°F). (Minimum Serum: 0.5 mL each specimen)

Rejection Criteria

  • Lipemic, icteric, or grossly hemolyzed specimens.
  • Samples left on the clot at room temperature.
  • Samples subjected to repeated freeze/thaw cycles. 

Storage

Specimen Stability for Testing:

Centrifuged SST Tubes and Microtainers® with Separator Gels
Room Temperature (20-26°C or 68-78.8°F): 2 hours
Refrigerated (2-8°C or 36-46°F): Unacceptable
Frozen (-20°C/-4°F or below): Unacceptable

Red-top Tubes and Microtainers® without Separator Gels
Room Temperature (20-26°C or 68-78.8°F): 2 hours
Refrigerated (2-8°C or 36-46°F): Unacceptable
Frozen (-20°C/-4°F or below): Unacceptable

Serum Specimens (Pour-Overs)
Room Temperature (20-26°C or 68-78.8°F): Unacceptable
Refrigerated (2-8°C or 36-46°F): 7 days
Frozen (-20°C/-4°F or below): 3 months

Specimen Storage in Department Prior to Disposal:

Refrigerated (2-8°C or 36-46°F): 7 days

Laboratory

Royal Oak Special Testing Laboratory.

Performed

Monday - Friday.
Results available within 2 business days.

Reference Range

Normal fasting baseline: Less than 34 microIU/mL
Normal response: Following a glucose load, serum insulin levels should peak at 30 minutes or 1 hour, and the sum of the 2 hour and 3 hour insulin levels should be less than 64 microIU/mL.

Test Methodology

This test is typically done in parallel with a glucose tolerance test. A baseline insulin blood sample is drawn (usually in conjunction with a baseline glucose ), a glucose load is given orally and sequential serum insulin samples (and glucose, if ordered) are drawn.

The following insulin levels are required for interpretation of the Insulin Response to GTT: Fasting, 30 minutes or 1 hour, 2 hours, and 3 hours post glucose load.

Interpretation

Insulin is regulated by the blood glucose level. Increased glucose levels stimulate insulin release. Abnormal serum insulin patterns which have blunted or absent responses to glucose load can indicate low carbohydrate and/or management in the absence of pancreatic gland dysfunction. Elevated serum insulin patterns and delayed peak levels can be indicative of hyperinsulinism such as seen in obesity, Type II diabetes mellitus and certain rare forms of peripheral insulin resistance.

Contraindications:

If the patients fasting blood sugar level is 180 mg/dl or greater, a glucose tolerance test for insulin response should not be ordered. This will prevent the unnecessary administration of an oral glucose load to a non-fasting or overtly diabetic patient.

Clinical Utility

This test is useful in determining the insulin response to glucose challenge.

CPT Code

83525.

Test Codes

EPIC: LAB5813, SOFT: ITT5H

Last Updated

02/08/2016

Microtainer® and Vacutainer® are registered trademarks of Becton, Dickinson and Company.
UroVysion® is a registered trademark of Abbott Laboratories. ThinPrep® is a registered trademark of Hologic, Incorporated.

This directory currently reflects information only for specimens collected and/or processed at the Farmington Hills, Grosse Pointe, Royal Oak, and Troy campuses.