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Glucose Tolerance Test, 3 Specimens (75g)

Test Code


CPT Code(s)



Fasting, 1-Hour, 2-Hour glucose

Patient Preparation

Fasting required. Fasting is defined as no consumption of food or beverage other than water for at least 8 hours before testing.

Preferred Specimen(s)

Three - 1 mL plasma specimens collected in fluoride/oxalate (gray-top) tubes

Minimum Volume

0.5 mL for each specimen

Alternative Specimen(s)

Plasma from fluoride/oxalate (gray-top) tube in a plastic screw-cap vial • Serum (separated from cells immediately) in a plastic screw-cap vial • Spun SST • Plasma from lithium heparin (green-top) tube in a plastic screw-cap vial • Plasma from sodium heparin (green-top) tube in a plastic screw-cap vial

Collection Instructions

Immediately after a fasting specimen is obtained, have patient ingest a 75 g load of glucose. Draw subsequent specimens 1 and 2 hours later. Label each with the specific draw time. Serum and plasma submissions must be separated from cells.

Transport Container

Fluoride/oxalate (gray-top) tubes

Transport Temperature

Room temperature

Specimen Stability

Room temperature: 4 days
Refrigerated: 7 days
Frozen: 28 days

Whole blood (gray-top) tube
Room temperature: 24 hours
Refrigerated: 72 hours
Frozen: Unacceptable

Sodium fluoride plasma
Room temperature: 7 days
Refrigerated: 7 days
Frozen: 28 days

Heparinized plasma
Room temperature: 48 hours
Refrigerated: 7 days
Frozen: 28 days

Reject Criteria

Unspun serum or plasma separator tube (SST® or PST) • Red-top or green-top tube (serum or heparinized plasma not separated from cells) • Anticoagulants other than lithium heparin, sodium heparin or fluoride/oxalate


Spectrophotometry (SP)

Performing Laboratory

Quest Diagnostics - Southwest Region


Glucose levels may be depressed if sample is left on clot for an excessive length of time.

Reference Range(s)

American Diabetes Association
 Diagnostic Criteria for Diabetes Mellitus

Glucose Value (mg/dL)
Interpretation Fasting 1-Hr Tolerance 2- Hr Tolerance
Normal <100 Not established <140
Impaired Fasting 100-125    
Impaired Tolerance     140-199
Diabetes ≥126*   ≥200* 
 *Must be confirmed by testing on a subsequent day.

Clinical Significance

This test is used for the routine diagnosis of diabetes in children and the non-pregnant adult. For pregnant females see test "Glucose Tolerance Test, Gestational, 4 Specimens (100 g)". For appropriate interpretation of this test, the patient must fast overnight and ingest a 75 g load of glucose. Immediately after, a fasting specimen is obtained. For children, the glucose load is 1.75 g/Kg of body weight, up to 75. The diagnosis of diabetes is made if the fasting glucose is ≥126 mg/dL or if the 2-hour specimen is ≥200 mg/dL.

LOINC®' Code(s)

The Result and LOINC information listed below should not be used for electronic interface maintenance with Quest Diagnostics. Please contact the Quest Diagnostics Connectivity Help Desk for more information at 800-697-9302.

NOTE: The codes listed in the table below are not orderable Test Codes.

Result NameLOINC CodeComponent Name
25004200FASTING SPECIMEN1558-6Glucose^post CFst
250076002 HOUR SPECIMEN1518-0Glucose^2H post 75 g glucose PO
25007730COMMENT8251-1Service comment
251075001 HOUR SPECIMEN1507-3Glucose^1H post 75 g glucose PO

Reference ranges are provided as general guidance only. To interpret test results use the reference range in the laboratory report.

The CPT codes provided are based on AMA guidelines and are for informational purposes only. CPT coding is the sole responsibility of the billing party. Please direct any questions regarding coding to the payer being billed.

LOINC assignment is based on a combination of test attributes, including the method used by the performing laboratory. For tests not performed by Quest Diagnostics, codes are assigned by the performing laboratory.

* The tests listed by specialist are a select group of tests offered. For a complete list of Quest Diagnostics tests, please refer to our Directory of Services.