Glucose Tolerance, 2 Hour, Plasma or Serum

Test Code

Alias/See Also

CPT Codes

Preferred Specimen
1.0 mL plasma from Green top (Lithium Heparin)

Minimum Volume
0.5 mL

Other Acceptable Specimens
1.0 mL serum from Serum Gel or Red Top

A copy of the Glucose Tolerance Patient Information (English / Spanish) should be given to the outpatient.
  1. Draw blood early in morning from a patient fasting at least 8 hours.
  2. Perform glucose monitor from green-top (LiHep) tube or on a fingerstick specimen before giving patient 75 g GlucolaTM supplied.
  3. For outpatients drawn at an NCMC service center: If fasting glucose monitor or fingerstick glucose is >120 mg/dL, notify North Colorado Medical Center Chemistry Department at 970-810-6412 and forward  fasting tube for a STAT Glucose.  If this value is >120 mg/dL, do not proceed with procedure. Chemistry department will notify a pathologist, and he will contact patient’s physician. Patient will be asked to wait (if outpatient) until physician can be contacted.
  4. For patients drawn at remote clinics:  A fasting glucose monitor or fingerstick glucose is >120 mg/dL is diagnostic of diabetes mellitus. However, finger stick glucose value is not as accurate as confirmatory glucose value from a standard chemistry analyzer. Therefore, dependent on the magnitude of finger stick glucose value, a clinic physician may make the determination as to whether to send a fasting specimen to the laboratory (eg, for a very high finger stick value that is probably diagnostic for DM) or to proceed to 2 hour GTT (eg, a finger stick value that is in the vicinity of 120 mg/dL)
  5. If fasting glucose is <120 mg/dL, proceed as follows:
  6. Instruct patient to drink 300 mL (10 oz. cup) of water. For males and non-pregnant females, administer 75 g of GlucolaTM. Patient must complete ingestion of GlucolaTM within 5 to 10 minutes.
  7. Record the time of the start of GlucolaTM (all timings proceed from this point).
  8. Draw blood at 2 hours after ingestion of 75 g GlucolaTM.
  9. Label tubes with the patient’s full name, fasting or 2 hour, and date and time of collection.
  • If symptoms such as pallor, sweating, fainting, or marked nausea develop during test, procedure should be discontinued and repeated at another time.
  • For further information see Patient Preparation for Glucose Tolerance Testing in Specimen Collection and Preparation.

Specimen Stability
Specimen Type Temperature Time
Plasma Li Hep Refrigerated 72 hours
Serum SST Refrigerated 72 hours
Red Top – Separated* Refrigerated 72 hours
*Centrifuge and aliquot into a plastic vial.

Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)
Gross hemolysis
For NCMC only: Gross lipemia if plasma - Serum specimen needed if Grossly Lipemic.

Hexokinase Bichromatic Endpoint

Setup Schedule
Monday through Sunday; Continuously

Report Available
Same day

Reference Range
Glucose Fasting (GTT): 60-99 mg/dL
Critical value (automatic call-back): <50 or >500 mg/dL
Interpretive Data:
  Normal Impaired Diabetic
Fasting <100 101-125*  ≥125
2 Hour <140  141-199** ≥199
* impaired fasting glucose (IFG)  
** impaired glucose tolerance (IGT)   

Performing Laboratory
Banner Fort Collins Medical Center Laboratory
Mckee Medical Center Laboratory
North Colorado Medical Center Laboratory
Summit View Laboratory
Sterling Regional Medical Center
East Morgan County Hospital

The CPT Codes provided in this document 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 payor being billed. Any Profile/panel component may be ordered separately. Reflex tests are performed at an additional charge.