Test Code GT2HR Glucose Tolerance Test (OGTT) LAB169
Test Method
Timed Endpoint; Beckman DXC600
Specimen Requirement
0.5 mL serum or plasma is required.
Additional Specimen Collection Information
Collect blood in lithium heparin green-top or red-top tube
from
a fasting patient. PST and SST (gel tubes) are acceptable. The
fasting specimen is assayed prior to the patient consuming the
glucose drink. If the fasting result is acceptable the patient
is
given the appropriate quantity of glucose drink.
500 mcL of serum or lithium heparin plasma collected at
specified time intervals after the patient has consumed 100 gm
of
glucose drink. Samples with ≥ 3+ lipemia must be cleared
prior to analysis. The serum or plasma must be physically
separated
from the cells within 2 hours of collection.
- Fasting specimen must be tested and less than 126 mg/dl
before
the glucose drink is given. - If the fasting glucose is ≥ 126 mg/dL contact the
ordering physician before continuing the tolerance test. - If the physician is not available contact a pathologist
before
proceeding. - The patient should have had at least 3 days of unrestricted
diet and normal physical activity. - Instruct the patient to remain seated or reclined
throughout
the procedure. - The patient may have water to drink but nothing else.
Coffee
and smoking materials are prohibited. - Children under 16 years will be given a glucose load based
upon
their actual body weight. Include information regarding child’s
weight when requesting the test. - The test is administered in the morning following a fast of
between 8-10 hours. - The NIH (National Institute of Health) recommends a 2
hour
procedure with blood collected at fasting and 2 hours; (3 hour
procedure in pregnant subjects, with an additional specimen
collected at the first and third hour. See Glucose Tolerance
Gestational.) - A physician can request a longer OGTT (Oral Glucose
Tolerance
Test) with different dosages and specimen collection intervals.
Consult a pathologist when this is ordered.
Reference Values
Normal Results:
Adults (nonpregnant)
Fasting: < 100 mg/dL
2 hour: < 140 mg/dL
OGTT diagnostic criteria: (American Diabetes Association; 1999)
Adults (nonpregnant) with diabetes
mellitus:
Fasting: ≥ 126
mg/dL on more than one occasion
2 hour: ≥ 200
mg/dL
Adults (nonpregnant) with impaired glucose
tolerance:
Fasting: ≥ 100
and
< 126 mg/dL
2 hour: ≥ 140
and
< 200 mg/dL
Pregnant subjects with gestational diabetes
must
meet 2 or more of the following criteria:
Fasting: ≥ 95
mg/dL
1 hour: ≥ 180
mg/dL
2 hour: ≥ 155
mg/dL
3 hour: ≥ 140
mg/dL
Critical Value: < 50 mg/dL and > 450 mg/dL
Performance
Testing is performed Monday through Friday.
Same day turn around time.
Useful For
Diagnosis of Diabetes Melitis
LOINC Code Information
72171-2 Glucose Tolerance 2 Hours Panel-Serum Or Plasma
CPT Code Information
82951 Chemistry: Glucose Testing tolerance (GTT), 3
specimens
(includes glucose)