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glucose challenge (tolerance) test
Indications:
- screen for gestational diabetes
- ref [2] suggests GTT for diagnosis of dysautonomia & small fiber neuropathy in a 44 year old man with normal HgbA1c & fasting plasma glucose
Contraindications:
- generally NOT recommended as a screening test for diabetes mellitus (except in the case of pregnancy) because of cost, incovenience, lack of reproducibility, & occasional patient discomfort
Procedure:
1) fasting serum glucose
a) between 7 & 9 AM
b) after 30 minutes of rest
2) glucose ingestion
a) within 5 minutes of obtaining fasting serum glucose
b) consumed within a 5 minute interval
c) dose
1] adults: 75 g used
2] pediatrics: 1.75 g/kg
3] 50 g used for gestational screening
4] 100 g used for gestational GTT
3) specimens drawn at 1 & 2 hours after glucose ingestion
4) testing for gestational diabetes utilizes specimens drawn at 1,2 & 3 hours after glucose ingestion
Clinical significance:
Abnormal glucose tolerance test:
1) fasting glucose > 115 mg/dL
2) any value of glucose > 200 mg/dL
3) 2 hour glucose > 140 mg/dL
-> a value > 200 mg/dL makes the diagnosis of diabetes mellitus
4) gestational GTT (see gestational diabetes)
a) fasting glucose > 105 mg/dL
b) 1 hour glucose > 190 mg/dL
c) 2 hour glucose > 165 mg/dL
d) 3 hour glucose > 145 mg/dL
Adverse effects:
- higher doses of glucose may cause nausea/vomiting & invalidate results
- see gestational diabetes
Related
diabetes mellitus type 2 (insulin-resistant)
impaired fasting glucose
impaired glucose tolerance
pregnancy (gestation)
Specific
growth hormone (GH) suppression test; glucose challenge test for acromegaly
General
provocative clinical test
chemistry panel
References
- Clinical Diagnosis & Management by Laboratory Methods,
19th edition, J.B. Henry (ed), W.B. Saunders Co.,
Philadelphia, PA. 1996, pg 200-203
- Medical Knowledge Self Assessment Program (MKSAP) 11, 17.
American College of Physicians, Philadelphia 1998, 2015
- Mayo Clinic: Glucose Challenge Test
http://www.mayoclinic.com/health/glucose-challenge-test/MY00146
Components
glucose in serum baseline
glucose in serum post glucose