General
Synonym/Acronym:
Standard oral tolerance test, standard gestational screen, standard gestational tolerance test, GTT.
Common Use:
To evaluate blood glucose levels to assist in diagnosing diseases such as diabetes.
Specimen:
Plasma (1 mL) collected in a gray-top (sodium fluoride) tube. Serum (1 mL) collected in a red- or tiger-top tube or plasma collected in a green-top (heparin) tube is also acceptable, but plasma is recommended for diagnosis. It is important to use the same type of collection container throughout the entire test.
Normal Findings:
(Method: Spectrophotometry)
| Conventional Units | SI Units (Conventional Units × 0.0555) | |
|---|
| Standard Oral Glucose Tolerance (Up to 75-g Glucose Load) |
| Fasting sample | Less than 100 mg/dL | Less than 5.6 mmol/L | |
| Prediabetes or impaired fasting sample | 100–125 mg/dL | 5.6–6.9 mmol/L | |
| 2-hr sample | Less than 200 mg/dL | Less than 11.1 mmol/L | |
| Prediabetes or impaired 2–hr sample | 140–199 mg/dL | 7.8–11 mmol/L | |
| Tolerance Tests for Gestational Diabetes |
| ACOG Standard gestational screen (50-g glucose load) | Less than 141 mg/dL | Less than 7.8 mmol/L | |
| Standard gestational tolerance | ADA Threshold Recommendations for Gestational Diabetes (2012) (75-g glucose load) | ACOG Threshold Recommendations for Gestational Diabetes (2011); either Carpenter and Coustan or National Diabetes Data Group (100-g glucose load) |
| | Carpenter and Coustan | National Diabetes Data Group |
| Fasting sample | Less than 93 mg/dL (SI: Less than 5.2 mmol/L) | Less than 95 mg/dL (SI: Less than 5.3 mmol/L) | Less than 105 mg/dL (SI: Less than 5.8 mmol/L) |
| 1-hr sample | Less than 181 mg/dL (SI: Less than 10 mmol/L) | Less 180 mg/dL (SI: Less than 10 mmol/L) | Less than 190 mg/dL (SI: Less than 10.5 mmol/L) |
| 2-hr sample | Less than 154 mg/dL (SI: Less than 8.5 mmol/L) | Less than 155 mg/dL (SI: Less than 8.5 mmol/L) | Less than 165 mg/dL (SI: Less than 9.2 mmol/L) |
| 3-hr sample | N/A | Less than 140 mg/dL (SI: Less than 7.8 mmol/L) | Less than 145 mg/dL (SI: Less than 8 mmol/L) |
| Plasma glucose values are reported to be 10% to 20% higher than serum values. According to recommendations of the ADA, the diagnosis of gestational diabetes is made if any of the four thresholds are met or exceeded. According to recommendations of the ACOG or National Diabetes Data Group, the diagnosis of gestational diabetes is made if any two of the four thresholds are met or exceeded.ACOG = American Congress of Obstetricians and Gynecologists; ADA = American Diabetes Association. |
Glucose Tolerance Tests has been found in Davis's Lab & Diagnostic Tests
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