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Test Code LAB4098 GTT, 2 HOUR

Specimen Type

Preferred Specimen: Lithium Heparin Plasma (Mint Green Top, Dark Green Top)
Alternative Specimen: Serum (SST, Gold, Corvac, Tiger, Red Top Tube) Sodium Flouride (Gray Top Tube)

Collection Instructions

Draw fasting specimen just prior to 75 gram glucose load. Draw another specimen after 2 hours. Clearly label each specimen.

 

For GTT 2 HOURS, the 1 Hr is only reflexed if test is being used to diagnose GDM. For these specimens, a fasting, 1 Hr, and 2 Hr will need to be drawn. 

Specimen Volume

2 mL each specimen

Minimum Volume

0.3 mL each specimen

Turnaround Time

STAT: 1 hour after receiving all specimens
Routine: 4 hours

Test Schedule

Daily

Sample Stability

3 days if separated from the cells within 30 minutes of collection

Method

Hexokinase

Reference Ranges

Diabetes Mellitus (DM) screening:

  • Fasting 65-99 mg/dL
  • 2 hour < 200 mg/dL
  • A 2 hour glucose result of ≥200 mg/dL indicates diabetes if value is obtained during a 2 hour (75 gram) ADA glucose tolerance testing protocol for type 2 diabetes in nonpregnant adults.

Gestational Diabetes Mellitus (GDM) screening:

  • Fasting < 92 mg/dL 
  • 1 hour < 180 mg/dL
  • 2 hour < 153 mg/dL
  • The diagnosis of Gestational Diabetes Mellitus (GDM) is met when any of the following criteria are met or exceeded.
  • These threshold values apply to blood glucose levels (measured fasting, 1 and 2 hours) after 75 gram oral glucose load. These criteria apply to women at 24-28 weeks of gestation not previously diagnosed with diabetes. 

Test Components

Glucose, fasting, mg/dL

Glucose, 120 minutes, mg/dL

CPT Codes

82950

Patient Prep

This test should be done in the morning after an overnight fast of between 8 and 14 hours, and after at least 3 days of unrestricted diet (150 or more grams carbohydrate per day) and unlimited physical activity. The patient should remain seated and should not smoke throughout the test. Patient can have nothing by mouth except water during test period. GLUCOSE DOSE: Non-pregnant adults-75 grams, children-1.75 gm/kg of ideal body weight up to a maximum of 75 grams.

Glucola doses for 2 HR Glcose Tolerance in Children

Weight in Pounds mls of Glucola containing 75G /296mLs mls of Glucola containing 100G /296mLs Weight in Pounds mls of Glucola containing 75G /296mLs mls of Glucola containg 100G /296mLs
 
 
40 126 94 68 214 160
41 129 97 69 217 162
42 132 99 70 220 165
43 135 101 71 223 167
44 138 104 72 226 170
45 141 106 73 229 172
46 145 108 74 233 174
47 148 111 75 236 177
48 151 113 76 239 179
49 154 115 77 242 181
50 157 118 78 245 184
51 160 120 79 248 186
52 163 122 80 251 188
53 167 125 81 255 191
54 170 127 82 258 193
55 173 130 83 261 195
56 176 132 84 264 198
57 179 134 85 267 200
58 182 137 86 270 202
59 185 139 87 273 205
60 189 141 88 277 207
61 192 144 89 280 210
62 195 146 90 283 212
63 198 148 91 286 214
64 201 151 92 289 217
65 204 153 93 292 219
66 207 155 94 295 221
67 211 158 >95 296 222