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Oral Glucose Tolerance Tests for CFRD

An Oral Glucose Tolerance Test (OGTT) is one of the tests that the Cystic Fibrosis Foundation recommends be performed yearly for people age 14 and up. OGTT is ordered when impaired glucose tolerance, hyperglycemia, hypoglycemia, or cystic fibrosis related diabetes (CFRD) is suspected.

Early detection of diabetes helps reduce the likelihood of developing complications of the disease. Signs and symptoms of diabetes may include:

• extreme thirst
• frequent urination, especially at night
• unexplained weight loss
• fatigue and listlessness
• vision changes
• infections or sores that heal too slowly
  

Similarly, hypoglycemia (low blood sugar) can also have complications for cystic fibrosis patients. Symptoms may include:

• sweating
• extreme hunger
• shakiness, hand tremors
• confusion or inability to concentrate
• blurry vision
• calling out in sleep

The procedure requires that the patient fast for 8 to 10 hours the night before the test. An initial blood sample is taken to determine the blood sugar level in a fasting state. Then the patient is given a liquid to drink that has a specific concentration of sugar in it. This is called a “glucose challenge” or “glucose loading.” The glucose challenge drink is extremely sweet, but is usually flavored and chilled to make it taste better.
The patient must then wait 2 hours before having more blood drawn. During this time no food or drink is to be ingested. This ensures an accurate result in the blood test.
Interpreting the results
Fasting

• Normal: 70-99 mg/dL (3.9 to 5.5.mmol/L)
• Impaired Fasting Glucose: 100-125 mg/dL (5.6 to 6.9mmol/L)
• Diabetes: 126 mg/dL and above (7.0mmol/L)

2-hour fasting OGTT

• Normal: >140mg/dL (7.8 mmol/L)
• Impaired Glucose Tolerance: 140-200 mg/dL (7.8 to 11.1 mmol/L)
• Diabetes: >200 mg/dL
  

- Lauren Beyenhof