Here are definitions of some common terms that will help you understand what your CF doctor is telling you about your CFRD test results. You may want to print this page for reference when you talk with your doctor.
Blood Glucose: The amount of sugar in the blood. If it's too high, it may be diabetes.
CFRD with Fasting Hyperglycemia: A “fasting” blood glucose level of at least 126 mg/dl (7.0 mmol/L) and/or a blood glucose 2 hours after an oral glucose load of at least 200 mg/dl (11.1 mmol/L) during an OGTT. This type of CFRD will likely cause the classic diabetes symptoms and is always treated with insulin.
CFRD Without Fasting Hyperglycemia: A “fasting” blood glucose less than 100 mg/dl (5.6 mmol/L), but when the 2-hour blood glucose after an oral glucose load during an OGTT is at least 200mg/dl (11.1 mmol/L). You may or may not have classic diabetes symptoms with this type of diabetes. This type of CFRD is always treated with insulin.
Fasting Blood Glucose (FBG): A blood glucose level measured after not eating any food or not drinking for 8 hours. Normal FBG is less than 100 mg/dl (5.5mmol/L).
Hemoglobin A1C (HbA1c): This test shows how much sugar is bound or “stuck” to your red blood cells. It shows the average blood sugar level over the last 3 months. While not as accurate to diagnose CFRD as an OGTT, if your HbA1c is 6.5 percent or greater, you have CFRD.
Indeterminate Glucose Tolerance/Indeterminate Glycemia (INDET): A blood glucose level measured in the middle of an OGTT that is at least 200 mg/dl (11.1 mmol/L) in the presence of a normal fasting and 2-hour blood glucose levels. Indeterminate glucose tolerance can also be detected when testing blood glucose with a glucose meter randomly at home or by using a continuous glucose monitor system (CGMS).
Impaired Fasting Glucose (IFG): A fasting blood glucose that is above normal; 100-125 mg/dl, (5.6-6.9 mmol/l).
Impaired Glucose Tolerance (IGT): A fasting blood glucose of 100 mg/dL (5.5 mmol/L) -125 mg/dl (6.9 mmol/L) and/or a blood glucose of 141-199 mg/dL (7.8-11.1 mmol/L) 2 hours after an oral glucose load during an OGTT.
Insulin Insufficiency: When the pancreas doesn’t make enough insulin.
Insulin Resistance: When the pancreas makes insulin, but the cells in the body cannot not absorb the insulin properly; therefore, the blood glucose is high. More insulin is needed to lower blood glucose.
Oral Glucose Tolerance Test (OGTT): This test is used to diagnose not just CFRD but also the different types of abnormal glucose tolerance in CF. You must fast (nothing to eat or drink) for 8 hours. Your blood is then drawn to measure your “fasting” glucose level. You are then asked to drink a glucose-containing beverage. Your blood glucose is measured again 2 hours later. Sometimes, glucose is measured at 1, 2 and 3 hours. If your blood glucose after 2 hours is 200 mg/dl (11.1 mmol/L) or higher, you have CFRD.
Postprandial Glucose Level: Blood glucose level 2 hours after a meal.
Putting the Definitions to Work
Now let’s use some of those definitions to understand the different levels of glucose tolerance that usually lead to CFRD.
Abnormal Glucose Tolerance
Few people with CF have “normal” glucose tolerance. Glucose tolerance abnormalities can be thought of as impaired fasting glucose (IFG) and impaired glucose tolerance (IGT), CFRD without fasting hyperglycemia (CFRD FH-) and CFRD with fasting hyperglycemia (CFRD FH+).
Also, many people have normal fasting and 2-hour blood glucose levels, but they have a high blood glucose in the middle of the OGTT. This is called indeterminate glucose tolerance or indeterminate glycemia (INDET).
Indeterminate glucose tolerance can also be seen when testing blood glucose with a glucose meter randomly at home or by using a continuous glucose monitor system (CGMS).
The meaning of impaired glucose tolerance and indeterminate glucose tolerance in CF is not known. It is common and shows mild abnormal glucose tolerance.
Everyone with abnormal glucose tolerance should have an OGTT every year or have it done earlier if symptoms occur. In children with CF who have not reached puberty, both of these conditions (IGT, INDET) have been linked with CFRD.
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