The “other” designation refers to multiple other specific causes of an elevated blood glucose: pancreatectomy, pancreatitis, non-pancreatic diseases, drug therapy, etc. For a detailed list the reader is referred to the reference Expert Committee, 2003.
Gestational diabetes (GDM) is defined as any abnormality in glucose levels noted for the first time during pregnancy. Gestational diabetes is diagnosed in approximately 7% of all pregnancies in the United States. During pregnancy, the placenta and placental hormones create an insulin resistance that is most pronounced in the last trimester. Risk assessment for diabetes is suggested starting at the first prenatal visit. High-risk women should be screened immediately. Screening may be deferred in lower-risk women until the 24th to 28th week of gestation.
TABLE 41–4 Diagnostic criteria for diabetes.
A. Plasma or Serum Glucose
A plasma glucose level of 126 mg/dL (7 mmol/L) or higher on more than one occasion after at least 8 hours of fasting is diagnostic of diabetes mellitus (Table 41–4). Fasting plasma glucose levels of 100–125 mg/dL (5.6–6.9 mmol/L) are associated with increased risk of diabetes (impaired fasting glucose tolerance).
If the fasting plasma glucose level is less than 126 mg/dL (7 mMol/L) but diabetes is nonetheless suspected, then a standardized oral glucose tolerance test may be done (Table 41–4). The patient should eat nothing after midnight prior to the test day. On the morning of the test, adults are then given 75 g of glucose in 300 mL of water; children are given 1.75 g of glucose per kilogram of ideal body weight. The glucose load is consumed within 5 minutes. Blood samples for plasma glucose are obtained at 0 and 120 minutes after ingestion of glucose. An oral glucose tolerance test is normal if the fasting venous plasma glucose value is less than 100 mg/dL (5.6 mmol/L) and the 2-hour value falls below 140 mg/dL (7.8 mmol/L). A fasting value of 126 mg/dL (7 mmol/L) or higher or a 2-hour value of greater than 200 mg/dL (11.1 mmol/L) is diagnostic of diabetes mellitus. Patients with 2-hour value of 140–199 mg/dL (7.8–11.1 mmol/L) have impaired glucose tolerance.
B. Hemoglobin A1c Measurements
When plasma glucose levels are in the normal range, about 4–6% of hemoglobin A has one or both of the N terminal valines of their beta chains irreversibly glycated by glucose—referred to as hemoglobin A1c (HbA1c). The HbA1c fraction is abnormally elevated in people with diabetes with chronic hyperglycemia. Since red cells have a lifespan of up to 120 days, the HbA1c value reflects plasma glucose levels over the preceding 8–12 weeks. In patients who monitor their glucose levels, the HbA1c value provides a valuable check on the accuracy of their monitoring. In patients who do not monitor their glucose levels, HbA1c measurements are essential for adjusting treatment. HbA1c can be used to diagnose diabetes. An HbA1c of 6.5% or greater if confirmed by repeat testing is diagnostic of diabetes. Less than 5.7% is normal, and patients with levels of 5.7–6.4% are considered at high risk for developing diabetes (Table 41–4).
C. Urine or Blood Ketones