Objective: To use the Continuous Glucose Monitoring System (CGMS, MiniMed, Sylmar, Calif) to determine if bedtime blood glucose levels were associated with the occurrence of nocturnal hypoglycemia.
Study design: Patients (n = 47, 18 boys, mean age 11.8 +/- 4.6 years) with type 1 diabetes used CGMS for 167 nights. Data were analyzed for glucose </=40 or </=50 mg/dL, comparing bedtime blood glucose levels of </=100 or >100 mg/dL and </=150 or >150 mg/dL.
Results: A glucose value of </=40 mg/dL occurred on 27% of nights and </=50 mg/dL on 35% of nights. There was a 2-fold increase (45% vs 22%, P =.015) in the incidence of hypoglycemia with a bedtime glucose </=100 mg/dL and a 1.7-fold increase (46% vs 26%, P =.01) with a value of </=150 mg/dL; most episodes occurred between 9 PM and 1 AM. There was no difference in hypoglycemia duration (86.4 minutes for glucose </=100 mg/dL vs 84.5 minutes for >100 mg/dL, P = NS), and no bedtime glucose value between 110 and 300 mg/dL decreased the incidence of nocturnal hypoglycemia to </=10%. The incidence of nocturnal hypoglycemia was similar for patients using insulin pump and injection therapy, and there was no correlation between hemoglobin A1c and incidence or duration of hypoglycemia.
Conclusions: Nocturnal hypoglycemia is frequent, of long duration, associated with bedtime glucose values </=100 to 150 mg/dL, and predominately in the early part of the night. CGMS is a useful tool to diagnose asymptomatic nocturnal hypoglycemia.