The Role of Continuous Glucose Monitoring for Detecting Asymptomatic Nocturnal Hypoglycemia and Differentiating Between Different Causes for Morning Hyperglycemia

Issue: 1/2017

Author: Boyadzhieva, Mila B.1 , Hadzhieva, Elitsa G.1 , Hristozov, Kiril H.1 , Georgieva-Hristova, Darina K.2
1 Clinic of Endocrinology, UMHAT “Sv. Marina”, Medical University, Varna
2 Clinic of Neurology, UMHAT “Sv. Marina”, Medical University, Varna


Morning hyperglycemia in diabetic patients is often an obstacle in diagnosis and treatment when analyzing the possible causes: dawn phenomenon, Somogyi effect or just poor glycemic control. Measuring blood glucose (BG) levels in several nights between 3 a.m. and 5 a.m. or using a continuous glucose monitoring system (CGM) is useful in order to correctly diagnose these phenomena.
The aim of the study is to demonstrate how useful CGM is in differentiating between different causes for morning hyperglycemia (BG 10 mmol/l) and to evaluate the frequency of rebound hyperglycemia following asymptomatic nocturnal hypoglycemia (Somogyi effect) among type 1 diabetic patients.
Materials and methods: 19 outpatients with T1DM (15 women and 4 males) with mean age 37,32 ± 13,17 years, mean HbA1c value of 7,18±1,16% and divergent values of self-monitoring fasting BG were included in the study. CGM was performed for the period of 5-7 days using the retrospective iPro 2 system (Medtronic). Morning fasting sensor glucose (SG) readings have been analyzed in respect of nocturnal glycemic control. Nocturnal hypoglycemia was defined as SG < 3,9 mmol/l.
Results: There are 26 nights with hypoglycemia (in 12 out of 19 patients) among the total of 121 nights observed. Fasting SG 10 mmol/l is registered in 28,93% of all nights monitored, nevertheless in just 11,43% it was preceded by nocturnal hypoglycemia. In 84,62% of all nights with hypoglycemia fasting SG is <10 mmol/l, while in 57,69% it is even <5 mmol/l. A significantly lower mean fasting SG is observed after asymptomatic nocturnal hypoglycemia in comparison with that after a night without hypoglycemia (5,98 ± 4,55 mmol/l vs 9,29 ± 4,22 mmol/l, resp., р=0,0007). Morning SG after asymptomatic nocturnal hypoglycemia is not associated with the other glucose values measured during the night (SG in 22:00, 0:00 and 03:00 o’clock) as well as with the hypoglycemic duration (p>0,05).
Conclusion: The CGM data reveal that fasting hyperglycemia 10 mmol/l most often represents the dawn phenomenon or just the poor glycemic control of the patients so far observed. Morning SG after asymptomatic nocturnal hypoglycemia is not associated with the other glucose values measured during the night as well as with the hypoglycemic duration. This proves furthermore the role of CGM to detect no

Key word: nocturnal hypoglycemia, fasting blood glucose, continuous glucose monitoring, Somogyi effect

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