The diagnosis of morning hyperglycaemia consists of nocturnal blood glucose checks.
If the BG is high both at night and in the morning, this is most likely a dawn phenomenon (Reinhardt 2004). In the case of the dawn phenomenon, therefore, BG checks should be carried out at 10 p.m. / 2 a.m. / 4 a.m. (Herold 2020). For more details see Dawn phenomenon.
In the case of morning hyperglycaemia triggered by the Somogyi effect, these checks are recommended between 3 - 4 h (Herold 2020), as the greatest insulin effectiveness is between 0.00 h and 3.00 h (Hien 2007).
In the Somogyi effect, BG can be low at night and elevated in the morning (Reinhardt 2004), but much more often BG is low or normal in the morning. For more details see Somogyi effect.
CGM
The Dawn phenomenon can be masked by a Somogyi effect. Continuous glucose monitoring (CGM) should be used for further differentiation (Kolossa 2014).