Hey, 

I once checked blood glucose of NOD SCID females (roughly 30 weeks old) after 48h and 72h of a super low caloric diet (a fasting mimicking diet) and the blood glucose was in all three subjects 50-60mg/dl.

It also has been published that fasting of up to 72h (in 30w old mice if I remember right) should lower the blood glucose to a maximum of 50mg/dL. 

loook it up here:

Changhan Lee et al; Cancer Res. 2010 February 15; 70(4): 1564–1572.

so this seems a bit low after only 16h. Did you fast over day or night ?  as mice have rather a contrary circadian rythmn than humans so much mor active during the night and therefore 16h over nighth might have the same effect than 24h...but still it is low