Patients with known diabetes who are not systemically ill and can identify a clear precipitant, no extensive workup is required.
In severely ill patients, consider:
BMP
LFT
EtOH
Infectious workup: CXR, UA, urine and blood cultures
ECG, troponin
Other studies (not normally done in ED): insulin, C-peptide, pro-insulin, glucagon, growth hormone, cortisol, B-OH, insulin antibodies
Exogenous insulin shows suppressed C-peptide levels (artificial insulin does not contain C-peptide)
MEN-1 genetic testing for insulinoma suspicion
Elevated proinsulin and C-peptide during<unk>  episode in context of insulinoma
BMP
LFT
EtOH
Infectious workup: CXR, UA, urine and blood cultures
ECG, troponin
Other studies (not normally done in ED): insulin, C-peptide, pro-insulin, glucagon, growth hormone, cortisol, B-OH, insulin antibodies
Exogenous insulin shows suppressed C-peptide levels (artificial insulin does not contain C-peptide)
MEN-1 genetic testing for insulinoma suspicion
Elevated proinsulin and C-peptide during<unk>  episode in context of insulinoma
Exogenous insulin shows suppressed C-peptide levels (artificial insulin does not contain C-peptide)
MEN-1 genetic testing for insulinoma suspicion
Elevated proinsulin and C-peptide during<unk>  episode in context of insulinoma
"Whipple's Triad"
Symptoms suggestive of<unk> 
See Clinical Features
Low glucose
Serum glucose <60mg/dL
Generally symptomatic at <55mg/dL though threshold is variable depending on chronicity
Resolution of symptoms after administration of glucose
See Clinical Features
Serum glucose <60mg/dL
Generally symptomatic at <55mg/dL though threshold is variable depending on chronicity
Hypoglycemia
Anti-hyperglycemic
Nonketotic hyperglycemia
Insulin
Ketonemia
Oral secretagogue
Hyperammonemia
Sulfonylurea toxicity