Generally clinical diagnosis
For high-risk patients (pregnancy, children, older adults w/ cardiovascular issues), rule out peritonitis, UTI, and rhabdomyolysis
CBC
Creatinine phosphokinase
Lactic acid
UA
CBC
Creatinine phosphokinase
Lactic acid
UA
Black widow spider bite
Hymenoptera stings 
Octopus bite
Mammalian bites
Armed spider bite
Closed fist infection 
Funnel-web spider bite
Dog bite