The diagnosis is generally based on symptoms and supported by a lithium level blood level. Blood levels are most useful six to twelve hours after the last dose. The normal blood serum lithium level in those on treatment is between 0.6-1.2 mEq/L. Some blood tubes contain lithium heparin which may result in falsely positive results.
When lithium toxicity is suspected tests may include:
*fingerstick glucose
* serum lithium concentration 
*basic metabolic panel to assess renal function
* serum acetaminophen and salicylate concentrations to rule out other sources of acute ingestion
*urine pregnancy tests to ensure management does not cause abortion
Imaging tests are not helpful.