This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: NEET Jan 2020, Subject name: Pharmacology
A female patient was on lithium therapy for bipolar disorder for 6 months. She kept the fast for few days due to religious reasons and presented with seizures, coarse tremors, confusion and weakness of limbs. Which of the following should be done to diagnose her condition? 
Select and explain. 
A. Serum Electrolytes, B. Serum lithium levels, C. ECG, D. MRI
B: Serum lithium levels
Answer: B: Serum lithium levels 
Explanation: Lithium side effects L - leucocytesLeucocytosis I - Increase T - tremors H - hypothyroidism I - increase Polyuria U - Urine M - avoided in mothers -Plasma concentration norms Acute mania - 0.8 - 1.2 mEq/L Prophylaxis - 0.5 - 0.8 mEq/L Toxic - >2 mEq/L