<prompt> A PATIENT WAS ON LITHIUM THERAPY FOR BIPOLAR DISORDER FOR 6MONTHS SHE KEPT THE FAST FOR FEW DAYS .SHE PRESENTED WITH S3 , COARSE TREMORS , CONFUSION AND WEAKNESS OF LIMBS. WHICH OF THE FOLLOWING SHOULD BE DONE NEXT TO ASSESS HER CONDITION ?S.ELECTROLYTESECGMRIS.LITHIUM LEVELS  <response>: REF : KD TRIPATHI 8TH ED 