An idiopathic epileptic patient is on phenytoin and tricyclic antidepressent.He becomes easily fatigue and lethargy.His Hb 8.2 gm%,TLC 9600 cmm.Serum bilirubin 0.6,SGPT 25 IU/lit.The next investigation done is:

• A. MCV
• B. Gamma glutamy transferase assay
• C. Chest X-ray
• D. Urine culture