A child presents with complaints of oliguria, abdominal distension and diarrhoea. On examination there is deep jaundice. Hepatomegaly was present measuring 4 cm below the costal margin. Conjugated bilirubin in blood was 38 mg/dL, and there was urine urobilinogen and bile pigments. Hemoglobin was 4mg/dL and serum creatinine was 3mg/dL. Which of the following tests is of least impoance to diagnose this case -