A 50-year-old man presents with 3-months history of jaundice, arlhralgia, Increase in skin pigmentation, and upper abdominal discomfort. He is on oral hypoglycemic medications for recently diagnosed diabetes mellitus. His viral hepatitis screening was negative. Examination revealed a bronze coloured skin, enlarged liver with span of 15 cm. no splenomegaly, and testicular atrophy. Cardiac examination revealed a 3rd heart sound (see lab results). Test Result Notmal Values
Direct bilirubin 24 1.5-6.5 pmol/L
Total bilirubin 31 3.5-16.5 pmol/L
Aspartate aminotransferase 79 12-40IU/L
Alanine aminotransferase 112 5-40IUZL
Alkaline phosphatase 109 39-117 IU/L
Random Glucose 7 3.9-5 5 mmol/L
Ferritin 400 20-300 pg/l (Male)
20-120 pg/L (Female)
Which of the following investigations is the most appropriate next step?