One year old baby exclusively breast fed has a 1cm. hepatomegaly severe pallor and no spleen.The most important investigation is –

By the age of 6 months the breast-fed infant's diet should be supplemented with iron fortified complementary foods because iron in breast milk is sufficient upto the age of 6 months. The baby in question has been exclusively breast fed upto 1 year, so he has developed iron deficiency anemia.