<prompt> Most sensitive and specific test for diagnosis of iron deficiency is -Serum iron levelsSerum ferritin levelsSerum transferrin receptor populationTransferrin saturation  <response>: Plasma ferritin is a measure of iron stores in tissues is the best test to confirm iron deficiency is a very specific test . Plasma iron total iron binding capacity are measures of iron availability ;hence they are affected by many factors besides iron stores.Plasma iron has a marked diurnal day to day variation becomes very low during an acute phase response. Levels of transferrin are lowered by malnutrition ,liver disease,acute phase response , nephrotic syndrome.A transferrin saturation of less than 16is consistent but is less specific than a ferritin measurement .Reference : Davidson;s principles practice of medicine 22nd edition pg no-1023 