Answer:USMLE step 2 Mcq 184:A 64 year old man was admitted to the hospital for further investigation of diabetes and weight loss

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Correct Answer: B

Explanation:
Transferrin saturation (serum iron / total iron binding capacity) is the most sensitive blood test for hemochromatosis. A fasting sample is ideal. Unlike serum ferritin, it is abnormal at a young age in homozygotes and for this reason, it has been proposed as the preferred test in large scale screening studies such as in blood donors.1 Serum iron is an unreliable screening test with marked diurnal variation. Serum transferrin is a component of the total iron binding capacity and falls late in the disease. Serum ferritin is a marker of body iron stores and increases with age. It can also be elevated in the setting of inflammation and neoplasia. Both the serum ferritin and transferrin saturation should be interpreted with consideration of the patient's age, sex and other conditions predisposing to abnormalities in these tests. The mean serum ferritin and transferrin saturation in homozygote proband males at this centre is 2911µg/L and 85%, and in females is 1499 µg/L and 72%, respectively. The yield of investigating an isolated serum ferritin less than 1000 µg/L in an asymptomatic person with a normal transferrin saturation and no family history of hemochromatosis is low. An annual serum ferritin can be done in this setting and a rising ferritin would be a stronger indication to proceed to liver biopsy if no other source of chronic inflammation is apparent.


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