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"However, these high [ferritin] values may be seen in other
conditions, such as after multiple blood transfusions and in severe liver
disease (haemachromatosis, Gaucher's syndrome), severe sepsis, HIV
infection, malignancies such as leukaemia and lymphomas, and
haemophagocytic syndrome. Hence ferritin concentrations have a limited use
in clinical practice."
Since almost all of the above conditions could be easily and quickly
excluded in the case case described, ferritin would indeed be
diagnostically useful. In practice I find a marked elevation in ferritin
to be a very effective way to increase or decrease the probability that a
patient has Still's disease, and an important trigger to add it to the
differential diagnosis in a patient with FUO, since the diagnosis can be
easily overlooked as there is no single diagnostic test for Still's