• Youssef Annous, Sara Manning, and Danya Khoujah.
• Department of Emergency Medicine, University of Maryland School of Medicine, Baltimore, MD 21201, USA. Electronic address: yannous@som.umaryland.edu.
• Am J Emerg Med. 2021 Oct 1; 48: 249-254.

AbstractFever of unknown origin (FUO) is defined as persistent fevers without an identifiable cause despite extensive medical workup. Emergency physicians caring for patients reporting a persistent, nonspecific, febrile illness should carefully consider potentially serious non-infectious causes of FUO. We present a case of a 35-year-old man who presented to the emergency department (ED) three times over a 10-day period for persistent febrile illness and was ultimately diagnosed with Adult-Onset Still's Disease (AOSD) after a serum ferritin level was found to be over 42,000 μg/L. AOSD, along with macrophage activation syndrome, catastrophic antiphospholipid syndrome, and septic shock comprise the four hyperferritinemic syndromes. These are potentially life-threatening febrile illnesses that characteristically present with elevated ferritin levels. In this article, we highlight the value of a serum ferritin level in the workup of a patient with prolonged febrile illness and its utility in facilitating early diagnosis and prompt treatment of hyperferritinemic syndromes in the ED.Copyright © 2021 Elsevier Inc. All rights reserved.

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