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3. Ferritin
The antinuclear antibody (ANA) is a nonspecific reactant seen in a variety of diseases. Similarly, the erythrocyte sedimentation rate (ESR) is a non-specific acute phase reactant only occasionally valuable in making a specific diagnosis – for instance, it can be useful in patients with a high clinical pretest probability for the diagnosis of temporal arteritis. Procalcitonin is released by a wide variety of human cells in response to systemic bacterial infection. Although initially promising as a tool to identify bacterial sepsis, it lacks sensitivity and specificity and should generally not be used to make decisions about whether empirical antibiotics should be started. There is some evidence that it might be helpful in discontinuing antibiotics in patients with community acquired pneumonia, but the value of that practice has recently been called into question. Rheumatoid factors are antibodies against the Fc portion of IgG. They are non-sensitive and non-specific for rheumatoid arthritis and likely are used mostly because of historical overestimation of their clinical value. Our patient’s presentation was not compatible with RA and she did not have arthritis on physical examination. RF is typically negative in the majority of patients with Stills.
Ferritin is also a non-specific acute phase reactant, but it is typically strikingly elevated in cases of Still’s disease or HLH. These diagnoses are much less likely if ferritin is <500 ng/mL, and clinical suspicion is increased if ferritin is very elevated (i.e. >2000 ng/mL). Other easily-obtained laboratory findings of HLH include hypofibrinogenemia and hypertriglyceridemia.
Further lab testing of our patient revealed:
The patient is presenting with presumed sepsis unresponsive to broad spectrum antibiotic therapy, with persistent fever, progressive multisystem organ failure, bicytopenia and severe hyperferritinemia. This syndrome is most compatible with the diagnosis of secondary HLH.
What should be done next? (Click on the correct answer to be directed to the fourth of six pages)