Diagnostic testing for hemophagocytic lymphohistiocytosis.

Hemophagocytic lymphohistiocytosis (HLH) is a rare clinical syndrome caused by severe systemic hyperinflammation. HLH can be rapidly fatal if unrecognized or inadequately treated. It is important that clinicians are able to utilize diagnostic testing to assess for HLH and determine the underlying causes including possible inborn errors of immunity (IEI). This article summarizes many of the tools available to aid with the diagnostic evaluation of patients with possible HLH and underlying IEI.