TABLE I.

Classification Criteria for Determination of EBV Infection as the Primary Process Causing HLH

Parameter	Points
EBV load (PCR) <5,000 copies/ml	1
EBV load (PCR) >5,000 copies/ml	2
Duration of EBV viremia <1 month	1
Duration of EBV viremia >1 month	2
Presence of EBV in tissues	2
Evidence (history, serologies, PCR) of exposure to other virus associated with HLH	−1
Alternative etiologies for HLH	−1

EBV, Epstein–Barr virus; HLH, hemophagocytic lymphohistiocytosis; PCR, polymerase chain reaction.

⁽¹⁾Determination of EBV infection as the primary process causing HLH: definite: 6 points; probable: 3–5 points; possible: 1–2 points.

⁽²⁾Low levels of EBV viremia were defined as EBV titers <5,000 copies/ml based on the reviewed literature of previous EBV-HLH cases.

⁽³⁾High levels of EBV viremia were defined as EBV titers >5,000 copies/ml based on the reviewed literature of previous EBV-HLH cases.

⁽⁴⁾Short duration of documented EBV viremia was defined as <1 month based on the reviewed literature of previous EBV-HLH cases.

⁽⁵⁾Prolonged duration of documented EBV viremia was defined as >1 month based on the reviewed literature of previous EBV-HLH cases.

⁽⁶⁾Alternative etiologies for HLH may include presence of other factors well known to be associated with HLH, such as other viral, fungal infection, immunodeficiency.