Soluble H4 (sH4) levels have been discovered to correlate with the stage or severity of inflammatory disorders including autoimmune disorders. In particular, circulating levels of sH4 can be used as a diagnostic for determining the severity of an inflammatory disorder or the propensity for developing an inflammatory disorder. The severity of an inflammatory disorder can be determined by assaying the levels of sH4 in a subject and comparing the levels of sH4 to reference sH4 concentrations that correlate to specific stages of an inflammatory disorder. The therapeutic efficacy of treatments for inflammatory disorders can also be determined by comparing levels of sH4 before and during treatment. Methods and devices for measuring sH4 are also provided.
