Plasma neopterin as an adjunct to C-reactive protein in assessment of infection.

C-reactive protein (CRP) concentrations are increased in plasma in people with inflammatory conditions and bacterial infections. Plasma neopterin concentrations are increased in people with bacterial septicemias, viral infections, and graft vs host disease. Plasma concentrations of CRP and neopterin were measured daily in 21 bone-marrow transplant (BMT) patients, 64 patients in intensive-care units (ICU), and 12 patients with squamous cell carcinoma of the head and neck (HN). In the BMT patients, plasma neopterin measurements in addition to CRP measurements allowed infectious episodes to be distinguished from graft vs host disease. In the ICU patients, increased concentrations of CRP were not specific for infection and the additional plasma neopterin measurements did not improve this specificity. In all three patient groups, the derivation of a neopterin/CRP ratio was of no clinical use. These three groups of patients showed patterns of CRP and neopterin concentrations characteristic of their underlying diseases, the BMT patients with the immunological activation of graft vs host disease showed predominantly increased concentrations of plasma neopterin, ICU patients with infectious and inflammatory conditions had increased concentrations of both CRP and neopterin in plasma, and the HN group with localized inflammation showed increased plasma concentrations of CRP without increases in neopterin.