Interleukin-6 and neopterin in renal transplant recipients: a longitudinal study

Serum and urine interleukin-6 (IL-6) levels and serum neopterin/creatinine ratios were longitudinally studied in 86 renal transplant recipients until 4 months after transplantation. During acute rejection and acute tubular necrosis (ATN), serum and urine IL-6 levels were elevated compared to during stable transplant function (P < 0.001). During acute rejection, serum IL-6 levels increased at least 2 days before plasma creatinine started to rise (P < 0.05), indicating its early involvement in the rejection process. During cytomegalovirus (CMV) disease, serum, but not urine, IL-6 levels were higher (P < 0.01), and serum neopterin/creatinine values were higher than during stable transplant function, ATN, or acute rejection (P < 0.01). No significant differences with stable transplant function occurred during cyclosporin A toxicity. Measurement of serum IL-6 provided a sensitivity of 84% and a specificity of 85% for the diagnosis of acute rejection episodes not coinciding with ATN. All cases of CMV disease could be diagnosed by measurement of serum neopterin/creatinine, which provided a specificity of 73%.