Performance of a fully automated quantitative neopterin measurement assay in a routine voluntary blood donation setting

Abstract

Acute virus infections are indicated by increased serum neopterin concentrations. Testing of blood donations for increased neopterin was introduced in the Austrian Tyrol in 1986 and throughout Austria in 1994 to improve the safety of blood transfusions. Radioimmunoassay (RIA) was the first available test, and the 98th percentile for neopterin concentrations from 76,500 donations was defined as the cut-off threshold, excluding donations with neopterin >or=10 nmol/L. When ELISAs were introduced on fully automated test systems to measure neopterin concentrations, results were generally higher and the cut-off was adjusted up to 12 nmol/L. In early 2006, new equipment (Hamilton Microlab Star pipettor + Dade Behring ELISA Processor III, BEP III) became available which monitors sample and reagent volumes for each uptake and dispense, and takes the viscosity of the fluids into account. Using this system, the performance of neopterin determinations was evaluated over 21 months and compared to earlier data. When the new apparatuses were introduced, an immediate decrease in mean neopterin concentrations and the percentage of samples with neopterin concentrations >or=10 nmol/L was observed. The 55,516 measurements performed in 2007 showed a mean value of 5.5 nmol/L. Neopterin in 680 donations (1.23%) were >or=10 nmol/L. The new Hamilton diluter increased the accuracy of the neopterin test procedure. Results are now identical with those of RIA and ELISA when run in a semi-automated manner. Differences in pipetting performance of standards and samples are considered as one possible explanation for the earlier discrepancies seen with the automated apparatus.