Dissociation of neopterin and 7,8-dihydroneopterin from plasma components before HPLC analysis

Measurement of plasma neopterin by HPLC with fluorescence detection is used clinically as a marker of immune cell activation in the management of a number of disease pathologies. HPLC analysis of neopterin requires the acidic removal of plasma proteins but we have found that 7,8-dihydroneopterin is oxidised to neopterin with varying yield. Using acetonitrile as the precipitant, we have measured substantially higher quantities of both total neopterin (7,8-dihydroneopterin and neopterin) and neopterin from plasma of healthy and septicemia patient's. Total neopterin concentrations were on average 50% and 200% greater in healthy and septicemia subjects, respectively, when measured after acetonitrile precipitation compared to trichloroacetic acid. Our data suggests that some pterin co-precipitates with proteins during acid treatment.