Measurement of plasma caffeine concentrations by substrate labelled fluoroimmunoassay

Abuse or misuse of caffeine has been implicated in the pathogenesis of a variety of clinical disorders and measurement of its plasma concentration is likely to become important in clinical laboratories in the future. A rapid, sensitive and easily performed method for the measurement of caffeine in biological fluids by the technique of fluoroimmunoassay is described. The results produced are precise and agree well with those obtained by radioimmunoassay or HPLC. Cross-reactivity of the antiserum with other substituted xanthines and uric acids is negligible for the major metabolites of caffeine but there is significant cross-reactivity with theophylline at concentrations likely to be found when this drug is being administered therapeutically. The measurement of caffeine by fluoroimmunoassay has a place in the clinical laboratory particularly where small batches of samples are to be analysed.