Measurement of theophylline in dried blood spots by spectrophotometric enzyme immunoassay.

A widely-used enzyme immunoassay for the measurement of theophylline in plasma (EMIT) has been adapted for use with dried blood spots. Potential interference from haemoglobin in eluates of the spots was avoided by autoclaving them prior to analysis. The method was investigated in terms of the recovery of theophylline added to samples, precision, and the correlation of results in DBS with those in plasma samples. The recoveries of some other drugs from eluates of autoclaved DBS were also investigated.