Development of a specific polarisation fluoroimmunoassay for paracetamol in serum

A specific polarisation fluoroimmunoassay for the measurement of paracetamol levels in serum has been developed for use in emergency toxicological screening. It is based on the use of a fluorescein-labelled analogue and a sheep antiserum and exploits the rapid dissociation kinetics of the hapten-antibody complex to enable the label and antiserum to be combined as a single reagent. Paracetamol levels are determined by adding 5 microL of serum to 1.5 mL of the single reagent, incubation at ambient temperature for a few minutes and measurement of fluorescence polarisation. In addition to its speed and simplicity, the assay is both accurate and precise and the results obtained correlate closely with those from the commonly used chemical and enzymatic techniques.