Homogeneous enzyme immunoassay (EMIT) protocol for monitoring tricyclic antidepressants on the COBAS-BIO centrifugal analyzer.

EMIT tests are available for quantitative determination of the tricyclic antidepressants amitriptyline (AMI), nortriptyline (NORT), imipramine (IMI), and desipramine (DMI). An extraction step before analysis eliminates cross-reacting polar metabolites. Excellent correlation between EMIT and high-performance liquid chromatography (HPLC) has been previously established. Most published protocols for using EMIT reagents on COBAS-BIO centrifugal analyzers were designed for analytes present at 1-50 mg/L in serum. AMI, NORT, IMI, and DMI are usually present at far less than 1 mg/L. We describe a COBAS-BIO EMIT protocol for assaying these analytes. Patient sample correlation between COBAS-BIO EMIT and EMIT-AutoLab were greater than 0.99. Between-run precision for single-point determinations was comparable to SYVA AutoLab performance [less than or equal to 11% at 40 micrograms/L AMI, NORT, IMI (80 micrograms/L DMI), and less than or equal to 4% at 200 micrograms/L AMI, NORT, IMI (400 micrograms/L DMI)]. With stored-curve updating, working reagents were usable for at least 14 days (AMI) or 23 days (DMI).