Luminescent oxygen channeling assay (LOCI): sensitive, broadly applicable homogeneous immunoassay method.

Luminescent oxygen channeling assay (LOCI) is a homogeneous immunoassay method capable of rapid, quantitative determination of a wide range of analytes--including high and very low concentrations of large and small molecules, free (unbound) drugs, DNA, and specific IgM. Assays have been carried out in serum and in lysed blood. Reliable detection of 1.25 microU/L thyrotropin (TSH) and 5 ng/L hepatitis B surface antigen (HBsAg) corresponds to detection limits approximately 3- and approximately 20-fold lower, respectively, than those of the best commercially available assays. An assay of chorionic gonadotropin is capable of quantification over a 10(6)-fold range of concentrations without a biphasic response. Latex particle pairs are formed in the assay through specific binding interactions by sequentially combining the sample and two reagents. One particle contains a photosensitizer, the other a chemiluminescer. Irradiation causes photosensitized formation of singlet oxygen, which migrates to a bound particle and activates the chemiluminescer, thereby initiating a delayed luminescence emission. Assay times range from 1 to 25 min.

Evaluation of EMIT Cyclosporine Assay for use with whole blood.

We evaluated the EMIT Cyclosporine Assay, designed for specific quantification of cyclosporine (CsA) in whole blood. The assay was run on the Roche Cobas Mira or Cobas Mira S analyzer. Analytical recovery from both normal donor whole blood and transplant patients' samples was within 17% of the standards. Measurement of diluted out-of-range samples also yielded excellent recovery (101-105%). Within-run, between-run, and total CVs were < or = 8.1%, 10.9%, and 12.1%, respectively. The detection limit was < 32 micrograms/L. The assay was linear from 0 to 500 micrograms/L. No significant cross-reactivity was observed for CsA metabolites AM1, AM19, and AM4N. Slight cross-reactivity occurred with metabolite AM9; 670 micrograms/L AM9 increased the measured CsA concentration by 49 micrograms/L. High concentrations of bilirubin, uric acid, triglycerides, and cholesterol, as well as 54 commonly coadministered drugs did not interfere with CsA quantification. Similarly, neither extreme values of hematocrit nor choice of anticoagulant affected CsA recovery. Sample extract stability was > 4 h, and assay calibration was stable for at least 2 weeks. Patients' samples analyzed by the EMIT assay showed strong correlation with both HPLC and 125I-RIA (r > 0.97). We conclude that the EMIT Cyclosporine Assay provides a convenient, accurate, and precise method for specific quantification of CsA in whole blood.