Modification of the Abbott Cyclosporine Monoclonal Whole Blood Assay

Laboratorio Central, Hospital General de Galicia, 15705 Santiago de Compostela, Spain
^a Author for correspondence. Fax 34-81-570-102

To the Editor:

Abbott Laboratories recommends that before every Cyclosporine Monoclonal Whole Blood Assay run on the TDx analyzer, a probe cleaning procedure be performed (1) to avoid an artifactual decrease of results in the first carousel position (2).

We asked whether non-use of this procedure significantly affected results for the sample in the first carousel position. In our study, the TDx analyzer underwent daily, weekly, and monthly maintenance, as recommended by the manufacturer. Between 15 and 20 samples were analyzed in each run, and the study was completed in a period of 2 months.

Fig. 1 shows the correlation and regression (Passing and Bablok method) found between the results obtained in the same run, in the first and any of the other carousel positions of the analyzer, for the cyclosporine A concentration in 70 whole-blood samples from liver and renal transplant patients. The difference between the means, although statistically significant (P <0.001), is not clinically significant according to the criterion of Harris (3) and the therapeutic interval in our laboratory.

View larger version (22K): [in this window] [in a new window]   Figure 1. Comparison of the values obtained in the first and any other carousel positions of the Abbott TDx analyzer, in the same analytical run, for the cyclosporine A (CyA) concentration in whole blood.

A CV of 2.5% was obtained using the method of replicates for the 70 pairs of values (interval, 120–929 µg/L; Fig. 1 ). This imprecision is similar to that found for 53 pairs of values, with a mean value of 445.1 µg/L (interval, 124–841 µg/L), obtained in the same run in other carousel positions, excluding the first position, for which a CV of 3.0% was obtained. In both cases, the CVs are similar to those reported by the manufacturer (1).

Given that the standard error of the estimate (S_yx = 12.62) is less than the clinically acceptable error according to the criterion of Harris (3), a probe wash procedure appears unnecessary before each assay run. Each laboratory, however, should determine the impact on state, county, or other laboratory certification of changes to commercial procedures.

Footnotes

Editor's note: A representative of the manufacturer warns about effects on laboratory certification of procedures that are contrary to the procedure provided by the manufacturer.

References

1. . Abbott Laboratories. TDx^® immunosuppressant drug assay 1995 Abbott Laboratories Cyclosporine monoclonal whole blood, no. 9797-60. Package insert. Chicago. .
2. Abbott Laboratories. TDx^® cyclosporine monoclonal whole blood reagents and accessories, lot no. 9797-69 [Technical Bulletin]. Chicago: Abbott Laboratories, 1996..
3. Harris EK. Proposed goals for analytical precision and accuracy in single-point diagnostic testing. Theoretical basis and comparison with data from College of American Pathologists proficiency surveys. Arch Pathol Lab Med 1988;112:416-420. [Web of Science][Medline] [Order article via Infotrieve]