Inter-laboratory comparison of chronic myeloid leukemia minimal residual disease monitoring: summary and recommendations

Abstract

In patients with chronic myeloid leukemia, the use of real-time quantitative reverse transcription-polymerase chain reaction (qRT-PCR) for measuring BCR-ABL1 transcripts has become standard methodology for the diagnosis and monitoring of minimal residual disease. In 2004 and 2005, 38 different laboratories from North America participated in three separate sample exchanges using real-time qRT-PCR to measure RNA transcript levels in unknown diluents of a BCR-ABL1-positive cell line, K562. In this study we compared results of quantitative testing for BCR-ABL1 from laboratories using different platforms, internal controls, reagents, and calculation methods. Our data showed that there can be considerable variability of results from laboratory to laboratory, with log reduction calculations varying from 1.6 to 3 log between laboratories at the same dilution. We found that none of the variables tested had a significant impact on the results reported, except for the use of ABL1 as the internal control (P < 0.001). Laboratories that used ABL1 consistently underreported their log reduction values. Regardless of the specific methodology and platform used for real-time qRT-PCR testing, it is important for laboratories to participate in proficiency testing to ensure consistent and acceptable test accuracy and sensitivity. Our study emphasizes the need for optimization of real-time qRT-PCR before offering clinical testing and the need for widely available universal standards that can be used for test calibration.

Table 5

Summary of Results for the AMP (Laboratories 1 to 29) and GLEEM (Laboratories 30 to 48) Sample Exchanges

Figure 1

Mean of the log reduction variation using different internal controls. The mean log reduction for all laboratories using the same internal control was calculated for each dilution. Six internal controls (ABL1, GAPDH, BCR, G6PD, GUSB, and B2M) were used from different laboratories for this analysis. Note that the log reduction calculated when using ABL1 as an internal control is consistently lower than the known dilution value.