Example of the use of a conversion factor to convert BCR-ABL values obtained in a given laboratory to the international scale
Laboratory . | MMREq, % . | 0.1%MMREq (%) = conversion factor . | Formula for conversion of a given result to the international scale (BCR-ABLL × CF = BCR-ABLIS) . |
|---|---|---|---|
| Adelaide | 0.08 | 0.1/0.08 = 1.25 | BCR-ABLL × 1.25 |
| Mannheim | 0.12 | 0.1/0.12 = 0.83 | BCR-ABLL × 0.83 |
| London | 0.045 | 0.1/0.045 = 2.22 | BCR-ABLL × 2.22 |
Laboratory . | MMREq, % . | 0.1%MMREq (%) = conversion factor . | Formula for conversion of a given result to the international scale (BCR-ABLL × CF = BCR-ABLIS) . |
|---|---|---|---|
| Adelaide | 0.08 | 0.1/0.08 = 1.25 | BCR-ABLL × 1.25 |
| Mannheim | 0.12 | 0.1/0.12 = 0.83 | BCR-ABLL × 0.83 |
| London | 0.045 | 0.1/0.045 = 2.22 | BCR-ABLL × 2.22 |
BCR-ABLL = BCR-ABL/control ratio expressed as a percentage in a given laboratory. MMREq = BCR-ABLL that is equivalent to a MMR as extablished in the IRIS trial.12 In order to convert a given local result to the international scale, it is necessary to use a conversion factor (CF). This is calculated as follows: CF = 0.1% divided by MMREq (since 0.1% is the agreed value for MMR on the international scale). Once a laboratory-specific conversion factor has been derived, it can be used to convert all local values to the international scale. (This calculation will be invalid if the reproducibility or linearity of the assay is poor, in which case the methodology will need to be optimized.)