The G2 chromosomal radiosensitivity assay.

Although requiring stringent experimental conditions to achieve good reproducibility, the G2 assay has potential as a sensitive marker for cancer susceptibility, and is particularly useful in population studies. Immediate culture of blood is preferable, but overnight storage of blood either at ambient temperature or at 4 degrees C does not appear significantly to affect G2 scores. Transport of blood may lead to additional variability in assay results and should be well controlled. Although reproducibility is generally good, G2 scores on blood from certain individuals appear to show significant variability in repeat samples. Thus, determination of an individual's radiosensitivity may require multiple assays on different occasions. While it is recognized that the distinction between aligned and mis-aligned discontinuities has no scientific basis, some laboratories have decided for the purpose of record-keeping to score all aligned discontinuities as gaps, and mis-aligned discontinuities as breaks. In all cases the final G2 score should comprise the sum of all gaps and breaks.