Well, I'm not sure if you're referring to an specific protocol, but in my opinion one of the best ways to quantify DNA lesions (and indirectly its repair) is this method described in this article:

http://www.ncbi.nlm.nih.gov/pubmed/16673882

The only thing you might have to pay attention is how you will extract your DNA. This method uses QIAGEN Genomic Tip Kit, which implies a gravity column in order to preserve the DNA better, and it recommends to use the "tissue protocol", even if you're using cells. In the case of blood samples, I'm not sure if it's also recommended to use the "tissue protocol" or the "blood protocol".

Hope it helps you

Good luck

http://www.sigmaaldrich.com/life-science/cell-biology/cancer-research/learning-center/cancer-research-protocols/comet-assay.html

http://www.cometassayindia.org/Protocol%20for%20Comet%20Assay.PDF