A deletion in the end region of the long arm of a Chromosome 9 is efficiently detected.A genetic testing kit of bladder cancer according to the present invention includes a primer allowing for efficient amplification of a region containing a site of genetic polymorphism present in the ABO blood group gene of Chromosome 9. In the site of genetic polymorphism present in the ABO blood group gene, the frequency of heterozygote (heterozygosity) in the population is extremely high. Therefore, by detecting LOH using a polymorphic site present in the ABO blood group gene, it is possible to reliably detect a deletion near the polymorphic site, in other words, a deletion near the end of the long arm of Chromosome 9.