FIGURE 1. The Bethesda criteria are used as a guide to screen patients for genetic testing, which is offered in the context of genetic counseling. For those who meet these criteria and decide to pursue testing, A636P and MSI (with or without IHC) are ordered simultaneously, when possible. Since tissue for MSI (microsatellite instability) and IHC are often difficult to obtain and prepare for analysis, A636P results are typically ready before the results of these tests are available. In the case of an A636P-positive result, MSI and IHC analyses are not considered necessary. Since an A636P-negative result does not exclude the possibility of other MMR mutations, in these cases MSI and IHC analysis should be undertaken. If these are abnormal, sequencing and Southern blot should then be performed.