When should I avoid taking the test or wait before collecting my sample?

In some circumstances, the DNA in the sample may not be reliable:  

• Bone marrow or haematopoietic stem cell transplant. We do not recommend taking the test. Saliva contains cells from your mouth, with your DNA, and white blood cells, which contain the donor's DNA after a transplant. This mixture often causes errors and, even if the analysis were successful, we would not know for certain whose results they were.  

• Low white blood cell count due to an illness or chemotherapy. White blood cells provide a substantial proportion of the DNA in saliva, so it is advisable to wait until their levels return to normal.