Certain Medications they may be on can alter or mask issues.
The other thing to remember is the Asyra/Qest system allows the body to choose a starting point for the order of things to be addressed. So the body may need to take care of certain issues before addressing others. Example: someone has Lyme Disease and Lyme does not show on the comprehensive but viral conditions and spleen issues do. This does not mean it is not detecting lyme; it means the body must clear the viral and spleen issues before addressing the lyme.
Also, we have had practitioners say things like "I had a client with strep throat and ran a scan and it did not show up". We told them to send the scan to us, and upon review we saw an Antibody disturbance and Immune system was on the comprehensive. They had not put it together that the energetic pattern chosen for the strep was identified through Immune pattern and the Antibody pattern.