The competency of the immune system can be assessed with several specialty tests. Secretory Immunoglobulin A (SIgA) can be measured from saliva and also from stool specimens. SIgA is the main antibody that protects the mucous membranes from foreign invaders. The mucous membranes are those tissues lining the respiratory, genitourinary, and the gastrointestinal tracts. Intestinal SIgA is particularly important. It binds, neutralizes, and helps the body excrete parasites, toxic bacteria and fungi, viruses, toxins and food antigens. SIgA is referred to as "the first line of defense." When levels of SIgA are elevated it means the immune system is engaged in battling a [perceived] foreign invader. Low levels of SIgA are a sign of weakened immunity and necessitate therapeutic intervention to restore levels to normal. 

Another example of an important test for immune function is Natural Killer Cell Activity. Natural killer cells are white blood cells that are focused on killing tumor cells and viruses. From a blood sample, the laboratory measures the speed with which the individual’s natural killer cells destroy tumor cells. When natural killer cell activity is found to be below normal, holistic natural therapies can be used to boost natural killer cell activity.