The compositions and methods of this invention are used to assess the level of immune competence of tested individuals based on the degree of immune response as a surrogate marker of CD4 T Cell lymphocytes as measured by the intensity of the resultant skin reaction score following controlled topical application of a unique anhydrous composition containing a contact sensitizer. The results of assessment are useful in determining appropriate treatment of immuno-compromised patients. Preferred compositions contain, but are not limited to, Diphenylcyclpropenone as a preferred embodiment of the class of contact sensitizing agents applied to the skin in an optimally prepared formulation preferably containing about 0.4% of the contact sensitizer.