Blood samples will be collected from HIV infected adolescents and adult men and women presenting to a physician's office or outpatient clinic. Capillary whole blood samples will be obtained by fingerstick in duplicate from all Subjects in the study for immediate measurement of CD4+ T-cell count on the Pima CD4 Test by a trained healthcare professional. Venous whole blood samples from all Subjects in the study will also be collected and transported to the clinical laboratory of each study site for concurrent testing on the reference method by a trained laboratory professional. Venous samples from all Subjects in the study will also be measured on the Pima CD4 Test at the study site. Hematocrit will also be measured for all Subjects.