The enumeration of T lymphocytes positive for the CD4 antigen is used to determine the immune status of patients with, or suspected of developing, immune deficiencies such as AIDS. The BD FACS Presto™ is an investigational automated system for in vitro diagnostic use in performing the direct enumeration of CD4 absolute count, CD4 percentage of lymphocytes, and hemoglobin (Hb) concentration in human whole blood.

This is a prospective study to determine the relative bias between the investigational BD FACS Presto system and the predicate BD FACS Calibur with BD Tritest system in their determination of absolute CD4, % CD4, and Hb concentrations.

Inclusion Criteria:

• Subject has been infected with HIV and willing to provide informed consent to draw venous and capillary blood
• Specimen: Venous blood must be collected in blood collection tube with EDTA anticoagulant and stored at room temperature (20-25 °C) according to tube manufacturer's instructions
• Specimen: post enrolment staining within 24 hours
• venous blood of acceptable quality for flow cytometry, e.g. no hemolysis or clots and acceptable pre analytical handling)
• venous blood sample > 1 mL for sample preparation
• capillary blood applied to the investigational CD4/%CD4/Hb cartridge

Exclusion Criteria:

• Subject unwilling to disclose medical information regarding previous CD4 test results
• Subject unwilling to discuss medical information regarding co-morbid conditions and current medications

The study will enroll specimens from children 0-12 years and adolescent or adult patients 13 years of age or greater. Enrolment of children in the study is expected to satisfy the binning (stratification) requirements since relative lymphocytosis and higher CD4+ lymphocyte counts are normal in children less than 5 years of age.