To the Editor.
—In his Editorial,1 Dr Volberding notes the stronger correlation between clinical stage and CD4+ percentage than with the absolute CD4+ cell count. He recommends that practitioners switch to use of this more stable marker of progression. To the array of arguments2 previously advanced for this change should be added simplicity and thrift.Many clinicians may not be aware of the redundant procedural burden introduced with the process of derivation of absolute CD4+ cell count from CD4+ percentage. Flow cytometry initially determines CD4+ percentage on a blood specimen. A separate white blood cell count and a differential are required to calculate the total CD4+ cell count. High coefficients of variation may be introduced by this additional step,3 which also increases laboratory costs. As CD4+ evaluation is now suggested every 3 months for patients infected with the human immunodeficiency virus, the US health care system could
Olson PE, Wallace MR. Measurement of CD4+ Percentage. JAMA. 1994;272(6):434. doi:10.1001/jama.1994.03520060032020