Background:  Established standards for determining degree of immunologic suppression are not based on data from African children. Among children in Botswana, we have frequently noted discordance between immunologic categorization determined based on CD4⁺ T lymphocyte absolute count and CD4⁺ T lymphocyte percent in all age groups. This preliminary study was designed to determine the extent to which treatment decisions would vary in our population depending on whether the treatment decisions were guided by CD4⁺ T lymphocyte % or absolute count.
Methods:  Prior to initiation of ART, 1052 patients between the ages of 2 months and 15 years received baseline CD4⁺ T lymphocyte testing. The degree of immune suppression was determined using World Health Organization (WHO) and Centers for Disease Control and Prevention (CDC) immunologic classification systems. Results were stratified by age to illustrate the extent to which the current age-related classification systems result in concordant CD4⁺ T lymphocyte percentage and absolute categorization in the different age bands.

Results:  A high rate of immune classification discordance was noted in all age bands using both classification systems. A total of 661 patients presented with severe immune suppression based on either the WHO percentile or absolute count definition. Of those, only 384 (58%) had severe immune suppression using both CD4⁺ T lymphocyte absolute counts and CD4⁺ T lymphocyte percentage. Younger children were more likely to be concordantly classified as severely immune suppressed using both CD4⁺ T lymphocyte percentage and absolute counts. Among children between 6 and 12 years of age, 115 had CD4⁺ T lymphocyte counts <200 cells/mm³ and CD4⁺ T lymphocyte percentage <15%. In this age bracket, 102 children had CD4⁺ T lymphocyte percentage of <15%, but absolute CD4⁺ T lymphocyte counts >200 cells/mm³. The consideration of both CD4⁺ T lymphocyte percentage and absolute count would have resulted in nearly twice as many patients being classified as severely immune suppressed compared with classification based on CD4⁺ T lymphocyte absolute count alone.

Conclusions:  The high rate of discordance between immunologic classifications based on CD4⁺ T lymphocyte absolute count or percentage in our population, particularly in children >6 years of age, suggests that treatment decisions based only on the CD4⁺ T lymphocyte absolute count, without regard for the CD4⁺ T lymphocyte percentage may result in under-treatment. These data underscore the need to validate immunologic classification systems for African children.