title: Relationship between CD4 count and CD4% in HIV-infected people.
abstract: OBJECTIVE
  To describe the relationship between absolute CD4 count and CD4%, and the influence on this of gender, risk group, age, a diagnosis of AIDS, use of zidovudine (ZDV) therapy and PCP prophylaxis.
  
  
  METHODS
  9203 paired serial measurements of CD4 count and CD4% on 1017 initially AIDS-free and ZDV-naive HIV positive patients from a London-based cohort were available for analysis. Multi-level regression procedures were used on log-transformed data to relate values of CD4 count to a given level of CD4%. We estimated the effect of selected covariates on this relationship from the exponent of the covariate coefficient.
  
  
  RESULTS
  A strong linear relationship was found between log CD4 and log CD4%, CD4 = e 1.78(CD4%)1.26 or 5.93 (CD4%)1.26 (excluding covariates). Based on this model, a CD4% of 5%, 15%, and 30% corresponded to an estimated CD4 count (95% confidence interval [CI]) of 45 cells/mm3 (17-117 cells/mm3), 182 cells/mm3 (64-499 cells/mm3) and 438 cells/mm3 (132-1395 cells/mm3), respectively. However, after adjustment for selected covariates, the predicted CD4 count for a given CD4% was found to be lower among heterosexuals and injecting drug users as compared with homosexual men by 30% and 17% respectively; following an AIDS diagnosis by 21%; and after initiation of ZDV therapy and PCP prophylaxis by 19% and 10%, respectively.
  
  
  CONCLUSIONS
  This analysis should be useful to clinicians and researchers in relating values of CD4 count to CD4%, although we have demonstrated that this is not a simple relationship. The wide CI observed in the estimated CD4 count particularly at high CD4% values, and the adjustments necessary according to risk group, following an AIDS diagnosis and use of ZDV and PCP therapy limit its application in the clinical setting.
authors.affiliation: HIV Epidemiology Unit, Chelsea and Westminster Hospital, London, UK.
authors.forename: L M
authors.initials: LM
authors.lastname: Yu
authors.forename: P J
authors.initials: PJ
authors.lastname: Easterbrook
authors.forename: T
authors.initials: T
authors.lastname: Marshall
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D019380:Anti-HIV Agents / Q000627:therapeutic use; D018791:CD4 Lymphocyte Count; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology*; D005260:Female; D015658:HIV Infections / Q000188:drug therapy / Q000453:epidemiology / Q000276:immunology*; D006801:Humans; D018655:Lymphocyte Count; D008297:Male; D008875:Middle Aged; D012307:Risk Factors; D012737:Sex Factors; D006113:United Kingdom / Q000453:epidemiology; D015215:Zidovudine / Q000627:therapeutic use
chemical_list: D019380:Anti-HIV Agents; D015215:Zidovudine