In ED, we often encounter patients with known HIV infection but unknown CD4 count.  Any quick way to estimate the CD4 count so we can use it to guide treatment?

Thanks to Dr. Jacob Isserman, who recommended a retrospective cohort study published in PubMed in 2011, which concluded that there is an association between ALC (absolute lymphocyte count) and CD4 count.  Depending on pretest probability, this relationship could help us predict the likelihood of susceptibility to opportunity infections.

  •  If ALC is < 950 x 106cells/µL, CD4 is likely to be less than 200 x 106cells/µL.
  • If ALC is > 1,700 x 106cells/µL, then CD4 is less likely to be under 200 x 106cells/µL.

http://www.ncbi.nlm.nih.gov/pubmed/21496141

Study details:  A total of 866 patients (mean age 42 years, 40% female) met inclusion criteria.

An ALC of <950 × 10(6) cells/μL has a sensitivity of 76% (95% CI = 73% to 79%), specificity of 93% (95% CI = 87% to 96%), and positive likelihood ratio of 10.1 (95% CI = 8.2 to 14) for a CD4 count of <200 × 10(6) cells/μL.

An ALC of <1700 × 10(6) cells/μL had a sensitivity of 95% (95% CI = 93% to 96%), specificity of 52% (95% CI = 43% to 62%), and negative likelihood ratio of 0.09 (95% CI = 0.05 to 0.2) for a CD4 count of <200 × 10(6) cells/μL.

 

Another study with similar results published in 1998, with 807 patients.

http://www.ncbi.nlm.nih.gov/pubmed/9737494