absolute lymphocyte count vs. CD4 count (for PCP – pneumonia)

7 May

Some patients know their last CD4 count, some will have records/recent labs, many will not know or be unable to tell you.  CD4 counts are not typically a rapid attainable value in the ER setting.   So now what?  Is there another way?



5-year retrospective chart review; ED’s in Rhode Island, Washington, D.C.

included patients who had an absolute lymphocyte count (ALC) and CD4 count in <24 hrs

686 patients with pneumonia, 23.2% diagnosed with PCP



HIV patients, CD4 count is an indicator of how immunosuppressed your patient is

  • CD4 count <200 = increased risk for opportunistic infections (e.g. pneumocystis jiroveci pneumonia)
  • CD4 count <200 pts usually get prophylactic or empiric TMP/SMX (bactrim) treatment


DOES ALC correlate to CD4 count?

  • sort of.
  • correlation coefficient = 0.6


some numbers:

  • ALC <1700 cells/mm3 had
    • sensitivity 84% for CD4 <200 cells/mm3
    • specificity 55% for CD4 <200
    • positive likelihood ratio 1.85
    • sensitivity 86% for PCP
    • specificity 35% for PCP


  • ALC <2500
    • sensitivity 95% for CD4 <200 cells/mm3
    • specificity 22% for CD4 <200
    • positive likelihood ratio 1.21


  • ALC <800
    • sensitivity 39% for CD4 <200 cells/mm3
    • specificity 91% for CD4 <200
    • positive likelihood ratio 4.26



common sense utility: very low ALC, be more suspicious for low CD4; higher CD4 count, less likely to have a crappy CD4

BUT…ALC alone not ready for primetime use for identifying PCP pneumonia patients  (ALC <1700 had 2.5:1 ratio of  false positive: true positive identification in this study), as correlation (to CD4) is not the best


References: article; picture


One Response to “absolute lymphocyte count vs. CD4 count (for PCP – pneumonia)”


  1. WBC – too high or too low? | DAILYEM - October 23, 2015

    […] TANGENT, since we’re talking about low immune response… REFRESHER on CD4 estimation: (link it) 10 second version: absolute lymphocyte count = ALC  ALC < 2500 (95% sensitive for CD4 <200) […]

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: