If a patient’s CD4 count is unknown, the Absolute Lymphocyte Count (ALC) can act as a temporary surrogate.
ALC= WBC x % of Lymphocytes.
Here’s a quick review of the literature:
One of the more highly quoted studies states a CD4 count of <200 × 10(6) cells/μL is very likely if the ED ALC is <950 × 10(6) cells/μL and less likely if the ALC is >1,700 × 10(6) cells/μL, Napoli et al (2011).
Two studies performed in non-ED setting showed a good correlation between the CD4 count and ALC. There is some question as to whether these results are applicable or generalizable to the ED population, since all of the participants were tested during routine examinations, not while they were acutely ill, Blatt et al (1993) and Fournier AM et al (1993).
Another study, from Temple University, looked at 800+ samples of CBC + CD4 on HIV+ pt’s (ED & non-ED), Shapiro NI et al (1998).
While a single ALC threshold was neither sensitive nor specific for a low CD4 count, the investigators determined two valuable cut-offs of 1000 and 2000 cells/mm3.
– An ALC less than 1000 cells/mm3 was 91% predictive in identifying patients with CD4 counts less than 200 cells/mm3 (sensitivity only 67%, but specificity 96%).
– An ALC greater than 2000 cells/mm3 was 95% predictive in identifying CD4 counts greater than 200 cells/mm3.
The authors concluded that patients with ALCs greater than 2000 cells/mm3 might be less susceptible to opportunistic infections, while those with ALCs less than 1000 cells/mm3 are at higher risk. These researchers had no access to clinical data and couldn’t account for factors such as antiretroviral therapy or the presence of acute infection such as sepsis, pneumonia, or TB.
There are of course other studies which show the ALC isn’t great
Pirzada et al (2006), and others where it is decent.