Absolute Lymphocyte Count (ALC) Calculator

Variables and formula

The ALC calculator can be used to estimate the CD4 count (without having to go through complex and time consuming determining procedures) based on the white blood cell and lymphocytes count.

The absolute lymphocyte count formula is:

ALC = WBC count x % Lymphocyte in WBC x 1000

White blood cell differential count is one of the blood tests used in the diagnosis of conditions that affect the immune system:

■ Inflammatory illnesses;

■ Infections;

■ Tumors (leukaemia, lymphoma);

■ Immune deficiency.

The following table summarises the five types of WBCs and their involvement in the immune function:

CD4 count explained

Estimating CD4 count from ALC is often used instead of actual testing because of the elaborate method required, which takes a long time.

CD4 T lymphocytes are a laboratory immune indicator in patients with human immunodeficiency virus and can monitor efficiency of anti-retroviral therapy and progression of the virus towards acquired immunodeficiency syndrome (AIDS).

The following table introduces the correlation between ALC and CD4 levels.

Normal CD4 count is between 500 to 1,200 cells/mm³ and an ALC of less than 200 cells/mm³ is indicative of HIV progression to AIDS.

About the study

The study conducted by Shapiro et al. in 1998 was set to determine whether the absolute lymphocyte count (defined as white blood count multiplied by lymphocyte percentage) can be used to predict a low CD4 count.

807 samples from inpatient, clinic, and emergency department settings were retrospectively analysed by calculating:

■ Sensitivities;

■ Specificities;

■ Predictive values;

■ Likelihood ratios.

322 results (40%) had a CD4 count less than 200 cells/mm³ and it was found that ALC values lower than 1,000 cells/mm³ predicted CD4 counts less than 200 cells/mm³ with:

■ A sensitivity of 0.67;

■ A specificity of 0.96;

■ Positive predictive value of 0.91;

■ Negative predictive value of 0.81.

The study found that a reliable relationship exists between ALC and CD4 count and this can be used to identify patients with increased risk of opportunistic infection.

Original source

Shapiro NI, Karras DJ, Leech SH, Heilpern KL. Absolute lymphocyte count as a predictor of CD4 count. Ann Emerg Med. 1998; 32(3 Pt 1):323-8.

Other references

1. van der Ryst E, Kotze M, Joubert G, Steyn M, Pieters H, van der Westhuizen M, van Staden M, Venter C. Correlation among total lymphocyte count, absolute CD4+ count, and CD4+ percentage in a group of HIV-1-infected South African patients. J Acquir Immune Defic Syndr Hum Retrovirol. 1998; 19(3):238-44.

2. Kakar A, Beri R, Gogia A, Byotra SP, Prakash V, Kumar S, Bhargava M. Absolute lymphocyte count: a cost-effective method of monitoring HIV-infected individuals. Indian J Pathol Microbiol. 2011; 54(1):107-11.