Absolute Lymphocyte Count (ALC)

Why Use

Serves as a surrogate for CD4 count in HIV patients who are naive to antiretroviral therapy in resource-limited areas.

When to Use

Frequently used in the ED setting because CD4 tests take longer to come back and need patient consent. Used in limited-resource settings where CD4 tests are costly or unavailable.

Formula

Pearls / Pitfalls

If the ALC is low, the CD4 will usually be low ( Shapiro 1998 ). Currently evidence is mostly around HIV-1 treatment-naive patients. Other viral infections such as influenza or EBV can cause lymphopenia. Does not aid in the diagnosis of HIV.

Critical Actions

Does not change management, but helps support the suspicion of HIV infection with low CD4.

Advice

In the right clinical context, consider undiagnosed HIV as a cause of low lymphocyte count. If available, obtain a CBC with differential and CD4 count for confirmation.

More Information

Predicted CD4 from ALC ( van der Ryst E 1998 ) ALC Predicted CD4 Count <1000 cells/mm 3 <200 cells/mm 3 1000-2000 cells/mm 3 Unable to predict >2000 cells/mm 3 >200 cells/mm 3