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      Calc Function

    • Calcs that help predict probability of a diseaseDiagnosis
    • Subcategory of 'Diagnosis' designed to be very sensitiveRule Out
    • Disease is diagnosed: prognosticate to guide treatmentPrognosis
    • Numerical inputs and outputsFormula
    • Med treatment and moreTreatment
    • Suggested protocolsAlgorithm





    Chief Complaint


    Organ System


    Patent Pending

    Absolute Lymphocyte Count (ALC)

    Assesses number of lymphocytes and predicts CD4 count.


    We launched a COVID-19 Resource Center, including a critical review of recommended calcs.

    Tips for COVID-19: Use after diagnosis to determine dispo. Lymphopenia appears to be a predictor of COVID infection.

    When to Use
    Why 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.

    • 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.

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

    × 10³ cells/µL
    Confirmed positive
    Confirmed negative


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    Next Steps
    Creator Insights


    • 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.

    Critical Actions

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

    Content Contributors
    • Alex Lazo, MD
    About the Creator
    Dr. Nathan Shapiro
    Are you Dr. Nathan Shapiro?
    Content Contributors
    • Alex Lazo, MD