Lymphocyte Subset Enumeration (CD4% & Absolute count)

What is a normal CD4 count and percentage for a healthy person?

Normal CD4 count or biological reference range for CD4% is 27-51 % and absolute count is 448-1611 Cells/µL. It is advisable to consider both CD4 percentage and absolute counts in cases of discordant results. T-lymphocyte antigen, CD4 is a biomarker for normal T-helper cells and plays an important role in T-cell activation. It maintains peripheral tolerance and prevents autoimmunity. T-cells co-expressing both CD4 and CD8 are undergoing thymic maturation or migration and are present at very low levels in normal blood.

How do you know your CD4 count?

Venipuncture is done and Random non-fasting blood sample is collected. This test is done by Flowcytometry analysis. In this test, first the lymphocytes are separated from other white blood cells using CD45 gating. Then T lymphocytes expressing CD3 are separated out and subsequently absolute value and percentage of CD4 (Helper T) cells in a given sample is reported. Factors affecting CD4 counts include circadian rhythm (day and night cycle), time of collection, age, sex, seasonal variation, menstrual cycle, pregnancy, ethnicity, any ongoing stress, recent surgery, effect of drugs like chemotherapy, corticosteroids, immunosuppressive or anti-rejection medications, presence of anti lymphocyte antibody, splenectomy, smoking, infections, delay in analysis, sequential use of different assay and sample storage.

What are the indications of doing CD4 testing?

Indications for doing CD4 test are as follows:

A) HIV infection: Serial monitoring is done in HIV patients to determine the stage, severity and outcome of the infection. It tells us about patient’s immune system, disease progression, predict for future complications and effectiveness of antiretroviral treatment. It is essential to obtain baseline CD4 counts before starting HIV treatment.

B) Classification and diagnosis of T cell lymphoproliferative disorders (LPDs) like Sezary syndrome/cutaneous T-cell lymphoma, T-cell prolymphocytic leukemia, acute T-cell leukemia/lymphoma, anaplastic large cell lymphoma, angio-immunoblastic T-cell lymphoma and indolent small intestinal T-cell lymphoma. Rarely it may also be seen in T-cell large granular lymphocyte leukemia and acute myeloid leukemia (M4, M5).

C) T-cell immune monitoring in patients of organ transplantation, autoimmunity and other immune-related disorders who have received immunosuppressive and immunomodulatory therapies.

D) To assess T-cell immune reconstitution after hematopoietic stem cell transplantation.

E) Screening, diagnosis and follow up of congenital disorders like DiGeorge syndrome, other primary cellular immunodeficiencies and severe combined immunodeficiency disorder.

F) Seeing baseline counts in immunodeficient patients before starting antimicrobial therapy.

G) Early screening to look for quantitative T-cell anomalies in infection or malignancy patients.

What happens if your CD4 count is low?

CD4 helps in monitoring body’s T cell status. It gives us a broad overview of an individual’s immune system. CD4 cells are one of the important targets for HIV-Human immunodeficiency virus. As HIV infection progresses CD4 cell count decreases and susceptibility of getting various opportunistic infections and complications increases. CD4 values <400 Cells/µL increases the chances of getting opportunistic infections. In HIV patients before doing any treatment modifications owing to an unexpected result, always repeat CD4 testing. There is profound CD4 depletion in HIV infection and it is always advisable to calculate absolute values of CD4 and CD8. Depending upon the CD4 values, clinician will decide the treatment strategy to improve their status.

For disease monitoring, is single CD4 count sufficient?

No. CD4 counts in the blood may change up to 30% without any changes in clinical status due to biological and method variation. So it is advisable to do serial monitoring and observe trends over a period of time rather than change in a single specific test result. In case of HIV patients, CD4 counts every 3-6 monthly is advisable. It is always recommended to do follow up testing at the same time of the day to avoid the effects of diurnal variation.