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CD8+ T Cells, percent

The share of your lymphocytes that are CD8+ T cells. It is read together with the CD8 count and the CD4 results.

AI-verified against cited sources. Awaiting expert reviewAlso called CD8 pctLOINC 32518-3

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What it is

CD8+ T cells, often called cytotoxic or killer T cells, are lymphocytes (a type of white blood cell) that destroy cells infected by viruses or that have become abnormal. This result is the percent of all your lymphocytes that are CD8+ T cells. It comes from the same flow cytometry test as the CD4 and other T-cell results.

Why it matters

The CD8 percent shows the mix of your lymphocytes, not how many cells you have. If another group, such as CD4 cells, goes down, the CD8 percent goes up even if the number of CD8 cells has not changed. Clinicians usually read it alongside the absolute CD8 count and the CD4 results.

If it’s low

A low percent means CD8 cells make up less of your lymphocytes than usual. This can happen when other lymphocytes, such as CD4 or B cells, are a bigger share, or when CD8 cells themselves are low.

Common causes

  • Natural variation between draws and between labs
  • A higher share of other lymphocytes, such as B cells or CD4 cells
  • A recent acute illness
  • Medicines that suppress the immune system, including corticosteroids and chemotherapy
  • Advanced HIV infection, when CD8 cells can also fall
  • Rare inherited immune conditions

What can help

  • Ask your clinician whether the absolute CD8 count tells the same story
  • Share every medicine and supplement you take, including steroids

If it’s high

A percent above the lab's range means CD8 cells make up more of your lymphocytes than usual. This often happens during or after a viral infection, or when CD4 cells are lower. Many people with a high percent have no clear cause.

Common causes

  • Natural variation between draws and between labs
  • Recent or ongoing viral infection, such as infectious mononucleosis (Epstein-Barr virus) or cytomegalovirus (CMV)
  • A lower share of CD4 cells, as in HIV infection
  • Autoimmune or long-term inflammatory conditions
  • Smoking
  • Rarely, a blood disorder involving T cells

What can help

  • Ask your clinician to read it with the absolute CD8 count and the CD4 results
  • Ask whether repeating the test after any illness has passed makes sense

Usual ranges

What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.

The usual range depends on age. Choose an age to see the one that applies.

Children and teens 4 ranges

See CD8 % by age and sex, with the U.S. survey numbers where they exist.

What can affect your result

  • Age: ranges differ in infants and young children
  • Viral infections, including CMV and Epstein-Barr virus
  • The other lymphocyte groups: because this is a share of all lymphocytes, a change in CD4, B or NK cells moves it too
  • Medicines, especially corticosteroids and other immune-suppressing drugs
  • Lab and method: each lab sets its own range
  • Samples must reach the lab fresh. ARUP accepts EDTA blood for up to 72 hours at room temperature (48 hours for heparin) and rejects refrigerated or frozen samples.
  • Some medicines can change the result. ARUP asks that medicines be listed on the request form. Corticosteroids, chemotherapy and other immune-suppressing drugs are known to lower lymphocyte counts.
  • Counts vary through the day, and an illness, hard exercise or stress can shift them for a short time. ARUP advises drawing at about the same time of day for serial results.

Any time, but try to draw at about the same time of day each time so results are easier to compare. Can shift within days during an illness or after steroid medicines, and usually recovers over weeks. Changes from treatment of a long-term condition build over months.

When to talk to a clinician

A CD8 percent result is not an emergency by itself. Talk with your clinician if it is low or high along with repeated or unusual infections, unexplained fever, night sweats or weight loss. Seek care promptly if you have trouble breathing.

Questions you could ask

  • Which of my lymphocyte results should we follow over time?
  • Could a recent or past infection explain this?
  • Is it high because my CD4 cells are lower?
  • Could a recent illness or a medicine explain this?
  • Does my absolute CD8 count agree with this percent?

Questions people ask

Why look at the percent and the count?

The percent shows the mix of your lymphocytes and the count shows how many CD8 cells you have. A percent can move because other cell groups changed, so the count adds context.

Show the science and sources

For clinicians and researchers

CD8 percent is CD3+CD8+ events as a percent of lymphocytes, with the lymphocyte gate commonly defined by CD45 and side scatter. As a proportion, it rises when another subset, particularly CD4 cells, falls, so it can change without any change in the absolute CD8 count. ARUP reports CD3, CD4 and CD8 as percent of total lymphocytes. ARUP's adult interval is 15% to 46% (ages 16 to 64) and 10% to 46% (65 and older). Other labs differ.

LOINC 32518-3 (primary), 8101-8. Specimen: whole-blood.

Sources

  1. Lymphocyte Subset Panel 4 - T-Cell Subsets Percent and Absolute, Whole Blood (test 0095950), ARUP Laboratories
  2. Reference ranges of lymphocyte subsets in healthy adults and adolescents with special mention of T cell maturation subsets in adults of South Florida, Immunobiology (University of Miami) (2014)

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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