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CD3+ T Cells, percent

The share of your lymphocytes that are T cells, which carry a marker called CD3. The absolute count is usually more useful.

AI-verified against cited sources. Awaiting expert reviewAlso called CD3 pctLOINC 20599-7

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What it is

Lymphocytes are a type of white blood cell. T cells are the lymphocytes that coordinate the immune response and attack infected cells, and they are identified by a marker called CD3. This result is the percent of all your lymphocytes that are T cells, measured by flow cytometry. It comes from the same blood sample as the CD4 and CD8 results, which are the two main groups of T cells.

Why it matters

The percent shows the mix of your lymphocytes, not how many T cells you have. If another group, such as B cells, goes up or down, the T-cell percent moves even when the number of T cells has not changed. For this reason clinicians usually look at the absolute CD3 count first and use the percent as extra context.

If it’s low

A low percent means T cells make up less of your lymphocytes than usual. This can happen when B cells or NK cells are a bigger share, or when T cells themselves are low.

Common causes

  • Natural variation between draws and between labs
  • A higher share of B cells or NK cells, as can happen during some infections
  • A recent acute illness or physical stress
  • Medicines that suppress T cells, such as corticosteroids and chemotherapy
  • Advanced HIV infection (the CD4 and CD8 results give more detail)
  • Rare inherited immune conditions that reduce T cells

What can help

  • Ask your clinician to read it with the absolute CD3 count and the CD4 and CD8 results
  • Share every medicine and supplement you take, including steroids
  • Ask whether repeating the test after you have recovered makes sense

If it’s high

A percent above the lab's range means T cells make up more of your lymphocytes than usual. Often this happens because another group, such as B cells or NK cells, is lower, not because T cells increased.

Common causes

  • Natural variation between draws and between labs
  • A lower share of B cells or NK cells, which makes T cells a bigger share
  • A recent viral infection, such as infectious mononucleosis, which can raise T-cell numbers for a while
  • Rarely, a blood disorder involving T cells

What can help

  • Ask your clinician to read it with the absolute CD3 count and the other lymphocyte 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 CD3 % 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
  • Acute illness, stress and medicines such as corticosteroids
  • The other lymphocyte groups: because this is a share of all lymphocytes, a change in B or NK cells moves it too
  • 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 CD3 percent result is not an emergency by itself. Talk with your clinician if it is low along with repeated or unusual infections, unexplained fever 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?
  • Is this high because another group of lymphocytes is lower?
  • Should we repeat it in a few weeks?
  • Could a recent illness or a medicine explain this?
  • What does my absolute CD3 count show?

Questions people ask

Is the percent or the absolute count more useful?

The absolute count is usually more useful because it shows how many T cells you have. The percent shows the mix of your lymphocytes. Reading both together gives the clearest picture.

Why does my lab's range differ from the one on this page?

Labs set intervals from their own methods and reference groups. ARUP's adult range is 62% to 87%, and other labs can differ a little. Compare your result with the range printed on your own report.

Show the science and sources

For clinicians and researchers

CD3 is part of the T-cell receptor complex and is present on all mature T cells, so CD3+ lymphocytes are total T cells (CD4+, CD8+ and the smaller double-negative and NK-T populations). The percent is CD3+ events divided by the lymphocyte gate, which is commonly defined by CD45 and side scatter. T, B and NK cells together make up nearly all lymphocytes, so a rise or fall in B or NK cells shifts the CD3 percent even if the absolute T-cell count is stable. ARUP reports CD3 percent as a percent of total lymphocytes, with an adult interval of 62% to 87% (ages 16 to 64) and 62% to 89% (65 and older). Other labs differ.

LOINC 20599-7 (primary), 8124-0. 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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