CD3+ T Cells, absolute
How many T cells are in a microliter of blood. T cells are white blood cells that direct and carry out much of the immune response.
AI-verified against cited sources. Awaiting expert reviewAlso called Abs CD3LOINC 8122-4
Check your result
Type your result to see where it falls.
Nothing you type here leaves your browser.
What it is
T cells are lymphocytes, a type of white blood cell. Some help coordinate the immune response, and others destroy infected cells. Labs count them with flow cytometry by looking for the protein CD3, which every T cell carries. The CD3 count is the total of the helper (CD4) and cytotoxic (CD8) groups plus smaller T-cell groups. This page covers the absolute count, shown as cells per microliter of blood.
Why it matters
T cells are central to fighting viruses and many other infections. The T-cell count is the first part of a lymphocyte subset panel, which also counts B cells and NK cells. Clinicians use it when someone has repeated or unusual infections, when an immune problem is being looked into, and to follow some conditions and treatments. It is read together with the CD4 and CD8 counts, the other cell groups and your symptoms.
If it’s low
A low T-cell count means fewer of these cells than usual in the sample. It is often temporary and tied to an illness or to medicines that affect the immune system. Less often, it comes from an infection that affects T cells or from an inherited immune condition.
Common causes
- Recent illness, including some viral infections
- Medicines that affect T cells, such as corticosteroids, chemotherapy or transplant medicines
- A low total lymphocyte count
- HIV infection, which mainly lowers the CD4 group
- Inherited T-cell conditions such as severe combined immunodeficiency, usually found in infancy
What can help
- Ask your clinician whether a medicine or a recent illness could explain the result
- Ask whether the CD4 and CD8 counts and a repeat test would help
If it’s high
A high T-cell count is often temporary, for example during or after a viral infection. It can also be your normal. A count that stays high, or comes with other blood count changes, is something a clinician may look into further.
Common causes
- Normal variation between people
- Recent or ongoing viral infection
- A high total lymphocyte count from any cause
- Rarely, a blood condition that makes too many T cells
What can help
- Ask your clinician whether to repeat the test after any recent illness has passed
- Bring your complete blood count so the results can be read together
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.
- 16+622–2,402 cells/µL
Sources: Labcorp, ARUP Laboratories, EJIFCC (International Federation of Clinical Chemistry and Laboratory Medicine)
Children and teens 9 ranges
- under 0.019600–5,000 cells/µL
Source: Labcorp
- 0.019–-0.8332,300–7,000 cells/µL
Source: Labcorp
- 0.167–-0.5832,300–6,500 cells/µL
Source: Labcorp
- 0.417–-0.252,400–6,900 cells/µL
Source: Labcorp
- 0.75–0.251,600–6,700 cells/µL
Source: Labcorp
- 1.25–11,400–8,000 cells/µL
Source: Labcorp
- 2–4900–4,500 cells/µL
Source: Labcorp
- 5–9700–4,200 cells/µL
Source: Labcorp
- 10–15800–3,500 cells/µL
Source: Labcorp
See T cells (absolute) by age and sex, with the U.S. survey numbers where they exist.
What can affect your result
- Recent infection or illness
- Medicines that affect the immune system, including corticosteroids, chemotherapy and transplant medicines
- Age and sex: counts differ somewhat between groups, and children have much higher counts than adults
- Time of day
- Method: bead-based counts versus counts calculated from a separate CBC lymphocyte count
- How long the sample sat before testing
- The sample must stay at room temperature and reach the lab quickly: Labcorp asks for arrival within 48 hours, and ARUP lists 72 hours in EDTA tubes and 48 hours in heparin tubes. Refrigerated, frozen, hemolyzed or clotted samples are rejected (Labcorp, ARUP).
- Recent infection, corticosteroids, chemotherapy, transplant medicines and other medicines that affect the immune system can change counts.
- Counts calculated from a separate CBC lymphocyte count shift whenever the CBC lymphocyte count shifts.
Counts can shift over the day, so a similar time of day helps when you compare repeat results. Counts can change over days to weeks with illness and over weeks to months after immune-changing treatment.
When to talk to a clinician
Talk with your clinician if you have repeated, severe or unusual infections, or if your T-cell count is well outside your lab's range. Get urgent care for a high fever with shaking chills, trouble breathing, confusion or an illness that is getting worse fast.
Questions you could ask
- Why was this panel ordered for me, and what are you looking for?
- How should I read this alongside my B-cell and NK-cell results?
- Could a recent infection explain this count?
- Should we repeat the test or look at my CD4 and CD8 counts?
- Could a medicine or a recent illness explain this result?
- Should we repeat it, and what do my CD4 and CD8 counts show?
Questions people ask
Is the CD3 count the same as the CD4 count?
No. CD3 counts all T cells. CD4 counts only the helper T cells, which are one part of the CD3 total. The CD8 group is the other large part.
Why is my absolute count different from my percent?
The percent is the share of your lymphocytes that are T cells. The absolute count also depends on how many lymphocytes you have in total, so the two can move in different directions.
Show the science and sources
Units
- 1 cells/µL = 1 cells/µL
- 1 cells/µL = 0.001 ×10³/µL
- 1 cells/µL = 0.001 ×10⁹/L
- 1 cells/µL = 1 ×10⁶/L
Open the T cells (absolute) unit converter
For clinicians and researchers
CD3 is part of the T-cell receptor complex and marks all mature T cells (CD4+, CD8+, double-negative and gamma-delta). Absolute counts come from single-platform bead-based flow cytometry or are calculated as the CD3 percentage times the CBC absolute lymphocyte count (dual platform), so CBC changes shift the result. Reference intervals are lab- and method-specific. Labcorp's adult interval was set by the lab, and its pediatric rows come from Comans-Bitter et al. (J Pediatr 1997). A basic T, B and NK panel is the usual first flow cytometry step for suspected primary immunodeficiency, including SCID (Salzer 2019). In HIV care the CD4+ subset, not total CD3, is the standard monitoring count. Specimen: whole blood at room temperature (Labcorp: lavender EDTA plus yellow ACD tubes, received within 48 hours; ARUP: EDTA, stable 72 hours, or heparin, stable 48 hours).
LOINC 8122-4 (primary). Specimen: whole-blood.
Sources
- T- and B-Lymphocyte and Natural Killer Cell Profile (test 505370), Labcorp
- Flow Cytometry in the Diagnosis and Follow Up of Human Primary Immunodeficiencies, EJIFCC (International Federation of Clinical Chemistry and Laboratory Medicine) (2019)
- Lymphocyte Subset Panel 5 - Total Lymphocyte Enumeration (test 0095892), ARUP Laboratories
AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.