CD16+/CD56+ NK Cells, absolute
How many natural killer (NK) cells are in a microliter of blood. NK cells are white blood cells that help the body handle viruses and damaged cells.
AI-verified against cited sources. Awaiting expert reviewAlso called Abs NKLOINC 9728-7
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What it is
NK cells are a type of lymphocyte, a kind of white blood cell. Unlike T cells and B cells, they can act quickly without having met a germ before. They help clear cells that are infected with viruses and some damaged cells. A lab counts them with flow cytometry, which sorts cells by the proteins on their surface. NK cells lack the T-cell marker CD3 and carry CD56, CD16 or both. This page covers the absolute count, shown as cells per microliter of blood.
Why it matters
NK cells are one part of a lymphocyte subset panel that also counts T cells and B cells. Clinicians use the panel to see how the immune system is built, often when someone has repeated or unusual infections or when an immune problem is being looked into. One NK result rarely points to a single cause, so it is read together with T cells, B cells, a complete blood count and your symptoms.
If it’s low
A low NK 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 is part of an inherited immune condition.
Common causes
- Recent illness or physical stress
- Medicines that affect the immune system, such as corticosteroids or chemotherapy
- A low total lymphocyte count
- Some inherited immune conditions, for example GATA2 deficiency, where B cells and NK cells are both low
- A sample that waited too long before testing
What can help
- Ask your clinician whether a medicine or a recent illness could explain the result
- Ask whether repeating the test in a few weeks makes sense
If it’s high
A high NK count is often not a concern on its own. It can happen for a while during or after a viral infection, or it can simply be your normal. If it stays high on repeat tests, a clinician may look further.
Common causes
- Normal variation between people
- Recent or ongoing viral infection
- Recovery after an illness or a change in immune treatment
- Rarely, a blood condition that makes too many NK-type cells
What can help
- Ask your clinician whether to repeat the test after any recent illness has passed
- Bring your other blood counts to the visit so they 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+24–406 cells/µL
Sources: Labcorp, ARUP Laboratories, EJIFCC (International Federation of Clinical Chemistry and Laboratory Medicine)
Children and teens 9 ranges
- under 0.019100–1,900 cells/µL
Source: Labcorp
- 0.019–-0.833200–1,400 cells/µL
Source: Labcorp
- 0.167–-0.583100–1,300 cells/µL
Source: Labcorp
- 0.417–-0.25100–1,000 cells/µL
Source: Labcorp
- 0.75–0.25200–1,200 cells/µL
Source: Labcorp
- 1.25–1100–1,400 cells/µL
Source: Labcorp
- 2–4100–1,000 cells/µL
Source: Labcorp
- 5–990–900 cells/µL
Source: Labcorp
- 10–1570–1,200 cells/µL
Source: Labcorp
See NK 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 and chemotherapy
- 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
- How the lab defines NK cells (CD3-CD16+CD56+ or CD3-CD56+)
- 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 and other medicines that affect the immune system can change counts.
- Counts calculated from a separate CBC lymphocyte count inherit that count's variation.
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 NK 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 T-cell and B-cell results?
- Could a recent infection explain this count?
- Should we repeat the test or look at my other blood counts?
- Could a medicine or a recent illness explain this result?
- Should we repeat it, and do my T-cell and B-cell counts look as expected?
Questions people ask
Does a normal NK count mean my NK cells work well?
Not necessarily. This test counts the cells. It does not show how well they kill target cells. Special function tests exist, but they are ordered only in specific situations.
Why does my report say CD16/CD56 instead of NK?
NK cells carry the CD16 and CD56 proteins and lack CD3, so labs often name the group by those markers. Labs use slightly different marker combinations, so their ranges differ.
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 NK cells (absolute) unit converter
For clinicians and researchers
NK cells are CD3-negative lymphocytes that express CD56 and/or CD16. Most panels define them as CD3-CD16+CD56+, while Labcorp's table (test 505370) lists CD3-CD56+. Absolute counts come from single-platform bead-based flow cytometry or are calculated as the NK percentage times the CBC absolute lymphocyte count (dual platform), which carries the CBC's variation. 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). ARUP counts cells with CD16 or CD56 (or both) and no CD3. A basic T, B and NK panel is the usual first flow cytometry step in the work-up of suspected primary immunodeficiency (Salzer 2019). Low B and NK counts together with monocytopenia should raise suspicion for GATA2 deficiency (Salzer 2019). Counts do not measure NK function, which needs separate cytotoxicity or CD107a degranulation assays. 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 9728-7 (primary), 20402-4, 53936-1, 20604-5. 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.