Platform
Company
Immunology & Autoimmune
Review status
Currently under review
Pending specialist review and validation.
This test measures the proportion of your white blood cells that are natural killer (NK) cells, identified by the surface markers CD16 and CD56. Laboratories use CD45 to first identify white blood cells, then apply flow cytometry to detect the NK cell markers. The result is reported as a percentage, showing how large the NK cell group is compared with other lymphocytes.
NK cells are part of your innate immune system. They help control viral infections and abnormal cells by recognizing and killing targets without prior sensitization. This test is often included in lymphocyte subset panels and may also be ordered alone when your clinician wants a focused look at NK cells.
Your NK cell percentage can provide clues about how your immune system is functioning. Lower or higher proportions can occur in certain inherited or acquired immune conditions, during or after infections, and with some blood cancers. It is also monitored when you receive medicines that affect the immune system, and after stem cell or organ transplant as part of immune reconstitution follow up.
Clinicians interpret this result alongside your symptoms, medical history, examination, and other laboratory tests. It can help evaluate frequent or unusual infections, unexplained changes in lymphocytes, and some autoimmune conditions, and it can inform treatment decisions in selected cases.
Results are interpreted using age-specific expectations, because NK cell proportions change across infancy, childhood, and adulthood. The percentage reflects a share of cells, not a direct count; some clinicians also consider the absolute NK cell count, which is derived by combining this percentage with your white blood cell and lymphocyte counts.
Temporary shifts can occur with viral illnesses, vaccines, physical or emotional stress, vigorous exercise, pregnancy, or medications. An unexpected result often leads to repeat testing when you are well, or to additional studies such as a complete lymphocyte subset panel or functional NK cell testing. Discuss your result with your clinician, who will consider your overall health to decide on next steps.
Reference intervals vary by laboratory, analyzer, methodology, population, and units. The ranges shown here are for education only. Always interpret your results against the reference interval printed on your own lab report.
Flow cytometry specimens should be processed promptly; delays, improper storage temperature, or use of the wrong tube can degrade cell markers and skew the measured percentage.
A current or recent viral illness, or a recent vaccine, can temporarily raise or lower NK cell proportions as your immune system responds and recovers.
Corticosteroids, calcineurin inhibitors, chemotherapy, biologic agents, and cytokine therapies can alter NK cell distribution or marker expression, affecting the result.
Intense exercise, acute stress, or sleep deprivation can shift circulating NK cells for several hours, so timing of the blood draw relative to activity can influence the value.
Physiologic immune changes during pregnancy and shortly after delivery can influence NK cell measurements; interpretation may differ in this setting.
NK cell percentages vary with age and may show diurnal patterns, so your age and the time of day the sample was collected can affect the result.
References