NK Cells Cytotoxicity Assay

The NK Cells Cytotoxicity Assay is a specialised immunological investigation used in reproductive medicine to assess whether natural killer (NK) cells in the uterine environment are exhibiting excessive cytotoxic activity against early embryonic tissue. It is most often requested for women with a history of recurrent implantation failure, recurrent miscarriage, or unexplained infertility, where a dysregulated immune response is suspected as a contributing factor. The assay is performed using flow cytometry, a technique that identifies and quantifies specific cell populations and their functional activity with high precision.

Natural killer cells are a type of lymphocyte that normally play a vital role in defending against infection and in early pregnancy, where they help remodel the uterine blood vessels to support placental development. However, when these cells become overactive or their cytotoxic potential is abnormally elevated, they may target the developing embryo, potentially disrupting implantation or leading to early pregnancy loss. This test evaluates both the proportion and the functional cytotoxicity of NK cells, providing a clearer picture of the immune environment that may be affecting fertility outcomes.

What is measured

• NK cell cytotoxicity (activity): how actively your natural killer cells kill target cells in the laboratory, measured at several cell ratios and reported as a percentage against a typical range.
• Effect of intralipid (laboratory test): the report also examines whether intralipid, a substance sometimes used in fertility clinics, reduces this cell-killing activity in the test tube.

Why it matters

For couples navigating recurrent implantation failure or unexplained miscarriage, the emotional and physical toll is immense. Identifying an immunological cause such as elevated NK cell cytotoxicity can provide a concrete explanation and open the door to targeted therapeutic options, including immunomodulatory treatments. This assay offers clinicians the evidence needed to personalise fertility care, moving beyond trial and error towards a more precise, immune-informed approach that may improve the chances of a successful pregnancy.