RESUMEN
Natural killer (NK) cell assessment has been attempted since the 1990s and, apart from antibody testing, is probably the commonest immune test available to clinicians. It is clear that simple enumeration of uterine NK cells by immunohistochemistry is inadequate, although better methodology such as flow cytometry may prove to be more beneficial in the future. Blood testing is an appealing noninvasive test that may be a marker for immune dysfunction, rather than a guide to uterine numbers per se. It is currently performed in women with repeated reproductive failure and should be done using tests of activation. Patients value investigation and clinicians should prefer it to blind empirical immune therapy in repeated reproductive failure cases. But, in addition to blood NK testing, a fundamental new NK genetic test (the KIR/HLA-C interaction) is likely to provide an even more effective diagnostic tool. Insights from KIR/HLA-C analysis imply that new immune therapy trials will need to take KIR/HLA-C results into account.