NCAM1 and cholesteryl ester measurement: In addition to the lack of consensus as to the number of plasmatic cells necessary to make a CE diagnosis, which varies from a single one to a minimum of five plasma cells, a significantly lower percentage of NK cells in CE patients has been found compared with control patients: indeed, the expression of CD56+ CD16− and of CD56bright CD16−, markers of NK cells, was significantly lower (47.8% ± 18.6 and 30.1% ± 20.5 vs 79.5% ± 3.9 and 67.3% ± 8.1, respectively; p < 0.01) when compared to unexplained infertile women without any sign of CE [14, 15].