While studies did find a correlation between TREM2 expression on blood monocytes and an AD diagnosis [128], sTREM2 in plasma was shown to not correlate with CSF sTREM2 levels [86] and plasma samples yielded non-significant differences in sTREM2 of AD and FTD patients compared to healthy controls [86, 225]. This evidence concerns the gene TREM2 and Alzheimer disease.