Lecarpentier E, Zsengellér ZK, Salahuddin S, et al. - Preeclampsia is characterized by elevated circulating sFLT-1 (soluble fms-like tyrosine kinase) and low levels of its ligand, PlGF (placental growth factor). Researchers examined if decreased placental production of PlGF or binding of PlGF by increased circulating sFLT-1 results in the low levels of plasma PlGF noted during preeclampsia. They delineated a biochemical procedure to dissociate PlGF-sFLT-1 complex ex vivo in this study and when used along with an immunoassay platform, demonstrate a method to determine total and free PlGF in human blood samples. Using this method, they identified significantly lower plasma free PlGF levels in preeclampsia (N = 22) than in nonhypertensive controls (N = 24; mean, 314 vs 686 pg/mL), but there were no differences in total PlGF levels (mean, 822 vs 800 pg/mL). In contrast, significantly higher total sFLT-1 levels were observed in preeclampsia than in nonhypertensive controls (mean, 16,957 vs 3,029 pg/mL) and there was correlation of sFLT-1 levels with bound PlGF levels (bound PlGF = total PlGF−free PlGF) in these samples. In conjunction with previous studies, findings from this study yield evidence that reduction in circulating PlGF noted during preeclampsia is largely mediated by excess circulating sFLT-1.