An ELISA method detecting the active form of suPAR

•This new ELISA assay detects only the active form of suPAR.•Active suPAR is defined as suPAR capable of binding to uPA.•This assay measures active suPAR down to 15 ng/L and has over 100-fold linear range.•The Inter-coefficient of variation (CV) and Intra-CV is 9.6% and 8.5% respectively.•This assay can recover 99.74% recombinant suPAR added to plasma pool.

Urokinase plasminogen activator receptor (uPAR) exists in a number of formats in human plasma, including soluble uPAR (suPAR) and uPAR fragments. We developed an ELISA method to detect specifically the active form suPAR, which binds to its natural ligand uPA. The intra CV and inter CV of this ELISA assay is 8.5% and 9.6% respectively, and the assay can recover 99.74% of added recombinant suPAR from 10% plasma. This assay is quite sensitive, capable of detecting down to 15 pg/ml of suPAR, and can measure suPAR concentrations in the range of 0.031–8 ng/ml with high linear relationship. Plasma samples from pregnant women were also measured for the active form of suPAR with this assay, giving an averaged level of 1.39 ng/ml, slightly higher than the level of pooled plasma from healthy donors (0.96 ng/ml). This study demonstrates the feasibility to measure the active form of suPAR, which will likely have value in clinical applications.

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