Study design and population
This study was conducted with women admitted to the Seoul National University Bundang Hospital between March 2019 and March 2020. Pregnant female volunteers were recruited for this study. The case group included women diagnosed with PE; and the control group consisted of women who did not present with PE or kidney disease up until delivery. After obtaining informed consent, we collected urine samples (15 ml) at admission from women diagnosed with PE and at the time of hospitalization for delivery from the normal control group. Spot urine samples were stored at 4 °C immediately after collection and tested within 48 h. The calculation of the number of target participants was based on a specificity of 92%, according to the literature on the number of samples required for the performance evaluation of the diagnostic kit. The formula for the calculation is as follows:
\begin{equation} N=P\ \times\left(1-P\right)\times\left(\frac{\mathcal{Z}_{\frac{a}{2}}}{d}\right)^{2}\nonumber \\ \end{equation}
When the margin of error (d) is calculated as 0.08, at the significance level α=0.05, the minimum number of participants required to show a specificity of 92% or higher according to the above formula is 44. Considering a 15% dropout rate, 51 patients were required per group. The results of the point-of-care test were compared (between the 2 groups) using the exact concentration of nephrin by enzyme-linked immunosorbent assay (ELISA). The ELISA assay was performed twice to measure the concentration of nephrin protein using the Human Nephrin DuoSet® ELISA Kit (R&D Systems, Minneapolis, MN, USA) according to the manufacturer’s instructions. This study was approved by the Institutional Review Board of the Seoul National University Bundang Hospital (IRB No. B-1904/537-304).