2.6. Measurement of Serum sCD40L Levels
Serum samples for the measurement of sCD40L levels were obtained at a median interval of 23 days (interquartile range (IQR): 13–43.5 days) following the surgical procedures, and immediately preceding the commencement of vitamin D/placebo supplementation. These serum specimens were aliquoted in 0.5 mL portions to avoid frequent thawing and refreezing, and stored at a temperature of −80 °C until their utilization in subsequent analyses.The quantification of serum sCD40L levels was performed by a member of the research team who conducted the measurements without any prior knowledge of the randomized group assignments or the patients’ clinical information, including their predetermined outcomes, which were established prior to the initiation of statistical analyses.A Human CD40L ELISA Kit (TNFSF5) (ab196268) (Abcam, Cambridge, MA, USA) was used according to the manufacturer’s protocols. The lower limit of detection of serum sCD40L of the ELISA kit was 2.9 pg/mL. The 294 samples in which sCD40L was measured were divided into tertile groups based on sCD40L levels, with boundaries set at 83.35 pg/mL and 165.76 pg/mL.