This ELISA kit provides quantitative detection of Cathepsin L, a potent cysteine protease released during CHO cell culture. Its high sensitivity supports monitoring of Cathepsin L in culture supernatants, purification intermediates, and final product assessments. The assay’s optimized reagents and pre‑coated microplate ensure reproducible performance across runs. E‑65CTL is well suited for HCP profiling, process optimization, and risk assessment of protease‑mediated degradation in therapeutic protein production.