4-(hydroxymeruri)benzoic acid (PHMB) is used to inhibit cystein-protease and acts as a reversible thiol-specific blocker. While blocking the Acylated Ghrelin degradation, it allows the AcetylCholine Esterase AChE T used in SPI-Bio EIA kits to work normally, in contrary to serine-protease inhibitors. Neuropeptides and other short peptides are really sensitive to protease degradation. It is often necessary to add specific and potent inhibitor to avoid total loss of the biomarker. The PHMB containing tubes have been designed to accept 1 mL samples. The tubes are graduated, with a silicone washer sealed and external threads. They can be stored at temperatures as low as -80 degrees. Thus, PHMB sampling tubes may be useful to measure any biomarker cleaved by cystein-proteases.