The creatures’ copper-rich blood clots in the presence of bacterial endotoxins and has long been used in tests to detect contamination in shots and infusions.

More recently, human-made versions called recombinant Factor C (rFC) from Basel-based Lonza and others have emerged.

Maryland-based US Pharmacopeia (USP), whose influential publications guide the drug industry, had initially proposed adding rFC to the existing chapter governing international endotoxin testing standards.

USP has now abandoned that, it announced late on Friday, opting instead to put rFC in a new stand-alone chapter. This means drug companies seeking to use it must continue to do extra validation work, to guarantee their methods of using rFC tests match those of tests made from horseshoe crab blood.

The decision gives the drug industry fewer incentives to end its reliance on animal-based tests, even as companies like Lonza and France’s bioMerieux promote human-made alternatives, and wildlife advocates worry about horseshoe crab bleeding’s effect on the coastal ecosystem.