Horseshoe crab blood is rare but crucial for medicine, so this scientist came up with a solution

The rarest blood is blue.

Jeak Ling Ding, molecular biologist at the National University of Singapore // As told to Rachel Nuwer

Horseshoe crabs are crucial participants in modern medicine. This 500-million-year-old species’ bright blue blood will clot in the presence of bacterial toxins that can cause septic shock in humans. Pharmaceutical companies use the stuff to test intravenous medications for these clot-causing substances before the drugs enter our bodies. They use it so much in medicine that horseshoe crab populations are at risk.

In the 1980s, my team sought to create a synthetic version of the gene responsible for this clotting reaction. We needed specimens to learn from, so we traveled to an estuary on Singapore’s northern coast and went into the mud to collect crabs. Oh my god, that sludge was stinky! Back in the lab, we took a few milliliters of blood, and then safely ­returned the animals to the water. Drug companies must drain far more blood, and many crabs die once back in the sea.

My lab began selling our synthetic alternative in 2004, but companies still use the animals’ blood. Changing the status quo takes work—I hope that will change soon.

This article was originally published in the Summer 2019 Make It Last issue of Popular Science.