Any fluid, which is going to be injected into the bloodstream, must be free of pyrogens. Pyrogens are bacteria or even bits of dead bacteria which can cause a toxic reaction or fever when introduced into the blood. Testing for pyrogens used to be carried out by injecting the test fluid into a rabbit and seeing if its body temperature rose. A test for pyrogenicity has now been developed, validated and accepted by the regulatory authorities. This uses blood from the horseshoe crab.
Some blood is taken from the crab, which is then returned to wild unharmed.
The blood from one crab replaces several rabbits. The LAL test is not perfect and work is continuing to develop a method which uses diluted, whole human blood.