The Horseshoe Crab's Miracle Blood

Although the horseshoe crab is considered a living fossil, its blue blood provides modern medicine with a substance that is crucial for drug testing.

Although horseshoe crabs have remained relatively unchanged for over 250 million years this living fossil of a creature now provides modern science with a substance crucial for saving thousands of lives. This is the miracle blue blood of the horseshoe crabs. Unlike the red blood of other animals which contains iron, the horseshoe crab's blood has copper in it which is what makes their blood blue in color. But it is not the color of the horseshoe crab's blood that makes it remarkable. It is the fact that this blood will quickly clot when it comes into contact with even the minutest impurities. This is what makes the horseshoe crab's blood truly miraculous since it is the only substance known which can so effectively detect impurities.

A scientist named Frederick Bang first discovered this clotting quality of the horseshoe crab's blood in the 1950s. What led Bang into his experiments with the horseshoe crab's blue blood was how quickly its blood clots when receiving a wound. Bang isolated the chemical in the horseshoe crab's blood that caused the clotting and called it "Limilus amoebocyte lystate" or LAL. This LAL is now used to test all drugs that are used intravenously such as vaccines. Because only a small amount of LAL can be obtained from the horseshoe crab's blood, it is extremely rare, costing up to $15,000 per quart.

Before the discovery of LAL by Dr. Bang, the method of detecting impurities in drugs was rather crude. It consisted simply of injecting the drug being tested into a rabbit. If the rabbit got sick or died then the drug was discarded. This was hardly an effective test and contaminated drugs often went undetected and caused harm in patients receiving such drugs. So effective is LAL in detecting impurities in drugs that the FDA since 1987 requires it for testing all drugs to be used by humans. One interesting thing about LAL is that despite intensive efforts to make it synthetically, the only source for this vital product is still the blue blood of the horseshoe crab.

Despite the fact that the horseshoe crab's blood is so vital to medical science, much of the horseshoe crab's population is being depleted due to over-harvesting. Fishermen have found that horseshoe crabs make excellent bait for conch and eels. Most of the horseshoe crabs are found in the North Atlantic, with the bulk of them in the Delaware Bay area. As a result, states in that region have reduced by 25 percent the numbers of horseshoe crabs that can be harvested. As to the horseshoe crabs that are used for medical purposes, needles are used to draw their blood out of them. When approximately one-third of their blood is withdrawn, the horseshoe crabs are returned to the water. They will then survive to perhaps one day supply yet more of their precious blue blood to medine.

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