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Medical uses for the Horseshoe Crab
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a bottle of horseshoe crab blood, it is a bright blue color HORSESHOE CRAB BLOOD
The blood of the horseshoe crab provides a valuable medical product critical to maintaining the safety of many drugs and devices used in medical care. A protein in the blood called Limulus Amebocyte Lysate (LAL) is used by pharmaceutical and medical device manufacturers to test their products for the presence of endotoxins, bacterial substances that can cause fevers and even be fatal to humans.

The LAL test is one of the most important medical products derived from a marine organism to benefit humans.

Why is the Horseshoe
Crab the original “blue blood”?
A horseshoe crab’s blood has a blue to blue-green color when exposed to the air. The blood is blue because it contains a copper-based respiratory pigment called hemocyanin.

Additional references...
Updated July 29, 2005