Horseshoe crab’s blood has a special blue color due to the presence of hemocyanin that transport oxygen throughout the horseshoe crab’s body.
The critical component of the reagents used in endotoxin tests is derived from cells (amebocytes) found in the blue blood of the horseshoe crab, Limulus polyphemus. The lysate of these amebocyte cells, Lymulus Amebocyte Lysate or LAL, contains the proteins of the blood clotting mechanism. This clotting mechanism reacts to antigens found negative bacteria known as lipopolysaccharides (LPS) or endotoxins. In vivo, the formed clot isolates invasive bacteria, and protects the crab from infection. The blood also begins a healing process similar to ours where we form a clot, a scab, and eventually wounds heal.
The LAL reagents are prepared from blood obtained by collecting adult horseshoe crabs and extracting a portion of their blood. The process is very similar to when people donate blood. The crabs are checked for good health, placed in a very clean laboratory, where a small portion of the blood is collected carefully with a sterile needle.
The LAL test is the most sensitive, accurate and cost effective test on the market today to detect contaminating endotoxins. This test was first licensed by the FDA in the 1970’s, and is still the gold standard. It can detect endotoxin in the parts per billion. That’s like finding a grain of sand in an Olympic swimming pool.
The blood coagulation process in the LAL reagent, activated by endotoxins, can be monitored visually in the laboratory using the gel clot method or can be recorded photometrically using a turbidimetric or chromogenic method.