Endotoxin Kits FAQ
What is Endotoxin?
How do I convert EU/ml to ng/ml of endotoxin?
Which endotoxin detection method should I choose?
What is the maximum acceptable endotoxin level?
Endotoxin is a complex lipopolysaccharide (LPS), found on the outer membrane of most pathogenic Gram-negative bacteria. Although boiling for 30 minutes does not destabilize endotoxin, it can be degraded by certain powerful oxidizing agents, such as superoxide, peroxide and hypochlorite.
Endotoxin Units (EU), rather than units of weight, is a measure of the activity of endotoxin. It was developed by the FDA for comparison testing because the potency of endotoxin depends on a variety of factors: polysaccharide chain length, aggregation, solubility in biological fluids, bacterial source, associated substances, etc. Expressing endotoxin concentrations in EU addresses the issue of different potencies of different endotoxins.
Please use the following example to convert your endotoxin level: 10 EU/mL = 1.0 ng/mL
Three things to consider before choosing an endotoxin detection method: the type of sample to be tested, its interference characteristics, and the endotoxin limit that you want to detect. The Gel-clot method is the simplest and most widely used method for endotoxin detection, and its sensitivity is up to 0.03 EU/ml. The Chromogenic method defines its sensitivity to be the lowest endotoxin concentration in the standard curve and requires a spectrophotometric instrumentation to read the results.
One EU is approximately equivalent to 100 pg of E. coli lipopolysaccharide—the amount present in approximately 105 bacteria. Humans can develop symptoms when exposed to as little as 5 EU/kg body weight. These symptoms include, but are not limited to, fever, low blood pressure, increased heart rate, and low urine output. Even small doses of endotoxin in the blood stream are often fatal.
The FDA has set the following maximum permissible endotoxin levels for drugs distributed in the United States:
- Drug (injectable, intrathecal) - 0.2 EU/kg body weight
- Drug (injectable, non-intrathecal) - 5 EU/kg body weight
- Sterile water - 0.25-0.5 EU/ml (depends on intended use)
Does any substance interfere with the binding of endotoxin to endotoxin Removal Resin?
Yes. Other detergents and high levels of chaotropes (urea and guanidine) can reduce the affinity of Polymixin B for LPS. Proteins such as BSA can bind tightly to endotoxin, reducing its ability to interact with and bind to the endotoxin Removal Resin. This reduction in binding capacity can sometimes be overcome by increasing the volume of immobilized polymixin B. However, some proteins bind tightly to endotoxin without inhibiting its binding to ligands. In this case, the protein will remain bound to the resin with the endotoxin, possibly causing a loss of the protein of interest.