USP <85> Endotoxin Testing

USP <85> endotoxin testing detects endotoxin levels in medical devices. Endotoxin testing typically occurs at the batch release stage to ensure that medical devices are free of dangerous endotoxins, which, when introduced into contact with a patient, can cause fever, meningitis, hemorrhagic shock, blood pressure drop, and other dangerous effects.

Per USP <85> endotoxin testing standards, endotoxin levels in a product must register below 0.5 EU/mL at the time of batch release testing in order to be considered acceptable and safe. The USP <85> bacterial endotoxins test applies to any product that contacts intravascular, intrathecal, intraocular, or intralymphatic patient systems.

Medical device endotoxin testing is conducted using Limulus amebocyte lysate (LAL), an extract of blood cells from the Limulus polyphemus horseshoe crab. This extract is known to react to endotoxins in a measurable, repeatable way, and is thus the most consistent testing method readily available for gram-negative bacteria. There are three methodologies for which LAL can be used: gel-clot testing, turbidmetric testing, and chromogenic testing.

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Gel-clot Endotoxin Testing

In gel-clot testing or gel-clot assay, LAL undergoes a clotting response as a reaction to the presence of endotoxins. This is essentially the same reaction that would occur in the horseshoe crab source of LAL if injured. In this test, the sample is added to a test tube containing LAL, which will either coagulate and form a clot in the presence of endotoxin, or will run freely down the sides of the test tube when turned upside down if no endotoxins are present.

Gel-clot testing is primarily recommended for low-volume testing. It is the only test fully described in the USP, and is generally considered to be the primary required endotoxin test. If gel-clot testing is not possible or is not practical or viable, the following methods may also be acceptable alternatives.

Turbidimetric Endotoxin Testing

For higher volume testing, the turbidimetric test may be more practical. The coagulation response in LAL remains the indicator of endotoxin presence, but in this test, the rate of turbidity increase as coagulation occurs is used to measure the total endotoxin concentration in the sample. Either the endpoint turbidimetric method or the kinetic turbidimetric method may be used.

Chromogenic Endotoxin Testing

In chromogenic testing, a reagent is added to the LAL. Once the sample is added, if endotoxins are present, they will initiate the clotting reaction, which will cause the reagent to change color at a rate corresponding to the concentration of endotoxin. Endpoint and kinetic chromogenic testing are available.

In general, gel-clot testing is most suitable for low volume endotoxin testing and scenarios where positive/negative results are required. Turbidimetric and chromogenic testing are better suited for higher-volume testing scenarios, and those where the concentration of endotoxin must be recorded. BA Sciences maintains a deep stable of knowledge in medical device and pharmaceutical testing, including USP <85> testing and many other standards and requirements that your application may require. We are ready to work with you to help you choose the correct method and achieve accurate, certifiable results.

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