What Is Endotoxin (LAL) Testing?
Short answer
Endotoxin testing checks a product for bacterial endotoxins, fever-causing molecules from the outer membrane of Gram-negative bacteria. The standard method is the LAL test, which uses Limulus amebocyte lysate made from horseshoe crab blood cells; it reacts with endotoxin by clotting or producing a measurable signal. It is a key release test for sterile products and pharmaceutical water.
What endotoxins are and why they matter
Endotoxins are lipopolysaccharides (LPS) from the cell walls of Gram-negative bacteria. They are released when bacteria die or break apart, and they are heat-stable, so sterilizing a product kills bacteria but does not necessarily remove endotoxin. That is why a product can be sterile and still contain endotoxin. In products introduced into the body, endotoxin can cause fever and other reactions, which is why regulators expect endotoxin testing of sterile products (FDA).
How the LAL test works
Horseshoe crab blood cells (amebocytes) contain a clotting system that is triggered by endotoxin. Lysate made from those cells, Limulus amebocyte lysate, is mixed with the sample. If endotoxin is present, the reaction proceeds, and the lab reads it in one of three main ways (FDA):
| Method | How it reads | Result type |
|---|---|---|
| Gel-clot | Forms a firm gel when endotoxin is above the test’s sensitivity | Pass/fail (limit test) |
| Kinetic turbidimetric | Measures increasing cloudiness over time | Quantitative |
| Kinetic chromogenic | Measures color released from a synthetic substrate | Quantitative |
Results are reported in endotoxin units (EU) per mL or per unit of product and compared with the product’s limit. Labs also run positive product controls to confirm that the sample itself doesn’t inhibit or enhance the reaction.
Who needs endotoxin testing
- Compounding pharmacies and 503B outsourcing facilities releasing sterile preparations. See compounding pharmacy testing.
- Manufacturers of sterile products, components and packaging, alongside sterility and other microbiology tests (FDA aseptic processing guidance).
- Water systems producing pharmaceutical-grade water, together with TOC and conductivity monitoring.
What a lab needs from you
To quote endotoxin testing, we need the product or water type, its intended use, the endotoxin limit you are working to (if you have one), the number of samples and how the samples will be packaged. Endotoxin sticks to some plastics and glass, so we tell you which containers to use before you collect samples.
Endotoxin testing at Renew Lab Group
Our Houston lab offers endotoxin testing by the LAL method together with microbiology, ICP-MS, TOC and extractables/leachables testing; see our HPLC lab testing services. We also use it on our own products: every batch of our Bacteriostatic Water and Sterile Water for Injection is made in our cleanroom and tested for endotoxin and sterility, and a Certificate of Analysis is run monthly covering each production batch (research use only). To request testing, call 936-379-5515 or email info@renewlabgroup.com.
Related questions
Is endotoxin testing the same as sterility testing?
No. Sterility testing looks for living microorganisms. Endotoxin testing detects heat-stable bacterial toxins that can remain even after a product is sterilized.
What is the difference between gel-clot and kinetic LAL?
Gel-clot is a pass/fail limit test read by whether a gel forms. Kinetic turbidimetric and chromogenic methods measure a signal over time and give a quantitative result.
What does EU/mL mean?
Endotoxin units per milliliter, the standard unit for reporting endotoxin. Results are compared with the limit for the specific product.
Can you test my product for endotoxin?
Tell us the product and its use, and we’ll confirm the method and a quote. Call 936-379-5515 or email info@renewlabgroup.com.
Talk to the lab about endotoxin (LAL) testing
Tell us what you need tested and we’ll recommend a method and send a quote. Contact us at 936-379-5515 or info@renewlabgroup.com for current pricing, turnaround and sample requirements. Samples can be dropped off at our lab at 6001 Central Crest, Houston, TX 77092.
Sources
Researcher resources
- Shop Bacteriostatic and Sterile Water
- View Our Certificate of Analysis
- Free Reconstitution Calculator
- Compare BAC Water Products
Keep reading
- What Is a Beyond-Use Date (BUD)?
- Can You Use Tap Water in an Ultrasonic Diffuser?
- What Is ICP-MS Testing?
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