FDA/USP Gel Clot

Turbidimetric Testing

Microtest turbidimetric testing aims to detect endotoxin found on medical devices or in drugs. Bacterial endotoxin is cell wall material from Gram-negative bacteria; itís pyrogenic, meaning it can cause high fevers in humans.

Note that Microtest endotoxin assays include turbidimetric plus gel clot and chromogenic methods. All are sensitive, reliable, efficient, and usually recommended over the older, slower pyrogen test using rabbits. Call Microtest for information on which test best suits your particular product and on standard protocols for sample preparation, shipment, and packaging.

As with all Microtest procedures, testing is performed by experienced microbiologists with state-of-the-art equipment. Our method follow procedures derived from the U.S. Food and Drug Administration (FDA) and United States Pharmacopeia (USP). Guidelines on end-product tests for endotoxin content are issued by the FDA and the Center for Devices and Radiological Health (CDRH) under 21 CFR Section 10.90 (b).

Turbidity testing determines the cloudiness of a solution by measuring the loss of intensity in a light beam passing through that solution. In this case, the solution includes as one ingredient the reagent LAL Pyrotell-T. Limulus Amebocyte Lysate (LAL) derives from an unusual biologic source: the circulating amebocytes associated with the blood-clotting mechanism of the horseshoe crab Limulus polyphemus.

In testing, a product sample is washed and the resulting eluate mixed with the LAL reagent to form a solution. This solution is then illuminated via spectrophotometer. If a clotting reaction has caused the solution to become cloudy, the instrument detects a characteristic lessening of light intensity: endotoxin must be present, and the sample fails the test.

Test sensitivity depends on the specific lysate used. Turbidimetric testingís lowest limit of detection (LLD) is 0.005 EU/mL, as compared to 0.03 EU/mL for the gel clot and 0.005 EU/mL for the chromogenic method.

Given the potential for patient harm, all Microtest endotoxin testing procedures are rigorous. Glassware used is controls-checked, and depyrogenated under our extensive Good Manufacturing Practices (GMP) program. Routine tests are run in duplicate, with inhibition/enhancement testing in triplicate. And the Control Standard Endotoxin (CSE) is tested against the USP Endotoxin Reference Standard (RSE).

Test results can usually be reported within 1 week.


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