INTER-LABORATORY ANALYSIS OF ENDOTOXIN IN COTTON DUST SAMPLES

Authors: JACOBS, ROBERT - EASTERN VA MED. SCHOOL; Chun, David

Submitted to: American Journal of Industrial Medicine
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/11/2004
Publication Date: 9/1/2004
Citation: Jacobs, R. R., Chun, D. C. 2004. Inter-laboratory analysis of endotoxin in cotton dust samples. American Journal of Industrial Medicine 46:333-337.

Interpretive Summary: To address the question of different laboratories analyzing the same dust samples and arriving wit the same ranking of the samples for endotoxin but not necessarily the same quantitative amount of endotoxin, an interlaboratory two-part round robin endotoxin assay study was conducted. Initial results were the results each laboratory obtained using its normal method of endotoxin analysis. Later results were of filter membranes with cotton dust where the analysis were performed as before but with a common extraction protocol. The intralaboratory results had small variations but the interlaboratory results had very high variations. This held true for both parts of the study; but in the second part of the study, when the extraction protocol was standardized, the interlaboratory results showed reduced differences, which suggested that with further standardization, further reduction of differences between laboratories might be achieved so that results between laboratories would be comparable. A second interlaboratory round robin study where the laboratories used a common extraction protocol and endotoxin assay kit to assay filter membranes with cotton dust containing a high and low endotoxin concentration. Again, intralaboratory variation was small and interlaboratory variation was reduced but not enough for interlaboratory agreement. But practically all of the laboratories were able to discern between the high and low endotoxin concentration dusts.

Technical Abstract: BACKGROUND: Curently there are no mandated exposure limits for endotoxin, but recommended limits have been proposed and interest expressed in developing quantitative standards for endotoxin. A limitation for developing a quantitative standard for endotoxin is the measurement variablity between laboratories. Inter-laboratory variability of up to four orders of magnitude has been reported for replicate samples. To evaluate both the intra- and inter-laboratory variability, Round-Robin studies were conducted using replicate samples of cotton dust. METHODS: Replicate samples of cotton dust were collected using vertical elutriators (VE) in a model cardroom. Each participating laboratory evaluated the samples for endotoxin using: their normal extraction procedure; a common extraction procedure; and a common extraction procedure and the same type and lot of a commercially available endotoxin kit. RESULTS: These studies demonstrated that both intra- and inter-laboratory variability is reduced by using a common extraction protocol and a common assay kit; however, significant differences remained between the laboratories. CONCLUSIONS: The data suggest that intra-laboratory assays can be used to assess the relative differences between endotoxin samples, however, the inter-laboratory variability suggests that limitations remain for developing a reliable exposure assessment assay that could be used for a quantitative exposure standard.