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Research ArticleResearch

How pH, Temperature, and Time of Incubation Affect False-Positive Responses and Uncertainty of the LAL Gel-Clot Test

Felipe Rebello Lourenço, Túlia De Souza Botelho and Terezinha De Jesus Andreoli Pinto
PDA Journal of Pharmaceutical Science and Technology November 2012, 66 (6) 542-546; DOI: https://doi.org/10.5731/pdajpst.2012.00887
Felipe Rebello Lourenço
Departamento de Farmácia, Faculdade de Ciências Farmacêuticas, Universidade de São Paulo, São Paulo, Brazil
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  • For correspondence: feliperl@usp.br
Túlia De Souza Botelho
Departamento de Farmácia, Faculdade de Ciências Farmacêuticas, Universidade de São Paulo, São Paulo, Brazil
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Terezinha De Jesus Andreoli Pinto
Departamento de Farmácia, Faculdade de Ciências Farmacêuticas, Universidade de São Paulo, São Paulo, Brazil
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Abstract

The limulus amebocyte lysate (LAL) test is the simplest and most widely used procedure for detection of endotoxin in parenteral drugs. The LAL test demands optimal pH, ionic strength, temperature, and time of incubation. Slight changes in these parameters may increase the frequency of false-positive responses and the estimated uncertainty of the LAL test. The aim of this paper is to evaluate how changes in the pH, temperature, and time of incubation affect the occurrence of false-positive responses in the LAL test. LAL tests were performed in nominal conditions (37 °C, 60 min, and pH 7) and in different conditions of temperature (36 °C and 38 °C), time of incubation (58 and 62 min), and pH (6 and 8). Slight differences in pH increase the frequency of false-positive responses 5-fold (relative risk 5.0), resulting in an estimated of uncertainty 7.6%. Temperature and time of incubation affect the LAL test less, showing relative risks of 1.5 and 1.0, respectively. Estimated uncertainties in 36 °C or 38 °C temperatures and 58 or 62 min of incubation were found to be 2.0% and 1.0%, respectively. Simultaneous differences in these parameters significantly increase the frequency of false-positive responses.

LAY ABSTRACT: The limulus amebocyte lysate (LAL) gel-clot test is a simple test for detection of endotoxin from Gram-negative bacteria. The test is based on a gel formation when a certain amount of endotoxin is present; it is a pass/fail test. The LAL test requires optimal pH, ionic strength, temperature, and time of incubation. Slight difference in these parameters may increase the frequency of false-positive responses. The aim of this paper is to evaluate how changes in the pH, temperature, and time of incubation affect the occurrence of false-positive responses in the LAL test. We find that slight differences in pH increase the frequency of false-positive responses 5-fold. Temperature and time of incubation affect the LAL test less. Simultaneous differences in these parameters significantly increase the frequency of false-positive responses.

  • Endotoxin
  • LAL test
  • Uncertainty
  • © PDA, Inc. 2012
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PDA Journal of Pharmaceutical Science and Technology: 66 (6)
PDA Journal of Pharmaceutical Science and Technology
Vol. 66, Issue 6
November/December 2012
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How pH, Temperature, and Time of Incubation Affect False-Positive Responses and Uncertainty of the LAL Gel-Clot Test
Felipe Rebello Lourenço, Túlia De Souza Botelho, Terezinha De Jesus Andreoli Pinto
PDA Journal of Pharmaceutical Science and Technology Nov 2012, 66 (6) 542-546; DOI: 10.5731/pdajpst.2012.00887

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How pH, Temperature, and Time of Incubation Affect False-Positive Responses and Uncertainty of the LAL Gel-Clot Test
Felipe Rebello Lourenço, Túlia De Souza Botelho, Terezinha De Jesus Andreoli Pinto
PDA Journal of Pharmaceutical Science and Technology Nov 2012, 66 (6) 542-546; DOI: 10.5731/pdajpst.2012.00887
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