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Limulus amebocyte lysate test for endotoxemia: investigations with a femtogram sensitive spectrophotometric assay
Abstract:
The question of specificity of Limulus amebocyte lysate (LAL) test in the diagnosis of endotoxemia has been a limiting factor of its clinical application. Using a femtogram-sensitive spectrophotometric LAL assay 35 of 36 septic postoperative patients showed an excellent correlation (almost 100%) between positive LAL tests and culture-proven gram-negative bacteremia. Twenty patients of this group demonstrated a significant correlation (p < 0.05) between elevated total white blood cell counts and Escherichia coli Endotoxin equivalents (EcEe). All 22 liver cirrhotic patients with potentially enteric endotoxemia yielded LAL positive reactions (100%) but 9 of 22 correlated significantly as to leucocytosis and elevated EcEe (2 p < 0.01). A significant correlation between EcEe and leucocyte counts was found for all neonates and all parturients respectively (2 p < 0.001), 2 p < 0.01). In vitro tests showed that leucocytes gave positive LAL tests. Supernates of a Ficoll sedimented crude leucocyte preparations, induced LAL positivity in a dose dependent manner, while all reagents per se used in the preparation, were negative. This study suggests that heat-labile factors from leucocytes apart from endotoxin are responsible for positive LAL reactions.
Insights
The Limulus amebocyte lysate (LAL) test shows high correlation with gram-negative bacteremia in septic patients. Leukocytes, not just endotoxins, may cause positive LAL test results in clinical settings.
Area of Science:
- Clinical Microbiology
- Immunology
- Biochemistry
Background:
- The clinical utility of the Limulus amebocyte lysate (LAL) test for diagnosing endotoxemia is limited by concerns regarding its specificity.
- Endotoxemia diagnosis is crucial for effective patient management in critical care settings.
Purpose of the Study:
- To investigate the specificity of the LAL test in various clinical conditions.
- To determine the correlation between LAL test results, endotoxin levels, and white blood cell counts.
- To explore the role of leukocytes in positive LAL reactions.
Main Methods:
- A femtogram-sensitive spectrophotometric LAL assay was employed.
- Patient cohorts included septic postoperative patients, liver cirrhotic patients, neonates, and parturients.
- In vitro experiments assessed LAL reactivity of leukocyte preparations.
Main Results:
- A near 100% correlation was observed between positive LAL tests and gram-negative bacteremia in 35 of 36 septic patients.
- Significant correlations were found between elevated white blood cell counts and Escherichia coli Endotoxin equivalents (EcEe) in septic patients, liver cirrhotic patients, neonates, and parturients.
- In vitro studies demonstrated that leukocytes induce dose-dependent LAL positivity, suggesting heat-labile factors from leukocytes contribute to the reaction.
Conclusions:
- The LAL test demonstrates high sensitivity for detecting gram-negative bacteremia.
- Leukocytes, through heat-labile factors, appear to contribute to positive LAL test results, potentially impacting specificity.
- Further research is needed to elucidate the precise mechanisms and clinical implications of leukocyte-derived factors in LAL reactivity.