Response of several Limulus amoebocyte lysates to native endotoxin present in gonococcal and nongonococcal urethral exudates from human males

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Abstract
Three Limulus amoebocyte lysate (LAL) preparations obtained from 3 different suppliers were comparatively evaluated for sensitivity to native endotoxin contained in urethral exudates from 28 men with gonococcal urethritis and 16 men with nongonococcal urethritis. One LAL preparation was not extracted with organic solvents during manufacture; the other 2 were extracted with chloroform. All 3 LAL preparations had equivalent sensitivities (0.06 ng/ml) to an established reference endotoxin standard (EC-2), but significant differences in sensitivities were found among the different LAL preparations when testing clinical specimens. Dilution breakpoints of urethral samples for maximum sensitivity and specificity ranged from 1:400-1:1600, depending on the LAL preparation. The nonextracted lysate was significantly more sensitive to the presence of endotoxin in gonococcal exudates than the other 2 preparations (P < 0.001) but not significantly different from 1 LAL preparation (P > 0.05) in detecting endotoxin in nongonococcal exudates. An additional 116 men, 61 with culture-proven gonococcal urethritis and 55 with nongonococcal urethritis, were evaluated with 3 lots of nonextracted lysate with sensitivities ranging from 0.04-0.06 ng/ml, reference endotoxin EC-2. At a dilution breakpoint of 1:1600, the sensitivity of the LAL test was 100%; the specificity was 96%.