Application of a Limulus test device in rapid evaluation of gonococcal and nongonococcal urethritis in males

Abstract

A test device incorporating Limulus amoebocyte lysate (Mallinckrodt, Inc., St. Louis, Mo.) was developed for the rapid, presumptive diagnosis of gonococcal and nongonococcal disease in males. The device, which was evaluated in 550 men with exudative urethritis, consisted of a specimen collection syringe, a dilution reservoir containing 10 ml of pyrogen-free water, and a Limulus amoebocyte lysate singletest vial. After specimen collection, the syringe was affixed to the dilution reservoir for rapid, accurate dilution of the clinical sample. Contamination of the specimen and potential biohazards to the user were prevented. The diluted sample was then transferred (via the collection syringe) to the lysate test vial for assay of endotoxin. Various incubation times at 37°C were also studied in an additional 301 male patients, and time was reduced from the standard 60 to 30 min while still retaining equivalent predictability of culture results (P > 0.05). Of the 550 males evaluated with the test device, 366 had positive cultures for Neisseria gonorrhoeae, and 184 were negative. A sensitivity of 99.2% and a specificity of 96.7% were obtained with the test device. Overall ability to predict culture results was 98.4%. Gram-stain sensitivity and specificity were 96.4% and 99.5%, respectively, with an overall accuracy of 97.5%. There were no statistical differences between the Limulus amoebocyte lysate test and Gram stain in predicting cultures (P > 0.05). Thus, use of the Limulus amoebocyte lysate test device would enable the private physician to make an accurate, presumptive diagnosis of gonococcal and nongonococcal disease in males with exudative urethritis within 30 min without the need of a microscope and to initiate proper therapy during the patient's initial evaluation.

Improved utility of Gonoscreen, a Limulus amoebocyte lysate assay, in the evaluation of urethral discharges in men

“…The sample collection utilized in the Gonoscreen test involves the use of a needleless tuberculin syringe to gently aspirate the discharge. While this method is effective in obtaining urethral samples, at least 15 pl of discharge is required to obtain accurate results (13).…”

“…In these studies, sensitivities and specificities ranged from 95 to 100%o and 89 to 100%o, respectively, and overall accuracies to predict culture results were 94 to 1001%. Unlike Gram stains, which require experienced microscopists to read many smears a week to obtain highly accurate results (3), the LAL assay can provide similar results and can be performed by those unskilled in laboratory procedures (13). Consequently, an LAL test kit (Gonoscreen; Mallinckrodt, Inc., St. Louis, Mo.)…”

Lack of utility of a Limulus amoebocyte lysate assay in the diagnosis of urethral discharges in men

“…The relative abundance of endotoxin in the outer membrane of Neisseria gonorrhoeae (4) has also been used to distinguish gonococcal (GCU) from nongonococcal urethritis (NGU). Previous studies have demonstrated that the diagnostic accuracy of LALA in urethral exudates is equivalent to a Gram-stained smear (10)(11)(12)(13)15).…”

Evaluation of Gonodecten for the presumptive diagnosis of gonococcal urethritis in men

“…A commercially available enzyme immunoassay test has been demonstrated to be useful for the detection of Neisseria gonorrhoeae in both male urethral and female endocervical specimens (2, 12). The Limulus amoebocyte lysate test, which detects gonococcal lipopolysaccharide, has also been evaluated for screening and diagnosing gonorrhea in male and female genital specimens (10,11). When tested with male urethral exudates, the Limulus assay was 99.2% sensitive and 96.7% specific for the detection of N. gonorrhoeae when compared with the Gram stain (10).…”