Evaluation of a new tube latex agglutination test for detection of type-specific pneumococcal antigens in urine.

A modified tube agglutination test using type-specific latex reagents for detection of pneumococcal capsular polysaccharide antigens in alkalinized, unconcentrated urine samples was evaluated in reconstituted urine samples and in groups consisting of 26 children with clinical and roentgenographic evidence of acute lower respiratory tract infection, six patients with blood culture-proven infection of nonpneumococcal etiology, and 30 healthy individuals. The sensitivity of the tube latex agglutination method for pneumococcal polysaccharides was 2 to 10 times higher than that of the slide agglutination method. Positive antigen findings were obtained for 42% of urine samples from patients with acute lower respiratory tract infection but in neither patients with nonpneumococcal septicemia nor healthy controls. Fifty-five percent of the antigen-positive patients also showed evidence of pneumococcal involvement by pneumococcal antibody assay or antigen detection in acute-phase serum.     

Preparation of urine samples for use in commercial latex agglutination tests for bacterial antigens.

The use of latex agglutination (LA) tests for bacterial antigen detection in urine specimens is hindered by troublesome reactions such as nonspecific agglutination. Therefore, procedures such as boiling or membrane filtration of urine specimens are often used before LA testing. We discovered that the composition of the membrane filter used in filtration has a marked effect on the performance of an LA test used for detection of Haemophilus influenzae type b antigen. False-positive LA reactivity was common in urine specimens from pediatric patients that were processed by membrane filtration through certain filters; furthermore, such reactivity also occurred in LA tests for antigens other than those of H. influenzae. A protein present in urine at low concentrations appeared to be responsible for these phenomena.     

Evaluation of a commercial latex agglutination test for rapid detection of salmonella in fecal samples

A latex agglutination test for the detection of salmonella in feces was evaluated in comparison to direct culture and enriched culture using both artificially inoculated samples and clinical samples. In the samples inoculated artificially with different concentrations of salmonella (10¹ to 10⁵ per gram) the enriched culture performed better only at the 10² level in 0.4 g samples, whereas the latex test performed as well as the enriched culture at all levels in 4 g samples. In the tests using clinical samples, there was no significant difference between results of the latex test performed in 2283 samples and the enriched culture performed in 2072 samples. The sensitivity, specificity and negative and positive predictive values of the latex test were 88.2 %, 98 %, 97.5 % and 63 % respectively. The test provided results rapidly but yielded a number of false positive results.     

Noninvasive molecular diagnosis of human visceral leishmaniasis

Previously developed methods for noninvasive PCR diagnosis of visceral leishmaniasis (VL) have significant limitations. Diagnosis of VL using PCR and buccal swabs was evaluated in 307 subjects, including 148 patients confirmed to have VL. This method is simple and well tolerated and has good potential for development, showing 83% sensitivity with 90.56% specificity in control groups.     

Improvement of a direct agglutination test for field studies of visceral leishmaniasis.

To increase the potential for the wide-scale application of our direct agglutination test for visceral leishmaniasis, modifications in the components and procedures were introduced. Supplementation with 0.056 M citrate of the suspension medium stabilized the antigen for 9 weeks at 37 degrees C. To circumvent the need for cooling systems in the field, 0.2% (wt/vol) gelatin was added to the serum diluent instead of fetal bovine serum, with reliable results. Specificity and sensitivity were improved by the incorporation of 0.1 M 2-mercaptoethanol in samples with borderline titers. The test could be performed on samples of whole blood; thus the difficulties of preparation and storage of serum, plasma, or filter paper blood are avoided. For mass screening programs, a single serum dilution of 1:6,400 could be employed, contributing to a further reduction in test expenses. Sera from different geographical areas showed equal reactivities in this direct agglutination test despite the nonhomologous Leishmania donovani antigens used.     

Diagnosis of visceral leishmaniasis by enzyme-linked immunosorbent assay using urine samples

A diagnostic method has been developed to detect anti-Leishmania donovani immunoglobulin G (IgG) in urine by enzyme-linked immunosorbent assay (ELISA). In measuring anti-L. donovani IgG, IgA, and IgM in urine, the method performed best in the detection of IgG. The sensitivity and specificity of the assay were determined with panels of urine samples from 62 visceral leishmaniasis (VL) patients, 59 healthy controls from areas of endemicity, 53 healthy controls from areas of nonendemicity, 59 malaria patients, 13 tuberculosis patients, 23 cutaneous leishmaniasis patients, and 7 patients with other diseases. Using L. donovani promastigote crude antigen, the test had 93.5% sensitivity (58 positives of 62 VL patient samples) and 89.3% specificity (191 negatives of 214 non-VL patient samples). The ELISA with acetone-treated L. donovani promastigote antigen raised the sensitivity and specificity to 95.0 and 95.3%, respectively. Western blot analysis revealed that most of the samples that cross-reacted with crude antigen in ELISA did not recognize any antigenic component of L. donovani crude antigen. We also checked 40 serum samples from the same group of VL patients for anti-L. donovani IgG and got 90.0% sensitivity with both crude and acetone-treated antigens. As collection of urine is much easier than collection of serum, the detection of anti-L. donovani IgG in urine with acetone-treated antigen will be useful in epidemiological studies. It could be an adjunct of laboratory diagnosis.     

Development of a slide latex agglutination test for rotavirus antigen detection

The aim of this study was to optimize the conditions for the passive adsorption of polyclonal antibody onto plain surface polystyrene latex particles and its performance in a slide latex agglutination test for rotavirus antigen detection. Cleaning of latex particles by washing through repetitive centrifuging, decanting and resuspending in distilled water was adequate in removing surfactants from the particles' surfaces to enable coating. A study of antibody concentration, incubation temperature and buffer pH revealed that optimum coating was achieved with a 3-fold excess of antibody to the calculated total particle surface capacity for the antibody in a glycine-saline buffer of pH 9.2 at 40 degrees C for 4 hours. The ionic strength and pH of the latex suspending buffer and the sample buffer were critical factors determining the sensitivity of the test and the appearance of non-specific agglutination. Ultrasonication, addition of glycerol and Tween 20, either individually or in combination, were able to suppress non-specific agglutination in some batches of latex reagents. Polyethylene glycol 6000 enhanced the quality of agglutination as well as reduced the time of its appearance, especially in reagents that produced poor agglutination.     

Rapid diagnosis of rotavirus gastroenteritis by a commercial latex agglutination test.

The Rotalex test, a commercial latex agglutination test for rotavirus, was compared with direct electron microscopy (EM) and the Rotazyme test I, a commercial enzyme immunoassay, for detection of rotavirus in stools of children and neonates. For initial stool specimens from 265 children (less than 3 years old) with diarrhea, the Rotalex test had a sensitivity of 81.7% and specificity of 99.5% compared with EM results. Positive and negative predictive values were 98 and 94.9%, respectively. The Rotalex test was slightly more sensitive and specific than the Rotazyme test. When daily stool specimens from patients with rotavirus gastroenteritis were examined, the sensitivity of the Rotalex test varied depending on the time of stool collection relative to the onset of symptoms. Sensitivity was 100 (20/20), 96 (23/24), and 54% (7/13) during 1 to 4, 5 to 7, and 8 to 18 days, respectively, after the onset of symptoms. The sensitivity of the Rotazyme test varied similarly with days from onset. We also examined 214 EM-negative stool specimens from asymptomatic newborns. False positivity by the Rotalex test was only 3.3% (7/214) compared with 4.2% (9/215) for the Rotazyme test. The Rotalex test was as sensitive and specific as EM for detection of rotavirus during the acute stage of illness and much faster and cheaper than EM or the Rotazyme test. The test appears to be suitable for routine use in small hospitals, emergency wards, or even the physician's office for rapid diagnosis of rotavirus gastroenteritis.     

Evaluation of a latex agglutination test for diagnosis of Clostridium difficile-associated colitis

Current methods for diagnosis of Clostridium difficile-associated colitis (CAC) based on detection of cytotoxin B by a tissue culture assay (TCA) require technical expertise and up to 48 hours incubation. Recently, a latex agglutination (LA) test (Marion Laboratories) for rapid diagnosis of CAC has become available. Although early evaluations have been favorable, new evidence suggests that the LA reagent binds a soluble bacterial antigen that is not unique to toxigenic strains of C. difficile. The authors examined 201 stools received for CAC testing by LA and a reference TCA and investigated discrepant results. They obtained 29 LA(+)/TCA(+) and 155 LA(-)/TCA(-) results. Eleven patients had LA(+)/TCA(+) and 155 LA(-)/TCA(-) results. Eleven patients had LA(+)/TCA(-) results and 6 had LA(-)/TCA(+) results. The sensitivity and specificity of the LA were 83% and 93%, respectively, compared with TCA. The predictive values of positive and negative results obtained with the LA were 72% and 96%, respectively. Concentrated broth supernatants and live suspensions of three C. difficile isolates with LA(+)/TCA(-) results were tested in a rabbit ileal loop assay. All failed to demonstrate ability to produce an enterotoxin. The authors conclude that the LA method is suitable for rapid screening, but LA(+) results require confirmation by testing with other methods.     

Modified direct agglutination test for simplified serologic diagnosis of leishmaniasis

Human leishmaniasis is a severe health problem in many countries around the world. Hence, a cheap, reliable, and accurate diagnostic test is required to fight this disease. Perhaps the direct agglutination test (DAT) meets these criteria, but antigen elaboration involves many difficulties. We have developed a new antigen elaboration method, the EasyDAT method, that avoids the problems associated with the DAT. In this study, we compared the traditional DAT antigen method with our EasyDAT antigen method by using canine sera. The sensitivities (100%) and specificities (98.7%) were the same for both methods; we therefore concluded that the EasyDAT Leishmania antigen method simplifies serologic diagnosis, making this method easier and cheaper to use.     

Evaluation of cleaving agents other than trypsin in direct agglutination test for further improving diagnosis of visceral leishmaniasis.

Trypsin treatment of Leishmania promastigote antigen has proved to be indispensible in the direct agglutination test (DAT) for the diagnosis of visceral leishmaniasis (VL) and canine visceral leishmaniasis (CVL). In the present study four antigen batches were prepared with pronase (400 micrograms/ml), lipase (0.45% [wt/vol]), pancreatin (0.3% [wt/vol]), or 2-mercaptoethanol (2-ME) (1.2% [vol/vol]) at a ratio of 20:1 versus promastigote packed cell volume or a density of 10(8)/ml. Batches prepared in this way performed satisfactorily when compared with the performance of the initial trypsinated antigen. Even higher was the sensitivity and specificity of the 2-ME-processed antigen, scoring a minimum DAT titer of 1:102,400 in the VL and CVL group and a maximum of 1:400 in the negative control group. Corresponding titers ranging from 1:6,400 to 1:12,800 and 1:800 to 1:1,600 were obtained with the antigen variants processed with pronase, lipase, pancreatin, or trypsin. By combining the use of indigenous Leishmania donovani subspecies from Sudan, Bangladesh, or Morocco and incorporating 2-ME instead of trypsin in the antigen processing step, a threefold increase in titer was attained in sera from the respective areas where VL is endemic. 2-ME-processed antigen suspensions maintained stability at 4 degrees C for up to 9 months, as evidenced by the absence of autoagglutination and the reproducibility of DAT readings with standard sera. The specificity of DAT was further improved by supplementation of the sample diluent with 0.03 M urea and incubation of the test plates at 37 degrees C for 1 h.(ABSTRACT TRUNCATED AT 250 WORDS)     

Avidin-biotin latex agglutination assay for detection of antibodies to viral antigens.

A new method for attaching antigens to latex by an avidin-biotin technique is described. The procedure permits control of the amount of antigen attached to the latex and eliminates the need for highly purified antigens and destructive bridging chemicals. The avidin-biotin latex agglutination assay is a simple, rapid test well suited to detection of viral antibody. The sensitivity and specificity, respectively, of the avidin-biotin latex agglutination assay compared with other assay results for antibody to viruses were as follows: cytomegalovirus, 98 and 100% (indirect hemagglutination assay); measles virus, 96 and 100% (enzyme-linked immunosorbent assay); and herpes simplex virus, 78 and 100% (indirect hemagglutination assay).     

Evaluation of a new slide latex agglutination test for diagnosis of vaginal candidosis

A new commercial slide latex particle agglutination test for rapid (2 min) diagnosis of vaginal candidosis was evaluated and compared with conventional methods. Of the 263 women studied, 63 (23.9%) had yeasts in the vagina. Clinical signs of vulvitis or vaginitis were seen in 23 women (8.8%) and 40(15.2%) were harbouring yeasts without clinical signs. Yeast counts were generally higher in women with clinical signs of vaginal candidosis than in those without. The test was positive in 15 of the 23 women (65.2%) with clinical signs, the incidence of a positive test increasing in direct proportion to the amount of yeasts isolated. The test's sensitivity, specificity and predictive values were comparable to those of microscopy and culture. Being both rapid and simple to perform, this new test offers a useful alternative to conventional methods for the diagnosis of vaginal candidosis.     

Rapid diagnosis of Clostridium difficile-associated diarrhoea using a latex agglutination test

A rapid latex agglutination test, Culturette Brand CDT from Marion Laboratories, was evaluated and compared to a tissue culture assay (TCA) and isolation of Clostridium difficile in 380 faecal specimens from 226 patients with clinically suspected Clostridium difficile-associated diarrhoea. The sensitivity and specificity of the latex test compared with the TCA were 83% and 80% respectively, and the positive and negative predictive values were 55% and 94% respectively. In patients with repeated sampling the sensitivity increased to 95%. The latex test may be useful as a screening test for negative specimens in laboratories where TCA is not available, but positive specimens have to be confirmed by TCA.     

A latex slide agglutination test for rapid detection of antimyeloperoxidase antibody

AIM: To develop and test a new latex slide agglutination test (MPO-LSAT) to detect antimyeloperoxidase (anti-MPO) antibody in serum. METHODS: Latex bead coating was adjusted to give maximum sensitivity by attending to latex size, MPO to latex ratio for coupling, ratio of diluted serum to MPO-latex, reaction time and temperature for coupling, and reaction time for agglutination. Inhibition studies were performed using MPO, proteinase 3, bactericidal/permeability increasing protein, and lactoferrin. RESULTS: There was very good correlation between this test and the conventional anti-MPO enzyme linked immunosorbent assay (ELISA): 81% of sera positive in the ELISA were positive by MPO-LSAT. MPO-LSAT results correlated better with IgM anti-MPO than with IgG anti-MPO. CONCLUSIONS: MPO-LSAT is a simple diagnostic test that is potentially useful in the clinical laboratory as a rapid screening tool for vasculitic diseases.     

Commercial latex agglutination test for detection of Clostridium difficile-associated diarrhea.

A commercially available latex agglutination test for Clostridium difficile was compared with a cell culture cytotoxin assay and bacteriological culture for the laboratory diagnosis of C. difficile-associated diarrhea and colitis (CAD). Stool specimens from 626 patients were tested by the three methods, and specimens from 118 patients (19%) were positive by at least one of the methods. The results of the three tests agreed in 88% of the specimens tested, overall, but they agreed in only 34% of the 118 positive specimens. Ninety-three patients were evaluated to assess the significance of positive and negative results for each assay. Of 40 patients found to have CAD, 70% were positive by the cytotoxin assay, 78% were positive by the latex agglutination test, and 90% were culture positive. Of 53 patients who did not have CAD, 2% were positive by the cytotoxin assay, 8% were positive by the latex test, and 4% were culture positive. The detection of CAD was improved by using the tests in combination, and 97% of specimens positive by two or three methods were from patients who had CAD. Testing of multiple specimens from individual patients also increased the sensitivity of detection of CAD. The results suggest that the latex agglutination test may be useful for rapid diagnosis of CAD, especially in laboratories that lack cell culture facilities. However, the accuracy of CAD detection is improved when the latex test is used in combination with culture or the cytotoxin assay.     

Evaluation of a new latex agglutination test for detection of streptolysin O antibodies.

Acute- and convalescent-phase serum specimens were collected from 50 patients with group A streptococcal pharyngitis. The anti-streptolysin O (ASO) titer for each serum specimen was determined by using both the standard neutralization assay and the latex agglutination (LA) test (Rheumagen ASO; Biokit Inc., New Britain, Conn.). When the ASO titers derived by the two methods were compared, the correlation coefficient was 0.93. When the ability of the LA test to demonstrate a significant ASO titer rise (greater than or equal to 2 dilutions) was compared with that of the standard neutralization assay, the LA test had a sensitivity of 91%, a specificity of 86%, a positive predictive value of 83%, and a negative predictive value of 92%. Triplicate LA test determinations were performed on a subset of 31 serum specimens, and for 29 (94%), the repeated ASO titers were all within 1 dilution of each other; the width of the 95% confidence interval for the triplicate measurements of each serum specimen was +/- 32.8 IU. We found the Rheumagen ASO to be a simple, rapid LA procedure for measuring ASO titers that produces results that are highly reproducible, show little lot-to-lot variability, and are comparable to the ASO titers obtained with the standard neutralization assay.     

Retrospective evaluation of a latex agglutination test for diagnosis of invasive aspergillosis in immunocompromised patients

A commercial latex agglutination (LA) test for the detection of circulatingAspergillus galactomannan was evaluated in sera obtained from 121 immunocompromised patients, including 19 with proven invasive pulmonary aspergillosis. Patient urine (the specimen of choice for detection of galactomannan) was not tested with the LA test as 34 of 81 specimens from controls gave false-positive results. The sensitivity (95 %), specificity (90 %) and negative predictive value (99 %) of the LA test were similar to previously published results obtained with two EIAs. However, the positive predictive value was only 67 % compared to 95 % obtained with the EIAs. In addition, the LA test was also of less value than the EIAs in predicting the onset of invasive pulmonary aspergillosis. It was the earliest indicator of infection in only 1 of 19 proven cases.     

Evaluation of the latex agglutination test for detection of Clostridium difficile.

We compared two Clostridium difficile latex agglutination tests, Meritec from Meridian Diagnostic (Cincinnati, Ohio) and CDT from Becton-Dickinson (Cockeysville, Md), on 289 specimens submitted for tissue culture cytotoxicity using MRC-5 cells. When compared with CDT, the Meritec latex agglutination test had a sensitivity of 90% (26/29), a specificity of 97% (251/260), and a correlation of 96%. Meritec was compared with tissue culture cytotoxicity on 357 specimens. Meritec had a sensitivity of 77% (30/39), a specificity of 93% (298/318), and a correlation of 92%. Clinical review of 10 Meritec +/- tissue culture cytotoxicity minus patients revealed one likely, two probable, and seven doubtful cases of C difficile disease. In contrast, review of 10 Meritec +/- tissue culture cytotoxicity plus patients showed seven likely and three probable cases of C difficile disease. The Meritec is comparable with the CDT latex agglutination test, but is not nearly as sensitive as either tissue culture assay or culture for detection of C difficile disease. A positive latex agglutination test should be confirmed by a tissue culture cytotoxicity assay.