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PubMed1998

False-positive coliform reaction mediated by Aeromonas in the Colilert defined substrate technology system.

The Colilert defined substrate technology system allows specific, one-step detection of both coliforms and Escherichia coli while claiming to suppress the influence of non-coliform heterotrophs. The Colilert assay was examined in order to determine whether organisms from the genus Aeromonas could interfere and cause production of a false-positive coliform result as aquatic Aeromonas are known to constitute a fraction of the heterotrophic population found in drinking water. Results obtained clearly demonstrate that Aeromonas sp. can elicit a positive coliform type reaction at very low densities. Cell suspensions as low as 1 x 10(1) cells 10 ml-1 were observed to yield a positive reaction using Colilert reagent 4 weeks short of shelf-life expiry. Use of aged Colilert for monitoring water quality could lead to overestimation of coliforms as Aeromonas have been identified in many treated drinking water supplies.

Aeromonas↗
PubMed1976

Lupus erythematosus and reactive tests for syphilis: update.

Sera of patients with lupus erythematosus can produce false-positive reactions in most serologic tests for syphilis, including the FTA-ABS test. False-positive reactions in the FTA-ABS test can exhibit beaded, borderline or reactive patterns of fluorescence. Beaded fluorescence is commonly associated with anti-DNA antibody and other correlates of lupus activity. Borderline and reactive results are common in both systemic and discoid lupus erythematosus, and are usually not associated with increased clinical activity. TPI and MHA-TP tests appear helpful in detecting false-positive FTA-ABS results.

False Positive Reactions↗
PubMed1979

The frequency and identification of false positive conversion reactions.

The frequency with which conversion reaction diagnoses are inappropriately applied to persons with physical diseases was estimated in a sample of medical hospital patients diagnosed hysteric. This was accomplished by ratings based on file information available at the time of diagnosis and at a 10-year follow"up, and a count of patients whose "conversion" symptoms were later diagnosed as physical illnesses. The estimated false positive rate was 25%. The symptoms most characteristic of the false positives were degenerative diseases and structural failures affecting the spinal cord, peripheral nerves, bones, muscles, and connective tissues. An effort to identify psychological parameters capable of separating true conversion reactions from false positives with a variety of behavioral symptoms and Minnesota Multiphasic Personality Inventory scores was not productive.

Conversion Disorder↗
PubMed1974

Specificity and sensitivity of radioimmunoassay for hepatitis B antigen.

Sera from a survey of 6,026 people were tested for hepatitis B surface antigen by using radioimmunoassay and counterelectrophoresis. Forty-eight sera (0.79%) were positive by counterelectrophoresis and 152 sera (2.52%) were positive by radioimmunoassay, using the most liberal of the recommended criteria for positivity (i.e., counts 3 standard deviations above the mean). Absorption tests performed on the 152 radioimmunoassay-positive sera showed that 10 (6.6%) were false-positive reactions to guinea pig protein, 74 (48.6%) were due to false-positive reaction(s) with other protein(s) in the test system, and 68 (44.8%) were true positives. There was a strong correlation between the degree of elevation of radioactive counts and the proportions of sera that were true positives; all 49 sera with counts >50 standard deviation units above the mean were true positives, but only 19 (18.4%) of the 103 sera with counts <50 standard deviation units were true positives. A few sera with high counts required absorption with type-specific (type D) antisera. The following conclusions were reached from this study: (i) absorption tests should be run on all radioimmunoassay-positive, counterelectrophoresis-negative sera; (ii) most (about 90%) false positives are not due to anti-guinea-pig protein reactions; and (iii) radioimmunoassay, in combination with absorption tests, yields a modest increase (about 35%) in detection of true positives over use of counterelectrophoresis alone.

Animals↗
PubMed1996

Cholera-Brucella Cross-Reaction: A New Potential Diagnostic Problem for Travelers to Latin America.

Background: Brucellosis is an endemic disease in Latin America and other countries. Serologic cross-reaction between cholera and Brucella infection is well recognized. Since the introduction to cholera in 1991 in Latin America, interpreting serologic tests has become potentially problematic. This study attempts to evaluate this problem. Methods: Tube agglutination tests were performed to detect Brucella antibodies in 44 Peruvian adult patients with moderate to severe diarrhea due to Vibrio cholerae O1 El Tor infection. These patients had no prior history and no clinical evidence of brucellosis. Results: False positive reactions were observed in 43.2% and 15.9% of the patients when cut-off points of >= 1/80 and >= 1/160 titer, respectively, were selected. These false positive reactions occurred within 4 to 14 days after the onset of diarrhea. The cross-reactivity decreased at the end of the fifth week (only 8.33% had a positive value at the fifth week). Conclusions: Physicians should be alert to the false positive reaction to Brucella in patients with diarrhea. This is relevant to the evaluation of febrile illness in patients coming from developing countries where they could have been exposed to cholera.

Journal Article↗
PubMed2004

Cross-reaction of SARS-CoV antigen with autoantibodies in autoimmune diseases.

To investigate the significance of the SARS-associated coronavirus (SARS-CoV) antibody, detected by ELISA and indirect immunofluorescence assays (IFA) for the SARS-CoV Vero E6 cell lysates, in non-SARS subjects, 114 serum samples from healthy controls and 104 serum specimens from autoimmune disease patients were collected. The results of ELISA showed that among 114 sera from healthy controls, 4 (3.5%) were positive of SARS-CoV-IgG antibody and 114 (100%) were all negative of SARS-CoV-IgM antibody; the specificity of SARS-CoV-IgG antibody for SARS patients was 96.5%, but the specificity of both SARS-CoV-IgG and -IgM antibodies for SARS patients was 100%. In 58 cases with SLE, positive rates of SARS-CoV-IgG and -IgM antibodies were 32.8% (19/58) and 8.6% (5/58), respectively, in which 11 cases (19%) were positive of both SARS-CoV-IgG and -IgM antibodies; in 10 cases with SS, positive rate of both SARS-CoV-IgG and -IgM antibodies was 10% (1/10); in 16 cases with MCTD, positive rate of SARS-CoV-IgG was 37.5% (6/16), positive rate of both SARS-CoV-IgG and -IgM antibodies was 6.3% (1/16); in 20 cases with RA, one case was positive (5%) of SARS-CoV-IgG. However, of all samples with positive SARS-CoV-IgG and -IgM antibodies for autoimmune diseases and healthy controls, SARS-CoV RNA and antibodies were all negative by RT-PCR and IFA. All sera for negative or positive ELISA results were also negative or positive results using ELISA with Vero E6 cells lysates. These studies showed that SARS-CoV Vero E6 cell lysates for the ELISA to detect SARS-CoV antibodies could lead to the false-positive reactions or cross-reactions of SARS-CoV antibodies in non-SARS diseases and healthy controls, and the false-positive reactions or cross-reactions were related to Vero E6 cell lysates and autoantibodies in non-SARS population.

Animals↗
PubMed1982

Histochemical diagnosis of Hirschsprung disease.

A histochemical staining technique for detection of acetylcholinesterase (AChE) in rectal suction biopsies was compared with the presence or absence of ganglion cells in full-thickness or suction biopsies for the diagnosis of Hirschsprung disease (HD) in infants and children. Biopsies from 55 of 58 children were adequate for both the AChE assay and routine pathologic examination for ganglion cells. Two patterns of AChE staining were noted. With pattern A, prominent nerve fibers staining for AChE were seen throughout the muscularis mucosa and the lamina propria. With pattern B, similar fibers were seen only in the muscularis mucosa and the areas of lamina propria that were immediately adjacent. No "false-negative" AChE staining reactions were found in patients with HD. No "false-positive" reactions showing pattern A were found. This pattern was diagnostic for HD. Three false-positive reactions were found showing pattern B in patients with conditions other than HD. Among 22 patients with HD, 19 were males and three were females. Pattern A occurred in all age groups and in both sexes. Pattern B in patients with HD was seen exclusively in male infants 1 month of age or less. Experience suggests that the AChE staining of rectal suction biopsies is an excellent screening test for HD in infants and children. If pattern B is encountered, however, the specimen should be examined by routine pathologic techniques for the presence of submucosal ganglion cells.

Acetylcholinesterase↗
PubMed1991

Competition ELISA using a human monoclonal antibody for detection of antibodies against human immunodeficiency virus type 1.

A novel competition ELISA for detection of antibodies against HIV-1 was developed. The assay is based on competition at the single epitope level and utilises a human monoclonal antibody and an E. coli-produced fragment of the transmembrane glycoprotein gp41. The sensitivity of the assay was 100% in tests on 247 serum samples obtained from 219 individuals previously shown to be HIV-1 antibody positive by both conventional indirect ELISA and the immunoblotting test. The patients represented various clinical and immunological stages of HIV-1 infection. Likewise, the specificity of the assay was 100% in tests on 105 serum samples from normal individuals previously tested negative by indirect ELISA. Further, among 105 serum samples selected due to consistent false positive reactions in the indirect ELISA only 2 samples (1.9%) demonstrated false positive reactions in the competition ELISA, i.e. 98.1% specificity. Finally, only 2 of 57 (3.5%) serum samples from HIV-2 infected individuals showed positive reactions in the assay, while 54 (94.7%) had absorbance values similar to the negative controls. These results demonstrate that human monoclonal antibodies may form the basis for highly sensitive and specific assays for detection of antibodies to HIV-1.

AIDS Serodiagnosis↗
PubMedDate not supplied

[The "false-positive" patch test reaction].

If a positive patch test reaction occurs in the absence of sensitization to a certain antigen, we call it a false positive reaction. There may be several reasons for this: impurities of the test substances, too high a concentration, wrong choice of test location and reading time; positive reactions against test vehicle, or adhesive tape, nonspecific reactions due to adjacent strongly positive patch test reactions and finally wrong interpretation by the doctor. Diagnosis of contact allergy, especially to potent allergens or topical medications and questions relating to occupational disease may be of eminent importance to the patient. Therefore false positive as well as false negative test reactions should be recognized; this also appears particularly important for medicolegal reasons.

Dermatitis, Contact↗
PubMed1997

Influence of postmortem changes on immunohistochemical reactions in skin.

The influence of postmortem damage of tissues on the immunohistochemical diagnosis of wound age has not as yet been clarified. We utilized antibodies against the proteinase inhibitors alpha-1-antichymotrypsin and alpha-2-macroglobulin, fibronectin and lysozyme to study samples of skin which had been intact intravitally, but were damaged postmortem either by autolysis or compression with a surgical clamp at the time of dissection. Even in the absence of autolysis, antibodies against the proteinase inhibitors and fibronectin exhibited staining of tissue margins. Autolysis caused an increase in false positive results. In contrast, antibodies against lysozyme did not give false positive staining. There were no antigens sensitive to postmortem clamping and false positive results were not observed. Antibodies against proteinase inhibitors are not useful for the diagnosis of wound age because of a high number of false positive reactions in marginal areas. Fibronectin also showed false positive band-shaped staining patterns at the tissue margin. In addition, autolytic processes increase the number of false positives. The antibody against lysozyme is much less sensitive to autolysis and no false positive reactions were observed in our series of tests.

Fibronectins↗
PubMed1976

Late syphilis. Otologic symptoms and results of the FTA-ABS test.

The clinician occasionally encounters a patient whose cochleovestibular symptoms are thought to be due to late syphilis mainly on the basis of a reactive FTA-ABS test. I describe 21 such patients, 11 of whom had either a spurious- or a false-positive reaction. The following suggestions may avoid an inaccurate diagnosis of late syphilis in such patients: (1) repeat all reactive serological tests for syphilis (STS); (2) rule out false-positive reactions; (3) request the degree of fluorescence (1+ to 4+) on all reactive FTA-ABS tests; (4) obtain a Treponema pallidum immobilization (TPI) test on all patients with repeatedly reactive (1+) FTA-ABS tests--a nonreactive TPI test rules out the diagnosis of syphilis; (5) if a TPI test cannot be performed, a repeatedly reactive (1+) FTA-ABS test in the absence of a reactive nontreponemal STS probably represents a false-positive reaction; (6) clinical judgment is the final determinant of whether a patient has or should be treated for late syphilis.

Adult↗
PubMed1991

Isolation and purification of a diagnostic antigen for bovine cysticercosis by hydrophobic chromatography.

An ammonium sulfate fraction of Taenia hydatigena cyst fluid (ThFAS) was further fractionated by hydrophobic interaction chromatography, using alkylagarose and omega-amino alkylagarose columns, in an effort to isolate and purify a specific diagnostic antigen in the ThFAS preparation. The less than 12 kDa antigen was found to have an affinity for immobilized alkanes with chain length of six carbons or greater. The antigen was recovered in an ethylene glycol eluate from a hexylagarose column then analyzed by Western blot; it reacted with bovine and human cysticercosis infection sera and with specific monoclonal antibodies but not with control sera or fascioliasis infection sera. When the eluate was used as coating antigen in a plate ELISA assay no false positive reactions were seen in sera from cattle infected with Fasciola hepatica; false positive reactions were observed for the unfractionated ThFAS antigen preparation.

Animals↗
PubMed1987

Evaluation of the multitest medium for rapid presumptive identification of Vibrio cholerae from environmental sources.

The multitest V. cholerae medium (VC medium) for rapid presumptive identification of Vibrio cholerae was evaluated. On the basis of reactions in the VC medium, 379 strains recovered during a yearlong ecological study in Calcutta were presumptively identified as V. cholerae. Further phenotypic characterization of these strains revealed that the reactions of 371 (97.9%) isolates were consistent with that of V. cholerae. False-positive reactions were exhibited by eight (2.1%) strains, three of which were identified as Vibrio fluvialis biotype 1. By slightly varying the basic formulation of the VC medium, we could eliminate some false-positive reactions. On the basis of the present evaluation, we recommend the routine use of the VC medium.

Culture Media↗
PubMed1989

Diagnosis of human hydatid disease in surgically-confirmed cases by the use of the indirect haemagglutination test based on a thermo-stable lipoprotein and on unfractionated hydatid cyst fluid.

A total of 204 sera, taken from healthy individuals or from individuals with various parasitic and bacterial infections, were examined by the indirect haemagglutination test. The tests were carried out using either a thermo-stable lipoprotein or unfractionated hydatid cyst fluid, and a titre of 1:64 or above was considered positive. Sixty-two of 70 sera from individuals with surgically-confirmed hydatid disease showed positive reactions with the thermo-stable lipoprotein--a sensitivity of 88%. No false positive reactions were obtained with sera from healthy individuals or from individuals with parasitic or bacterial infections, and no cross-reactions were observed with sera from individuals with multiple myeloma. The lipoprotein antigen thus showed a specificity of 100%. A sensitivity of 88% was obtained with the indirect haemagglutination test using whole hydatid cyst fluid; but positive reactions were obtained from healthy individuals and from individuals with schistosomiasis, leishmaniasis, taeniasis and malaria. No cross-reactions were obtained with sera from patients with gonorrhoea, syphilis or multiple myeloma. Because of the high sensitivity and specificity shown by the thermo-stable lipoprotein ('Antigen 880'), it is considered that this antigen is more useful than unfractionated hydatid cyst fluid in the diagnosis of human hydatidosis in Kenya.

Animals↗