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PubMed1973

The Treponema pallidum haemagglutination (TPHA) test in biological false positive and leprosy sera.

The Treponema pallidum haemagglutination (TPHA) test was carried out on 274 sera known to show biological false positive reactions to reagin tests for syphilis. The Treponema pallidum immunization (TPI) and fluorescent treponemal antibody absorption (FTA-ABS) tests were non-reactive on all these sera. Thirty-one or 11.3% showed reactive results in the TPHA test. Sera from 267 people who had lepromatous leprosy were also tested in the TPHA test. Fourteen sera were reactive in the TPHA, TPI, and FTA-ABS tests and were from people who had both syphilis and leprosy. Biological false positive reactions were shown by 26 of the leprosy sera, of which three or 11.5% were also reactive in the TPHA test. A further four sera in the leprosy group were reactive only in the TPHA test. The possible cause of false reactive TPHA test results is discussed. It was concluded that where reagin and TPHA tests are reactive in a person who has no history or clinical signs of syphilis, the serum should be referred for TPI and FTA-ABS testing.

Antibodies, Bacterial↗
PubMedDate not supplied

Evaluation of TDx cocaine metabolite assay.

The TDx cocaine metabolite fluorescence polarization immunoassay (Abbott Laboratories) for the detection of benzoylecgonine (BE) in urine was evaluated. The threshold concentration for BE detection was 0.3 mg/L. The within- and between-run precision of the assay gave coefficients of variation less than 2.3% and 3.5%, respectively. One hundred twenty clinic urines positive for BE by high-pressure liquid chromatography (HPLC) were analyzed by the TDx and EMIT-dau cocaine metabolite assays. All three methods were positive for BE in 116 samples, 96.7%. Two samples were positive by TDx and negative by EMIT-dau, and two samples were positive by EMIT-dau and negative by TDx. Cocaine and ecgonine methyl ester cross reactivity with the TDx assay was less than 2%. One hundred drugs and drug metabolites were added to drug-free urine resulting in no false positive reactions. The same drugs and drug metabolites were also added to urine with 3.0 mg/L BE and analyzed by the TDx. No false positive reactions or inhibition of BE detection occurred.

Cocaine↗
PubMed1986

Comparative evaluation of identification systems for testing methicillin-resistant strains of Staphylococcus aureus.

Several commercial systems are available to distinguish between Staphylococcus aureus and the coagulase-negative species of the Micrococcaceae family. Four latex agglutination systems (Accu-Staph, SeroSTAT, Staphaurex, and Staphylatex) and two hemagglutination systems (Hemastaph and Staphyloslide) were compared for their performance in the rapid identification of 232 isolates of staphylococci, including 114 of methicillin-resistant S. aureus. Accu-Staph, Staphaurex, and Staphyloslide correctly identified 100% of the methicillin-resistant S. aureus isolates; Hemastaph and Staphylatex, 99.1%; and SeroSTAT, 94.7%. Most reactions were easy to interpret, although 15% of the SeroSTAT reactions were weak. Autoagglutination occurred only with isolates of coagulase-negative staphylococci. False-positive reactions were rare and occurred only with systems which did not detect autoagglutination. Five of these six systems appear to be adequate for the rapid identification of S. aureus, including methicillin-resistant isolates.

Coagulase↗
PubMed2005

Evaluation of the gamma interferon test for diagnosis of paratuberculosis in goats.

The gamma interferon assay was evaluated for diagnosis of paratuberculosis in goats with special emphasis on false positive reactions. Four categories of herds were tested: (A) herds that had a history of paratuberculosis, had given positive Mycobacterium avium subsp. paratuberculosis fecal samples and were vaccinated against paratuberculosis; (B) herds that had been vaccinated but had never shown clinical signs of paratuberculosis nor given positive M. a. paratuberculosis fecal samples; and (C) non-vaccinated herds without paratuberculosis. To extend the analysis of samples from young goats free of paratuberculosis, animals less than 18 months of age from non-vaccinated herds without paratuberculosis, category D, were included. Heparinized blood was stimulated with purified protein derivate (PPD) from M. a. paratuberculosis for 24 h and plasma was assayed for the presence of gamma interferon. Results were recorded as the difference between OD values of PPD stimulated and control samples. Vaccinated animals from herds with paratuberculosis, category A, showed significant higher gamma interferon responses than animals from vaccinated herds without paratuberculosis, category B. In both these groups the responses were correlated to age with higher responses in younger animals. Some of the vaccinated animals in herds without paratuberculosis had a gamma interferon response lasting for several years, which demonstrate a long lasting interference with diagnostic testing in vaccinated goats. Only three of the 121 non-vaccinated animals free of paratuberculosis in category C had responses against PPD (corrected OD values at 0.2, 0.24 and 0.5), and none of the 255 young animals in category D had corrected OD values exceeding 0.2. This indicates that false positive reactions do not appear to the same extent in young goats as in young cattle. We conclude that the low responses of non-infected goats could make the gamma interferon assay useful in monitoring the paratuberculosis status of non-vaccinated herds. However, more information about the early gamma interferon responses of naturally infected goats and the presence of false negative samples are needed.

Animals↗
PubMed1974

Use of immunoperoxidase for the rapid identification of human myxoviruses and paramyxoviruses in tissue culture.

The immunoperoxidase method, using commercially available antisera, was compared with standard virological methods for the identification and typing of 77 isolates of human myxoviruses and paramyxoviruses. Results of typing using neutralization tests and the immunoperoxidase technique were identical for 76 of the 77 isolates. With the immunoperoxidase method there was one false negative reaction, but no false positive reactions. Cross-reactivity between influenza A (soluble) and A(2)/HK antisera with influenza A isolates was noted, but did not interfere with the interpretation of results. It is concluded that the immunoperoxidase method is ideally suited for the rapid identification and typing of common human respiratory viruses on a routine basis. It offers a number of decided advantages over both immunofluorescence and standard virological methods.

Antigens, Bacterial↗
PubMed1996

Bile medium for rapid presumptive identification of group B streptococci.

A bile medium was developed for rapid presumptive identification of beta hemolytic group B streptococci. Of 131 clinical isolates of group B streptococci, 125 (95.4%) yielded positive reaction within 6 h incubation. No false positive reaction was found in 134 clinical isolates of groups A, C, F, and G beta-hemolytic streptococci. The sensitivities of the bile medium, rapid hippurate hydrolysis and modified LAL-1 medium were 95.4, 98.5 and 93.1%, respectively. All three media showed 100% specificity. Therefore, the bile medium provides as an additional medium for rapid presumptive identification of group B streptococci.

Bile↗
PubMed1977

[The phenoloxidase activity in the presence of H2O2, EDTA, and copper (author's transl)].

Investigations performed with cryostat sections of the gut, spleen and lung of the rat have shown, that the substrate of PER H2O2 inhibits the PO activity in dependence of the concentration, and that obvious the PO substrate DOPA is no suitable H2-donator for the PER reaction. Therefore a false positive reaction by the PO proof is not to be expected. Copper sulfat does not influence the PO reaction, but it accelerates melanin formation, which causes an unspecific colouring of the tissue.

Animals↗
PubMed1995

Detection of Brucella abortus antigens by immunoperoxidase histochemical staining of lochia smears.

An immunoperoxidase histochemical staining technique for the detection of Brucella abortus organisms in lochia of brucellosis-infected cows was described. In comparison with the standard culture technique, the former method resulted in 36% false positive and 2.3% false negative reactions, which represents a sensitivity of 82% and a specificity of 94%. False positive reactions are presumably the result of organisms which succumbed during transit. The feasibility of the test in the confirmation of brucellosis is discussed.

Animals↗
PubMed1992

Direct detection of circulating hepatitis C virus RNA using probes from the 5' untranslated region.

Diagnostic testing for hepatitis C virus (HCV) infection currently is based on the presence of anti-HCV antibodies or a positive HCV RNA polymerase chain reaction (PCR) test. Although HCV RNA PCR is a sensitive and specific technique, widespread application is limited. Moreover, HCV RNA PCR is subject to false-positive reactions through contamination and is inherently difficult to standardize and quantitate. To overcome limitations of HCV RNA PCR, we produced both cDNA and riboprobes from a 241 nucleotide sequence of the 5' untranslated region of the HCV genome for slot hybridization. Hybridization was absent using normal human serum, horse serum, or hepatic cellular RNA from noninfected liver. Hybridization occurred predominantly with positive-stranded HCV RNA and was abolished by pretreatment with RNase A. Slot hybridization was performed on serum samples from 60 patients with chronic HCV infection and a positive HCV RNA PCR and 20 patients with liver diseases unrelated to HCV who had a negative HCV RNA PCR. Slot hybridization with cDNA and riboprobes showed concordance with HCV RNA PCR of 95 and 98.3%, respectively. There were no false-positive reactions in controls. The sensitivity of riboprobe hybridization was comparable to that of one stage HCV RNA PCR using 5' untranslated region primers. Riboprobe hybridization with the HCV H strain standard was positive in the dilution corresponding to 10(-6) chimpanzee infectious doses50/ml. The density of the hybridization signals correlated significantly with the mass of an RNA standard extracted from the liver of a patient with HCV infection. The relative quantities of HCV RNA in the sera of selected patients varied and were not correlated with the duration of disease or the histopathological stage. The highest relative quantities were associated with concurrent immunosuppression. We conclude that slot hybridization is a sensitive, specific alternative to HCV RNA PCR that can be directly quantitated using appropriate HCV RNA standards.

Base Sequence↗
PubMed1963

Ovarian hyperemia pregnancy test.

In 310 cases in which a pregnancy test was carried out by injecting serum from the woman into immature female rats and observing the ovaries at autopsy 18 hours later, there were no false positive reactions. Results in three instances were false negative and in two of the three a positive reaction was obtained upon repeat of the test two weeks later.The advantages of using serum for the test are believed to outweigh the convenience of obtaining urine specimens.

Animals↗
PubMedDate not supplied

[Sero-immunologic diagnosis of human African trypanosomiasis: cross reactions of various parasitoses and hyperglobulinemias].

The immunological test: latex agglutination, counter immuno-electrophoresis, ELISA, and immunoperoxydase test, have been applied on the serodiagnosis of african sleeping sickness, and have been compared with each other, with special reference to the cross-reactions in parasitic diseases and hyperglobulinemia. In addition to malaria and leishmaniasis well known interferences, this study gives clear indication of the importance of false positive reactions in active toxoplasma infection. Any how, the serodiagnostic can be worked out from the analysis of responses to various specific antigens, which are always more positive with the homologous antigen.

Animals↗
PubMedDate not supplied

[False reactions in hydatic serology in order to improve its value (author's transl)].

We have studied false reactions in hydatic serology in order to improve its value. We have found false positive reactions in two cases of tumor (hepatic sclerocholangiomatosis and pleural mesothelioma) and among children showing cor's milk protein intolerance when serum is tested with an antigen extracted from ox's lung. As for false negative reactions, they are scarcely due to circulating antigens. We have found, for 34 falsely negative serums, IgG, IgM and above all IgE levels lower than the levels of patients showing a positive serology.

Adolescent↗
PubMed1994

Review of the problems involved in using enzymes in blood group serology--provision of freeze-dried ICSH/ISBT protease enzyme and anti-D reference standards. International Council for Standardization in Haematology. International Society of Blood Transfusion.

Proteolytic enzyme preparations and techniques used routinely in blood group serology for the detection of atypical patient antibodies prior to transfusion vary widely and are often poorly standardised. Recent advances have been made in the use of biochemical methods to standardise and stabilise the potency of the enzyme preparations used. A joint working party of the International Council for Standardization in Haematology (ICSH) and the International Society of Blood Transfusion (ISBT) has investigated possibilities for the provision of standards for the protease preparations and techniques. The specification for these standards was that the performance of enzyme reference preparation in the reference technique should be of equivalent sensitivity to the ICSH/ISBT LISS spin indirect antiglobulin test using a titration series of a reference weak anti-D, and be free from false-positive reactions. The working party circulated materials for evaluation in inter-laboratory trials, followed by a laboratory workshop meeting to achieve agreement on the specification for reference materials and methods. Reference freeze-dried papain at 0.6 azoalbumin units and weak anti-D preparations (91/562) have been prepared and validated to meet these specifications. The performance of a test enzyme preparation in the technique for which it is recommended for use should be at least equal to that of the reference papain preparation, by the reference two-stage technique in terms of sensitivity, using a titration series of the reference anti-D, and freedom from false-positive reactions, using six fresh inert sera. The reference papain and weak anti-D can also be used to calibrate the level of proteolytic activity required in other procedures in blood group serology, such as new technology methods for antibody detection, and automated and microplate cell grouping procedures. These preparations and an agreed method for their use are now available from listed centres as ICSH/ISBT and Food and Drug Administration reference materials.

Blood Grouping and Crossmatching↗
PubMed1979

Analysis of the non-immunological activity of allergen extracts in cutaneous tests.

The technique proposed by the National Institute for Biological Standards and Control, London (NIBSC, 1977) for the control of allergenic extracts for non-immunological activity in skin tests has proved to be both sensitive and useful. We have observed 'false positive' results to substances such as merthiolate or glycerine and also to lyophilised preparations with sugar, notably glucose, as the carrier substance. Other factors studied in 'false positive' reactions to a given extract were pH, osmotic pressure and the presence of traces of endotoxins or histamine. Individually none of these provided satisfactory explanations for the false positive reactions and the use of antagonists or inhibitors of the release of chemical mediators only confirmed the complexity of the non-immunological reaction and the participation of factors other than histamine.

Allergens↗
PubMed1984

Problems in the serodiagnosis of canine brucellosis: dog responses to cell wall and internal antigens of Brucella canis.

Three procedures are commonly used for the serodiagnosis of B. canis infection: 1) The rapid slide agglutination test (RSAT), 2) the tube agglutination test (TAT), and 3) the modified 2-mercaptoethanol tube agglutination test (2ME-TAT). Hemocultures are always essential for diagnosis. The RSAT was developed to provide a presumptive diagnosis rapidly. It has been found accurate in identifying non-infected dogs; however false positive reactions are common due to shared determinants between the surface antigens of B. canis and certain other gram-negative bacteria. The RSAT has recently been modified to include brief reaction of test sera with 2ME (0.2M) prior to adding test antigen. The modification has improved specificity, but it has not eliminated false positive reactions. The TAT and 2ME-TAT are widely used. Although there is good agreement between tests, both suffer from lack of specificity but are valuable in kennels where B. canis has been identified by blood cultures. Agarose gel immunodiffusion (AGID) tests using extracted (SDC or hot PBS) cell wall antigenic complexes reveal precipitins in the sera of infected dogs usually 8 to 12 weeks postinfection (PI) that may persist 5 years. The antigenic complexes consist of at least 3 antigens; one (antigen '2R') appears to possess high B. canis specificity. Sera from noninfected dogs also may react nonspecifically in AGID tests that employ crude SDC or PBS antigenic extracts leading to 'false positive' interpretations. Cytoplasmic antigens gave up to four precipitin lines with sera from B. canis infected dogs. The antigens (protein or glycoprotein) were present in both S and R Brucella cells, but not in other gram-negative organisms examined. AGID tests that employed cytoplasmic antigens revealed precipitins against one or more (usually 2-3) antigens from PI months 4 through 64. In some dogs, precipitins were present 12 months after the bacteremia had ceased, a time when other tests were diagnostically insignificant, or equivocal. No 'false positive' field sera reached with the cytoplasmic antigens.

Animals↗
PubMed1993

Simple solutions to false-positive staphylococcal enterotoxin assays with seafood tested with an enzyme-linked immunosorbent assay kit (TECRA).

The TECRA kit, a commercial staphylococcal enterotoxin visual immunoassay kit, is an enzyme-linked immunosorbent assay system which utilizes polyvalent antisera against staphylococcal enterotoxin types A to E. The test is simple and rapid to perform (4 h) and has therefore been widely used for screening purposes. In this study, the TECRA kit produced a number of false-positive reactions with seafood; 25% of 218 samples of seven types of seafood gave false-positive results, particularly shellfish such as mussels (85%), clams (32%), oysters (23%), winkles (20%), and squid (13%). Some nonshellfish samples also gave false-positive results with the TECRA kit (smelt [20%] and trout [10%]). The substance contributing to the false-positive results differed from true staphylococcal enterotoxins in that it was: (i) heat labile, being completely inactivated by heating for 3 min at 70 degrees C, compared with 5% inactivation of true staphylococcal enterotoxins by the same heat treatment, (ii) in a selective reaction with normal rabbit or calf serum (nonspecific reactions were completely abolished by these sera, whereas staphylococcal enterotoxins were not affected), and (iii) incapable of binding to a copper-chelate Sepharose gel (all of the substance remained in the unbound wash fraction, whereas staphylococcal enterotoxins were quantitatively bound to the gel). The false-positive reactions occurring with seafood were not associated with substances produced by microorganisms, since the bacterial isolates from the samples did not give positive results with the TECRA kit.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1999

[Preliminary studies on microwave irradiation ELISA for diagnosis of Schistosomiasis japonica].

AIM: To explore a fast and highly efficient method for the diagnosis of schistosomiasis japonica. METHODS: Using microwave irradiation ELISA (MWI-ELISA) and fast-ELISA to detect specific antibodies in sera from 118 cases with schistosomiasis japonica, 61 healthy individuals and 12 paragonimiasis cases. RESULTS: The positive rates of schistosomiasis cases were 88.1% (104/118) by MWI-ELISA and 91.5% (108/118) by fast-ELISA, respectively (chi 2 = 0.74, P > 0.05). The false positive reaction of healthy individuals was found in 2 cases(3.3%) by MWI-ELISA and 1 case (1.6%) by fast-ELISA, respectively (chi 2 = 0.34, P > 0.05). No false positive reaction was found in paragonimiasis cases. CONCLUSION: The sensitivity and specificity of the two tests were similar, however, MWI-ELISA was faster than fast-ELISA.

Animals↗