PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “False Negative Reactions”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 199 records · Page 11Linked to original sources
PubMedDate not supplied

Factors affecting the results of T-2 mycotoxin ELISA assay.

Certain substances in the sample may increase or decrease the reaction between the enzyme and substrate in ELISA assays. During a survey of T-2 trichothecene in food and animal feed 75% of milled grain samples gave a higher O.D. value in competitive T-2 toxin ELISA than the negative control. In samples spiked with small quantities (10 micrograms/kg) of T-2 toxin this type of reaction resulted in underestimates of toxin content. However, the effect was weak and, owing to the high sensitivity of the assay, it did not result in false negative reactions. The low efficiency of the carrier solvent and natural peroxidases in food and feed were considered to be the cause of the inaccurate reactions. A few fermented and processed foodstuffs and feed gave positive results in the T-2 toxin ELISA assay, but verification of the results by gas chromatography (GC) showed that the reactions were false. Certain substances in the samples destroyed or decreased the enzyme activity. False positive reactions can be distinguished from correct ones by retesting the extracts in different dilutions.

Animal Feed↗
PubMed1988

Comparative study of three immunoassays for detection of immunoglobulin M antibodies against Toxoplasma gondii.

Immunoglobulin M antibodies against a major serological antigen (Mr 6 kD) were detected in human sera by indirect ELISA, antibody capture ELISA, and immunoblot test. In contrast to indirect ELISA, the immunoblot test gave no false positive reactions, not even with those sera containing a high level of rheumatoid factor. However, the immunoblot test gave false negative results with sera which gave positive results in both ELISA tests. The antibody capture ELISA gave no false negative reactions. All positive sera except one reacted specifically with Toxoplasma gondii antigens.

Animals↗
PubMed1991

Evaluation of 29 monoclonal and polyclonal antibodies used in the diagnosis of pituitary adenomas. A collaborative study from pathologists of the Club Français de l'Hypophyse.

Fifteen polyclonal antibodies (pAbs) and 14 monoclonal antibodies (mAbs) directed against hGH, hPRL, beta hFSH, beta hLH, beta hTSH and alpha-subunit were assessed by five different laboratories on normal and adenomatous pituitary tissues. This study aims at providing pathologists with a selected panel of antisera suitable for diagnosis, and appreciating the interest of the recently introduced mAbs. All the anti-hGH Abs proved to be specific (3 pAbs and 4 mAbs); three mAb out of four gave a few false-negative reactions. Three out of six polyclonal anti-hPRL showed cross-reactivity with hGH; anti-hPRL mAbs gave a strong staining with no false-negativity detected so far. MAbs proved to be more efficient for detecting glycoprotein hormones and alpha subunit than pAbs, which, in several cases, gave widespread cross-reactivity. This lack of specificity could explain the noticeable discrepancies reported so far in the appraisal of gonadotropic and somatoprolactinic adenomas.

Adenoma↗
PubMed2002

Highly sensitive multiplex assay for detection of human immunodeficiency virus type 1 and hepatitis C virus RNA.

Various nucleic acid assays have been developed and implemented for diagnostics and therapeutic monitoring of human immunodeficiency virus type 1 (HIV-1) and hepatitis C virus (HCV) infections. The high-throughput, semiautomated assays described here were developed to provide a method suitable for screening plasma specimens for the presence of HIV-1 and HCV RNAs. Three assays were developed: a multiplex HIV-1/HCV assay for simultaneous detection of HIV-1 and HCV, and discriminatory assays for specific detection of HIV-1 and HCV. The assay systems utilize three proprietary technologies: (i) target capture-based sample preparation, (ii) transcription-mediated amplification (TMA), and (iii) hybridization protection assay (HPA). An internal control is incorporated into each reaction to control for every step of the assay and identify random false-negative reactions. The assays demonstrated a sensitivity of at least 100 copies/ml for each target, and they detected with similar sensitivity all major variants of HCV and HIV-1, including HIV-1 group O strains. Assay sensitivity for one virus was not affected by the presence of the other. The specificity of these TMA-driven assays was >or=99.5% in both normal donor specimens and plasma containing potentially interfering substances or other blood-borne pathogens. Statistical receiver operating characteristic plots of 1 - specificity versus sensitivity data determined very wide analyte cutoff values for each assay at the point at which the assay specificity and sensitivity were both >or=99.5%. The sensitivity, specificity, and throughput capability predict that these assays will be valuable for large-volume plasma screening, either in a blood bank setting or in other diagnostic applications.

Blood Donors↗
PubMedDate not supplied

Reporting the results of human immunodeficiency virus testing.

We conducted a pilot study of potential sources of incorrect laboratory reports of human immunodeficiency virus type 1 testing using blind proficiency testing. Sets of three serum samples, including one serum sample with negative reactions in antibody tests, one serum sample with positive reactions, and one that gave false-positive results with certain testing kits, were sent as routine patient specimens to testing laboratories. Half the laboratories reported the serum sample positive for human immunodeficiency virus antibodies as "indeterminate"; one laboratory rendered a final positive report without supplemental testing. On the report forms, the actual laboratory results were often obscured and intermingled with information, sometimes incorrect, such as identifying the agent as "HTLV-III" (human T-cell lymphotropic virus type III) and advising that a test with positive results is evidence of exposure to the virus. Many of these reports have the potential to confuse, rather than to enlighten, the requesting physician.

AIDS Serodiagnosis↗
PubMed1985

Enzyme-linked immunosorbent assay for mumps IgM antibody: comparison of IgM capture and indirect IgM assay.

We have established two enzyme-linked immunosorbent assays (ELISAs) for detection of mumps IgM antibody, i.e., indirect IgM ELISA and IgM capture ELISA, for serodiagnosis of recent mumps infection. In the latter method, peroxidase-conjugated monoclonal antibody to mumps virus was employed. Both methods detected mumps antibody of IgM class only in serum fractions separated by centrifugation through a sucrose density gradient. Optical density values given by both ELISAs were correlated for most sera examined. Indirect IgM ELISA, however, gave a false positive reaction for sera containing both rheumatoid factor and mumps IgG antibody, while giving a false negative reaction for sera containing high titers of mumps IgG antibody. This technique was, therefore, less reliable than IgM capture ELISA. IgM antibody detectable by IgM capture ELISA was present in all patients with mumps by the fifth day of illness and persisted for up to 3 mth in most and up to 5 mth in same cases.

Antibodies, Monoclonal↗
PubMed2004

Bifidobacterium lipoteichoic acid and false ELISA reactivity in aspergillus antigen detection.

A major difficulty with the detection of circulating galactomannan, a cell-wall polysaccharide released by Aspergillus sp during growth, in the serodiagnosis of invasive aspergillosis is the occurrence of false-positive ELISA results, especially in neonates and infants. On the basis of molecule similarity, we postulate that a lipoteichoic acid of Bifidobacterium sp can act as epitope for the monoclonal antibody used in the ELISA. The neonatal gut is heavily colonised with Bifidobacterium sp and these bacteria or their lipoteichoic acid might cause ELISA reactivity with serum after translocation because of immaturity of the intestinal mucosa. If our hypothesis is correct, we might find a method to discriminate between false-positive and true-positive ELISA results and thereby prevent unnecessary pre-emptive treatment of patients.

Antibodies, Monoclonal↗
PubMedDate not supplied

The accuracy of tuberculin skin tests: self-assessment by adult outpatients.

Tuberculin skin testing is an accurate, inexpensive screening procedure for detecting tuberculosis infection. The return visit needed to interpret the reaction is inconvenient, costly, and may contribute to under-utilization of the test. Although some clinicians ask patients to read their own purified protein derivative (PPD) test results, patient accuracy and the degree of teaching needed to learn this skill are unclear. This study evaluated the accuracy with which 145 outpatients read their own Mantoux skin test (PPD) reactions and reported by postcard after brief training by nurse practitioners. A total of 89 instructed patients returned postcards and also returned for clinician readings; 46 submitted postcards without returning; 7 returned but did not complete postcards; and 3 neither returned postcards nor returned for readings. Ten of 135 postcards were uninterpretable. For 81 subjects with both interpretable tuberculin self-assessment postcards and clinician readings, overall PPD classification agreement was 88 percent; Kappaw = +0.905 (P less than .001). Compared to clinician readings, 1 of 53 patients falsely reported a positive reaction (greater than or equal to 10 mm) and 2 of 25 patients falsely reported negative PPD readings (0-4 mm). There was 100 percent agreement between postcard readings and clinician classifications in a subgroup of patients (N = 26), prospectively identified by nurse practitioners as capable of accurate tuberculin self-assessment. Inter-clinician reading agreement (N = 37) was 89 percent; Kappaw = +0.943 (P less than .001). The brief standardized teaching protocol described can enable most patients to measure and report their PPD results. Study results suggest thatpostcard reports, especially negative ones, from a subgroup of patients selected for their skill in measuring their initial PPD wheal and ability to paraphrase instructions, might be substituted for clinician readings.

Ambulatory Care↗
PubMed1989

Diagnostic usefulness of five screening assays for HIV in an east African city where prevalence of infection is low.

Five commercial screening assays for HIV-1, evaluated for their usefulness in detecting infection in high-risk groups in the East African country of Djibouti, produced varying degrees of performance when compared to Western blot and immunofluorescence confirmatory assays. In this population with a low prevalence of HIV infection (16/599), two enzyme-linked immunosorbent assays (ELISA; Abbott and Elavia) and two rapid assays (cambridge latex agglutination and Du Pont's HIV-CHEK) exhibited less than optimal sensitivities. However, with the exception of Elavia, these assays displayed excellent specificities. The fifth test (Serodia gelatin agglutination) produced the highest sensitivity (0.938) and negative predictive value but the lowest specificity and positive predictive value of all five tests. False positive reactions, which occurred only with the Elavia and Serodia tests, could not be explained on the basis of early infection in patients or cross-reactions with the related retroviruses HIV-2 and HTLV-I. We conclude that none of the five tests alone is sufficient in this testing situation, but that a combination of tests could satisfy most requirements for identifying HIV-1 reactive and non-reactive sera.

AIDS Serodiagnosis↗
PubMed1990

[Prevention of false results in tests for occult blood in feces].

The HaemoQuant test and the immunological tests are not devoid of problems so that the (pseudo)peroxidase-sensitive tests are anything but obsolete. Most of the tests are nowadays sold with reduced sensitivity, with the risk of false-negative results. Nevertheless, they can yield false-positive results without a strict dairy-and-vegetable diet in which all components have undergone a heat inactivation (cooking, baking, pasteurization). Uncooked wheat bran reacts strongly, but even liberal use of cooked bran never produced a positive reaction with the sensitive 'Occultest'. Even if thoroughly cooked, all meat, except that of fish with white meat, can elicit a positive reaction. Most leaflets of commercial tests should be thoroughly revised. Also a misleading presentation of a positive reaction can be a source of errors.

Diagnostic Errors↗
PubMed1975

Evaluation of a selective medium for hydrogen sulfide production by salmonella.

An evaluation was made of Padron-Dock-Stader sulfide (PDS) agar for the rapid detection of Salmonella and Arizona microorganisms in foods. Analysts from 9 Food and Drug Administration District laboratories determined the reaction of 638 Salmonella cultures, 30 Arizona cultures, and 1754 non-Salmonella and non-Arizona cultures isolated from 157 food samples in PDS agar. The degree of positive reactions of these cultures in this agar was scored on a scale of "-" to "+++". The highest percentage of Salmonella isolates (64.1%) was in the category of +++ reactions. Progressively lower percentages of Salmonella isolates occurred in the more negative reaction categories. The highest percentage of Arizona isolates (66.7%) occurred in the intermediate ++ category. The majority of non-Salmonella and non-Arizona isolates occurred in the minus (41.0%) and plus or minus (44.8%) categories. Advantages of using the PDS agar are that it is simple to use, requires no specialized training or equipment, and alerts analysts to those Salmonella cultures which produce atypical reactions in triple sugar iron agar particularly the lactosepositive Salmonella. However, in this study the occurrence of false-negative reactions ranged from 4.3 to 13.9% for Salmonella and from 0 to 6.7% for Arizona, according to the criteria used to interpret the reactions in PDS agar.

Cells, Cultured↗
PubMed1985

Ca2 and Ca3. New monoclonal antibodies evaluated as tumor markers in serous effusions.

Ca2 and Ca3 are new monoclonal antibodies of IgG1 class, directed against the Ca antigen, a mucus-type glycoprotein expressed on the surface of a wide range of malignant human cells and certain specialized normal epithelia. These antibodies were produced by immunization with purified preparations of the Ca antigen. They were tested to assess their value in the diagnosis of malignant effusions. Immuno-alkaline-phosphatase staining was used. Smears of pleural and peritoneal effusions were chosen to show: undoubted malignant cells of various types; and mesothelial cells in effusions from cases in which cancer was not in question. The Ca2 antibody, at 1 in 20 dilution of the culture supernatant, was the most specific, giving no reactions with benign mesothelial cells from any of the 35 cases tested. Malignant cells were clearly stained in 35 of 40 cases of carcinoma or mesothelioma. The staining was negative in two cases of oat cell bronchial carcinoma, and in three of four cases of carcinoma of the colon. Ca3 gave similar, but somewhat stronger, reactions with carcinoma cells, but was less specific, reacting weakly with mesothelial cells in 8 of 35 benign effusions. Because the false-negative reactions given by the Ca series of antibodies are to some extent complementary to those given by monoclonal antibodies directed against the carcinoembryonic antigen (CEA), a combination of Ca2 and anti-CEA is recommended as a most useful addition to the normal cytologic examination of effusions.

Antibodies, Monoclonal↗
PubMed1997

[Contact allergy for corticosteroids].

Contact allergy to corticosteroids is not rare. In some studies prevalence rates up to 6% have been observed among patients suspected of allergic contact dermatitis. Hypersensitivity occurs especially in individuals who have been suffering for years from atopic dermatitis, contact dermatitis of the hands and feet, or stasis dermatitis caused by chronic venous insufficiency. The clinical picture is rarely that of acute allergic contact dermatitis, because the reaction is mitigated by the anti-inflammatory properties of the corticosteroid itself; the diagnosis must be suspected when eczema does not improve or spreads during topical corticosteroid therapy. Application to the mucous membranes less frequently leads to sensitisation. Most such cases are caused by nasal sprays containing tixocortol pivalate or budesonide. Oral or parenteral administration of corticosteroids to sensitive individuals causes exacerbation of pre-existing contact dermatitis or widespread allergic cutaneous drug reactions. Allergological investigation with corticosteroids presents some specific problems, the most important being occurrence of false-negative reactions. Nevertheless, most sensitive patients can be identified by testing the 'indicator' allergens, budesonide and tixocortol pivalate, which should be added to the routine series of contact allergens. Cross-reactions to other corticosteroids occur frequently. This should be taken into account when prescribing alternative corticosteroid preparations.

Administration, Topical↗
PubMed1992

[Replacement of Kathon CG by Euxyl K 400 in cosmetics; from the frying pan into the fire?].

The recent negative publicity on the cosmetics preservative Kathon CG has made many cosmetic manufacturers look for safer alternatives. The most popular substitute appears to be Euxyl K 400, containing phenoxyethanol and methyldibromoglutaronitrile. Unfortunately, this preservative also induces allergic reactions to cosmetics and (at least in the Netherlands) to 'moist toilet paper'. Therefore, in cases of apparent reactions to cosmetics and of eczema ani, allergy to methyldibromoglutaronitrile should be suspected. Testing the finished products often results in false-negative reactions, and consequently the allergen (suggested concentration 0.05% in petrolatum) should preferably be tested separately.

Cosmetics↗
PubMed1998

Development of internal controls for PCR detection of Bacillus anthracis.

This work describes the development and evaluation of a multiplex polymerase chain reaction (PCR) for the detection of Bacillus anthracis strains harbouring plasmid pX02. The multiplex also incorporated an internal control (IC) to avoid false negative reactions. Internal controls consisted of plasmids containing modified PCR target sequences, corresponding to the capC and BA813 genes of B. anthracis, which were then co-amplified with the original target sequences using the same set of amplimers. The initial IC construct comprised of an internally deleted form of the genomic target sequence cloned into pUC19. A series of nested DNA fragments corresponding to the 23S rRNA sequences of Bacillus cereus were then subcloned into the point of deletion, producing a number of IC constructs with similar sequences but increasing product size on PCR amplification. Neither the presence of IC DNA template or IC PCR product size affected the specificity or non-specific cross-reactivity of the original PCR assay. The concentration of IC was critical, too much IC DNA template would out compete the genomic DNA template, thus giving a false negative result. However, when the concentration of IC was optimal assay sensitivity was not compromised.

Bacillus anthracis↗
PubMed1975

Which techniques should be used to screen blood donations for hepatitis B surface antigen?

Preservation of all donor sera already tested for Hepatitis B surface antigen (HBsAg) by counterimmunoelectrophoresis (C.I.E.P.) allowed C.I.E.P., reversed passive haemagglutination (R.P.H.A.), and radioimmunoassay (R.I.A.) to be evaluated as screening techniques. Out of 165 811 donors tested for the first time 207 were found by C.I.E.P. to be positive for HBsAf-a prevalence of 0-12%. At the next donation 10 of those apparently negative on first screening were HBsAg positive by C.I.E.P., and nine of these were shown by retesting with R.P.H.A. and R.I.A. to have been positive at the earlier donation. These nine false negatives caused four cases of transfusion-transmitted HBsAg-positive hepatitis. On comparative screening of 22 239 donations C.I.E.P. detected 27 sera positive for HBsAg, R.P.H.A. 39, and R.I.A. 41. Thus R.I.A. increased the detection rate by more than half over C.I.E.P. From these 14 further false-negative donations by C.I.E.P. six cases-one fatal-of HBsAg-positive hepatitis occurred. The number of false positive reactions when using R.P.H.A. or R.I.A. for screening was less than 1%. As many as 700 donations in one day have been tested by R.P.H.A. or R.I.A. R.P.H.A. is faster and less expensive than R.I.A., but R.I.A. is more objective. Either R.P.H.A. or R.I.A. should replace C.I.E.P. as the routine method of screening donor sera for HBsAg.

Blood Donors↗