PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “False Positive 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 235 records · Page 13Linked to original sources
PubMed1987

[Causes of error in the study of fibrinogen clumping and the diagnosis of Staphylococcus aureus: Micrococci and Acinetobacter].

Rapid presumptive identification of S. aureus, particularly on the agar slant of biphasic blood culture bottles can be performed by modified slide clumping factor tests. We compared two commercial reagents (Staphyslide and Staphaurex) using strains of "Gram-positive cocci arranged in clusters" (S. aureus, S. epidermidis, Micrococcus) or diplococci-like organisms such as Acinetobacter. Micrococcus and Acinetobacter can be responsible for false-positive reactions with sensitized or not sensitized particles. Control reactions with not sensitized particles or autoagglutination tests in water rather than saline must be performed.

Acinetobacter↗
PubMed1989

A comparison of six epicutaneous devices in the performance of immediate hypersensitivity skin testing.

Six devices commonly used for immediate hypersensitivity epicutaneous skin testing were compared with regard to precision and diagnostic accuracy. Fifteen subjects were tested on the back to 10 mg/ml of histamine phosphate and 50% glycerosaline by prick technique with a smallpox needle (SN), bifurcated needle (BN), Greer "pen" (GP), and blood lancet, and by puncture with the Morrow-Brown needle (MB) and Multi-Test (MT). Five devices were tested in quintuplicate to histamine and once to glycerosaline in each subject; with MT, five histamine and three glycerosaline sites were used. Analysis of the wheal areas obtained with SN, BN, GP, and MB demonstrated comparable degrees of precision (coefficient of variation). The precision of MT was less than the other devices (p less than 0.05). The blood lancet demonstrated intermediate precision. Twenty-two of 45 (49%) of the glycerosaline skin tests performed with MT were falsely positive, significantly more than the other devices (p = 0.0001). We conclude that MB, BN, GP, and SP are comparable devices for use in immediate hypersensitivity skin testing. The low precision and reliability of MT used for testing on the back would appear to make this device less than adequate for diagnostic or research studies. Its high rate of false positive reactions requires caution in interpretation of results when it is used in the clinical diagnosis of allergy.

Adult↗
PubMed1988

The chick chorioallantoic membrane assay: an improved technique for the study of angiogenic activity.

The chick chorioallantoic membrane assay has been used for many years as an in vivo assay of angiogenic activity. However it has been plagued with the problem of a high incidence of false positive angiogenic responses. In this study the conventional chick chorioallantoic membrane assay was compared with a modification of this technique in a series of batches using a total of 100 eggs. False positive reactions were recorded in 32 out of 50 (64%) using the conventional method and only 11 out of 50 (22%) with the modified method (chi 2 = 17.992; p less than 0.001).

Amnion↗
PubMed2000

Plasmodium falciparum histidine-rich protein 2-based immunocapture diagnostic assay for malaria: cross-reactivity with rheumatoid factors.

Recently introduced rapid nonmicroscopic immunocapture assays for the diagnosis of malaria infection are being evaluated for their sensitivity and specificity in various epidemiological settings. A Plasmodium falciparum histidine-rich protein 2 (PfHRP-2)-based assay (ICT) and a Plasmodium-specific lactate dehydrogenase test (OptiMAL) were evaluated for their specificities in different groups of patients who tested negative for malaria infection by microscopy. The patients were selected from different disease groups: rheumatoid arthritis, hepatitis C, toxoplasmosis, schistosomiasis, and hydatid disease. One hundred thirty-three of the 225 patients were positive for rheumatoid factor. Thirty-five of the 133 (26%) rheumatoid factor-positive patients gave a false-positive reaction with the ICT assay, but only 4 of these gave false-positive reactions with the OptiMAL test. Thirty-three of the 35 false-positive specimens became negative when repeat tested with the ICT assay after absorbing out the rheumatoid factor activity. Our study shows that the PfHRP-2-based ICT assay gave a false-positive reaction in 26% of the patients who had rheumatoid factors, but were negative for malaria by microscopy.

Animals↗
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↗
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↗
PubMed1989

Clinical evaluation of a direct fluorescent monoclonal antibody test for detection of Pseudomonas aeruginosa in blood cultures.

A direct fluorescent monoclonal antibody test (DFA; Genetic Systems Corp., Seattle, Wash.) was evaluated for the detection of Pseudomonas aeruginosa in 178 blood culture broths obtained from 128 patients. The DFA identified 44 (98%) of 45 blood cultures positive for P. aeruginosa and was negative in 131 (98%) of 133 blood cultures which grew gram-negative rods other than P. aeruginosa. Upon further investigation, saline suspensions of the organism from the false-negative blood culture were strongly (4+) DFA positive. The false-positive reactions were not due to cross-reactivity, as shown by lack of DFA staining of the non-P. aeruginosa isolates following subculture to agar media. The specificity of the reagent was further demonstrated by directly staining culture isolates including 10 serotypes of P. aeruginosa (all positive) and 57 selected gram-negative bacilli including eight species of Pseudomonas that were not P. aeruginosa (all negative). DFA staining of blood culture broths was easy to perform and read with minimal background fluorescence. The DFA method can be performed in 50 min and appears promising as a rapid method for the identification of P. aeruginosa bacteremia.

Antibodies, Monoclonal↗
PubMed1986

Evaluation of six enzyme immunoassays for antibody against human immunodeficiency virus.

Six commercial enzyme immunoassays (EIA) were evaluated in 6488 serum samples, with immunoblot analysis as the confirmatory test for antibodies against human immunodeficiency virus (HIV). The Abbott and Wellcome tests identified all 163 immunoblot-positive samples correctly, whereas the other tests did not detect 1-3 samples. In AIDS patients (predominantly with antibodies to gp41env) Organon's EIA was less sensitive (p less than 0.05) and Wellcome's more sensitive (p less than 0.05) than the immunoblot assay. In symptom-free anti-HIV-positive subjects (antibodies to almost all viral antigens and high titres of anti-p24gag) all the EIA were significantly (p less than 0.05) less sensitive than the immunoblot assay. The frequencies of false-positive reactions in a "tricky" panel of samples from patients with autoimmune and acute viral diseases and in a blood-donor panel were Abbott 9.5%, 0.42%: Organon 1.7%, 0%; Litton 1.0%, 0.4%; Behring 2.7%, 0.06%; Wellcome 0%, 0%; and Pasteur 0%, 0.02%. The results of a seventh EIA (Dupont) were excluded from the study at the company's request. All six EIA evaluated are suitable tests for anti-HIV screening in samples from patients and blood donors.

Acquired Immunodeficiency Syndrome↗
PubMed1971

False positive Wassermann reaction associated with evidence of enterovirus infection.

A large proportion of high titre Coxsackie B5 complement-fixation tests was detected among sera giving false positive Wassermann reactions during 1969. Echo virus type 9 proved to be the prevailing enterovirus and is one of those which induces the formation of antibody to Coxsackie B5. One case of Echo virus type 9 meningitis is presented which produced a false positive Wassermann reaction and a high titre Coxsackie B5 complement-fixation test. The relationship between Echo virus type 9 infection, Coxsackie complement-fixation test results, and false positive Wassermann reactions is considered significant.

Adult↗
PubMed2005

[IgG heterophile antibody causes false positivity for CA19-9, which is overcome with bovine immunoglobulin].

Immunoassay using antibodies is widely applied to measure various clinical parameters such as tumor markers. However, many mechanisms of interference for this method have been reported. We studied serum sample showing false positive CA19-9 values in the range of 24 to approximately 286U/ml depending on the reagent lots used. PEG-pretreated serum did not show false positivity. Using high performance liquid chromatography (HPLC), the CA19-9 false positive peak was obtained around 160kD, which is the same as IgG. Antibody-coated microbeads, labeled antibody and buffer were used in different combinations between different lots, and the buffer was found to be the cause of false positive findings. The amount of bovine IgG contaminated in bovine serum albumin(BSA) in the reagent buffer markedly differed between lots of BSA, and reagent with a low amount of bovine IgG showed false positive results. Bovine immunoglobulin was superior to mouse IgG in the attempt to avoid a false positive reaction. We concluded that the cause of false positive CA19-9 findings in this serum sample was IgG heterophile antibody, which reacts with both of mouse and bovine IgG. The heterophile antibody had greater affinity to bovine IgG than to mouse IgG. The difference between CA19-9 values obtained by different reagent lots was due to different amounts of bovine IgG contaminated in BSA used in the reagent. Bovine immunoglobulin was superior to mouse IgG in the attempt to absorb the heterophile antibody and avoid false positive reaction in this case.

Animals↗
PubMed1994

Immunohistochemical examination of skin wounds with antibodies against alpha-1-antichymotrypsin, alpha-2-macroglobulin and lysozyme.

The distribution of the proteinase inhibitors alpha-1-antichymotrypsin (alpha 1-act), alpha-2-macroglobulin (alpha-2-m) and lysozyme was analysed immunohistochemically in 27 intravitally acquired wounds, 3 postmortem skin lacerations and 9 specimens of undamaged skin. Intravitally acquired wounds demonstrated distinct positive reactions for all antibodies examined (alpha-1-act 66.6%; alpha-2-m 51.9%; lysozyme 25.9%). However the undamaged skin margins opposite the wound margins also gave positive reactions (alpha-1-act 51.8%; alpha-2-m 37.0%; lysozyme 25.9%). Nearly half of the control cases (specimens of undamaged skin) exhibited weak positive reactions for all 3 antibodies. These could be easily distinguished from the strong positive reactions observed in intravitally acquired wounds. False positive reactions were observed due to contamination resulting from contact with serum components, in cases of advanced autolysis of specimens, and as a result of fixation and drying artefacts. Even though immunohistochemical studies of alpha-1-act, alpha-2-m and lysozyme give some indications concerning wound vitality, they cannot be considered as proof because irrefutable differentiation of true positive and false positive reactions is not possible in all cases.

Humans↗
PubMed1998

Evidence to show that an agent that cross-reacts serologically with Cowdria ruminantium in Zimbabwe is transmitted by ticks.

The serological diagnosis of heartwater based on reactions to the immunodominant Cowdria ruminantium major antigen protein-1 (MAP-1) is impaired by the detection of false-positive reactions. In this study, the prevalence of false-positive reactions on seven heartwater-free farms in Zimbabwe was determined to be 8-94% by immunoblotting against C. ruminantium antigens. The highest prevalence of false-positives on Spring Valley Farm correlated with the presence of Rhipicephalus evertsi evertsi ticks. The other tick species found on these seven farms were Hyalomma truncatum and Hyalomma marginatum rufipes. Rhipicephalus evertsi evertsi ticks collected from Spring Valley Farm and fed on seronegative sheep caused seroconversion in one of two sheep. This sheep developed a mild febrile reaction and C. ruminantium MAP-1 antigen reactive antibodies 3 weeks after the ticks started feeding. Polymerase chain reactions (PCRs), conducted using C. ruminantium-specific primers on ticks collected from the seven farms and on some of the R. e. evertsi ticks that had caused seroconversion in one sheep, were negative. However, some of these ticks gave positive PCRs with DNA primers which amplify a 350 bp DNA fragment of the 16s rRNA gene from all ehrlichial agents indicating the presence of infection with one or more Ehrlichia species. Although attempts to isolate the cross-reacting agent from the sheep were unsuccessful, this study demonstrates that false-positive reactions with the MAP-1 C. ruminantium antigen are associated with agents transmitted by ticks.

Animals↗
PubMed1998

Risk factors for false-positive serological reactions for bovine brucellosis in Saône-et-Loire (France).

Since 1990, unusually high rates of false-positive serological reactions (FPSR) in bovine brucellosis screening have been observed in some countries of the European Union. The aim of this survey was to describe this phenomenon in a highly affected French Department, and to evaluate the links between some individual or herd factors and the occurrence of these FPSR. Before 1990, low backgrounds of FPSR were recorded (individual prevalence rate: less than 0.5 per 10,000). The phenomenon burst during the 1990-91 screening campaign, reached a peak in 1992-93 (50.5 per 10,000), and then decreased until the last studied campaign, 1995-96 (9.1 per 10,000). The phenomenon was transient and sporadic within a herd. At the herd-screening level, four assumed risk factors were isolated: (i) the probability of a herd-screening to be positive was closely and positively linked with the herd screening size; (ii) during a given screening campaign, the prevalence of FPSR decreased from December to November; (iii) the presence of at least one goat on the premises increased the risk for the 1992-93 and 1993-94 screening campaigns; and (iv) a previous FPSR in a given herd appeared to be a weak but significant risk factor. At the individual-animal level, herd size, sex and breed did not seem to be linked with FPSR appearance, while young animals were significantly more affected than older ones. However, global variations in herd or individual prevalences remained unexplained. The lack of link between FPSR and brucellosis is strengthened. The hypothesis of a widely spread causal agent with a low individual host susceptibility and/or a low probability of detecting FPSR animals can be supported by these results.

Animal Husbandry↗
PubMed1982

False-positive stool occult blood tests caused by iron preparations. A controlled study and review of literature.

Stools from 10 male volunteers were tested by Hemoccult and Hematest occult blood methods after the ingestion of ferrous sulfate and ferrous gluconate. The volunteers served as their own controls. The Hemoccult methods had 65% and 50% false-positive reactions while the Hematest had 25% and 65% false-positive reactions after ferrous sulfate and ferrous gluconate, respectively. In vitro testing confirmed that ferrous compounds caused a false-positive Hemoccult slide reaction. Previous studies of the effect of medicinal iron on occult blood tests are reviewed.

Adult↗
PubMedDate not supplied

Comparison of three techniques for the detection of antibodies to double-stranded DNA: immunofluorescence on Trypanosoma gambiense, immunofluorescence on Crithidia luciliae and radioimmunoassay using the Farr technique.

Three techniques for the detection of antibodies against double-stranded DNA were compared: two immunofluorescent (IF) techniques using either Trypanosoma gambiense or Crithidia luciliae as antigen and a radioimmunoassay (RIA) based on the Farr technique. The IF on T. gambiense or C. luciliae gives very similar results but the reaction on C. luciliae is easier to read and to interpret. The use of C. luciliae permits the swift elimination of the two main causes of errors: antibodies against the nucleus of Trypanosomidae and antibodies reacting with the base of the flagella. The RIA appears as a very sensitive test since six sera gave a positive reaction with the RIA and a negative reaction with the IF on C. luciliae. However, the RIA gives in nine cases false positive reactions and in four cases false negative results. Those last four sera contained specific antibodies with low avidity for double-stranded DNA.

Animals↗