'False positive' precipitation reactions to extracts of organic dusts due to a teichoic acid from S. aureus. Techniques.
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Absorption↗
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Results for “False Positive Reactions”
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Presumptive false positive serologic reactions for syphilis in Central America. II. Relation to serum ascorbic acid, riboflavin, alkaline phosphatase, carotene, and vitamins A and E in blood serum.
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Alkaline Phosphatase↗
The rapid serological diagnosis of infectious mononucleosis.
A total of 121 samples of serum collected from 101 patients was tested to determine the sensitivity and specificity of a commercial latex agglutination test for detecting infectious mononucleosis heterophile antibody, a commercial immunofluorescence test for detecting antibody to Epstein-Barr virus capsid antigen and a rapid enzyme immunoassay for detecting antibody to Epstein-Barr virus nuclear antigen. Although the Epstein-Barr virus capsid antigen IgM indirect immunofluorescence test proved to be the most sensitive, false-positive reactions were seen when samples collected from patients with cytomegalovirus, hepatitis A virus, parvovirus and leptospira infection were tested. False-positive reactions were also seen with samples containing rheumatoid factor.
Adolescent↗
Fecal occult blood testing: clinical value and limitations.
Occult blood in the stool can be detected by chemical (guaiac), heme-porphyrin, or immunological methods. Each has advantages and disadvantages, with the guaiac slide test Hemoccult II (SmithKline Diagnostics) remaining the most widely used. Various technical factors affect its clinical performance, most notably whether the slides are rehydrated before processing; hydration increases test sensitivity for colorectal cancer but markedly decreases specificity, resulting in a large number of false-positive reactions that require invasive and expensive colonic workup. Newer immunological tests generally have high sensitivity, but poor specificity remains an important problem. In clinical screening situations, unhydrated Hemoccult has about 50% sensitivity for colorectal cancers and about 98% specificity. Only 5% to 10% of positive reactions prove due to cancer, however, so the large majority of reactive tests are false positives; this is an important weakness of occult blood screening. Slide hydration detects more tumors, but the predictive value of a positive test for cancer drops to only about 2%, which greatly diminishes the appeal of hydration. Sensitivity of occult blood tests for benign colonic polyps is poor, and most polyps found during workup of a positive reaction are actually detected by chance because of high prevalence in the general population. Controlled clinical trials have now documented that periodic occult blood screening produces a relatively small but significant mortality benefit from colorectal cancer--about 15% to 18% for biennial testing with unhydrated Hemoccult. Aggressive annual screening with hydrated Hemoccult may lower mortality by more than 30% but at a very high cost because of poor specificity and very low predictive value. Regular occult blood testing beginning at age 50 has been endorsed by many professional organizations because of the documented mortality benefit, but poor compliance, high costs, and ethical uncertainties seriously temper its justification. Whether to implement widespread occult blood screening remains a difficult societal decision.
Colorectal Neoplasms↗
Laboratoire d'Hygi'ene de la Facult'e de M'edecine de Lyon Universit'e Claude-Bernard, Domaine Rockefeller, 8, avenue Rockefeller, 69373 Lyon Cedex 2 France.
The objective of this study was to investigate the false-positive reactions in the Kline, FTA200 and FTA-ABS tests in acute disseminated lupus erythematosus, polyarthritis and controls. Though the false-positive Kline tests are frequent in autoimmune diseases, false-positive FTA200 when made on non lyophilised treponema are uncommon. On the other hand, when lyophilised treponema are used as substrate for the immunofluorescence, false-positive FTA200 and FTA-ABS are more common in the patients with autoimmune diseases than in controls. The false-positives had two patterns of fluorescence "beaded" or "homogeneous". The present investigation suggests that the false-positive reactions of the beaded type are due to the presence of anti-DNA antibodies in the sera.
Antibodies, Antinuclear↗
False-positive urine beta-HCG in a woman with a tubo-ovarian abscess.
Modern urine beta-human chorionic gonadotropin (HCG) assays that use enzyme-linked immunosorbent assay (ELISA) technology are sensitive and specific for diagnosing pregnancy, both intrauterine and ectopic, and have become indispensable to the practice of Emergency Medicine. A urine HCG test is often relied on by the Emergency Physician as a critical component in the diagnostic regimen of a patient with a possible ectopic pregnancy. We report a case of a false-positive urine beta-HCG test in a patient with a ruptured tubo-ovarian abscess. Though false-positive pregnancy tests with tubo-ovarian abscesses have previously been reported with older methods of HCG detection, we believe that this is the first case where the pregnancy test was the modern ELISA type. The mechanism for the false-positive reaction in this case is unknown, but time may show that the ELISA test kit, like its predecessors, may occasionally give a false-positive reaction in this class of patients.
Abscess↗
Evaluation of equine infectious anemia virus core proteins produced in a baculovirus expression system in agar gel immunodiffusion test and enzyme-linked immunosorbent assay.
Equine infectious anemia virus (EIAV) core proteins (Gag and p26) obtained from a baculovirus expression system were used in agar gel immunodiffusion (AGID) and enzyme-linked immunosorbent assay (ELISA) antigens to test seventy-six horse sera. Those sera showed false-positive reaction in AGID test using Nisseiken antigen. However, none of them showed false-positive reaction with both of the expressed antigens. The 76 horse sera were also tested by ELISA. The sera gave a high background in ELISA using Nisseiken antigen. Gag and p26 reacted strongly against positive sera from horses immunized with Nisseiken antigen.
Animals↗
Polymyxin-coagulase-mannitol-agar. I. A selective isolation medium for coagulase-positive Staphylococci.
A selective, differential plating medium was developed for the isolation and identification of coagulase-positive and mannitol-fermenting staphylococci. Coagulase produced by growing Staphylococcus aureus caused an opaque zone of fibrin to form around each colony. Several strains of S. aureus produced a visible coagulase reaction by 8 hr, and all strains gave a positive reaction before 12 hr. Mannitol fermentation was usually observed between 12 and 36 hr. Rabbit serum was filtered through Sephadex G-100 to obtain plasmin- and plasminogen-free coagulase-reacting factor (CRF). False-negative reactions, caused by staphylokinase and staphylococcal Müller factor action on plasminogen, were eliminated when this CRF was used. False-positive reactions by lipolytic, coagulase-negative staphylococci were reduced, since gel filtration removed the serum lipoprotein which served as a primary source of opacity. The addition of 75 mug of polymyxin B per ml selectively retarded the growth of S. epidermidis and minimized false-positive reactions caused by citrate-utilizing gram-negative rods. The preparation, characteristics, and use of the medium are presented.
Agar↗
Urine protein determination in dogs and cats: comparison of dipstick and sulfasalicylic acid procedures.
Protein levels in urine specimens from 91 dogs and 65 cats were evaluated by sulfasalicylic acid precipitation (SSA) and dipstick methods. The dipstick frequently yielded reactions for protein that were greater than the level of protein indicated by SSA (i.e., false positive reactions), although no false negative reactions for protein were noted. All urine specimens with protein levels equal to or greater than 100 mg/dl by SSA had dipstick results of 3 +. Results of this study suggest that dipstick analysis for urine protein is an adequate screening procedure for the selection of urines for quantitative analysis of protein and creatinine to assess proteinuria.
Journal Article↗
Platelet crossmatching for kidney transplants by flow cytometry.
Although flow cytometry crossmatching is now performed by many kidney transplant centers, it yields a high false-positive rate, as evidenced in the present series by a 71% one-month success rate despite a positive crossmatch. In an attempt to reduce false-positive reactions while retaining the sensitivity of the flow cytometer, platelets were tested as targets. Whereas flow cytometry with T cells was not correlated with one-month failure rates, retrospective platelet crossmatching by flow cytometry showed that kidney failure within one month occurred in 53% of 19 patients with a positive platelet crossmatch compared with 15% of 48 patients with a negative platelet crossmatch. (P less than 0.002). Statistical significance in one-month outcome was also obtained when only first transplant patients were analyzed (P less than 0.04). The present results suggest that crossmatching with platelet targets may be a simpler way to avoid early primary nonfunction while minimizing false-positive reactions.
Blood Grouping and Crossmatching↗
Use of the recombinant chimera proteins, LacZ-Env and Gag-Env, for immunological studies on HIV-1 infection.
To use Env proteins as antigens for detection of the human immunodeficiency virus type-1 (HIV-1) antibodies, we attempted to overexpress the Env proteins in Escherichia coli. To study the epitopes in the Env proteins recognized by the sera of HIV carriers, various regions of the proviral DNA encoding the Env region were fused to the 3' end of the lacZ gene. The immunoblotting analysis of the LacZ-Env(512-611) and LacZ-Env(721-826) proteins with the 41 positive sera revealed that the former and the latter immunologically reacted with 100 and 78% of the sera, respectively. To avoid rare false-positive reactions due to the LacZ moiety of the fusion protein, we attempted to express the Env(512-611) alone or Gag-Env(512-611) under the control of bacteriophage T7 promoter. Although we could express only a low level of the Env(512-611) peptide in E. coli, we succeeded in producing large amounts of the Gag(121-406)-Env(512-611) and Gag(308-406)-Env(512-611) proteins as chimeric proteins. Both of these chimera proteins strongly reacted with the 41 positive sera. We purified these proteins and analyzed the immunological reactivity by dot blot with the 60 positive sera and the 84 normal sera. As little as 20 ng of the dotted proteins was enough for the reaction with the positive sera, whereas as much as 320 ng of them did not show false-positive reactions with the normal sera. We obtained highly purified Gag-Env proteins with highly specific seroreactivity, which should be useful for diagnosis and prognosis.
AIDS-Related Complex↗
Matrix effects in clinical immunoassays and the effect of preheating and cooling analytical samples.
Immunological reactions are influenced by various factors including antigens, antibodies and other variables. We focused on two items: i) matrix effects, especially of detergents and ii) temperature effects: preheating sera, especially effects on rheumatoid factor (RF) measurement and false-positive reactions in ELISAs, and cold storage of sera, especially effects on complement. Among various additives, detergents affected the agglutination reaction for fecal hemoglobin and hepatitis B surface (HBs) antigen. Some of the detergents examined abolished these antigenicities, however, polyethylenglycols enhanced the reactions. Heat-inactivation of sera at 56 degrees C for 30 min was employed in serological testing. However, in RF measurement, 10 min of preheating was sufficient to abolish C1q (subcomponent of C1), which could participate in the agglutination reaction. In ELISA for antibodies, false-positive reactions were caused by preheating sera. By the analyses of assays for antibodies to hepatitis C virus (HCV) and cardiolipin, it was found that they were induced by immunoglobulin G (IgG) modified by preheating. Cold storage induced activation of complement (cold activation) in anti-HCV antibody positive sera. CH50 titers in the sera were lowered by one cycle of freezing at -20 degrees C and thawing, and the decrease was affected by the containers.
Autoantibodies↗
Streptococcus pyogenes streptolysin O as a cause of false-positive CAMP reactions.
The synergistic hemolysis of sheep erythrocytes in the CAMP reaction by the sequential action of staphylococcal beta-lysin and the CAMP factor of group B streptococci is the only known function of this extracellular product of group B streptococci. The reaction forms the basis of the CAMP test used to identify group B streptococci because the CAMP factor is believed to be restricted to this group of organisms. However, on occasion other streptococci, notably group A streptococci, may produce a similar synergistic lysis of sheep erythrocytes. The nature of the synergistic lytic factor of group A streptococci responsible for this sequential hemolysis was investigated in a tube CAMP reaction system. The properties of this synergistic lytic factor were found to correspond to those of streptolysin O of group A streptococci. The synergistic lytic factor, like streptolysin O, was produced during the logarithmic phase of growth; the activity was increased by reducing agents and greatly decreased or abolished by heat, trypsin, cholesterol, and anti-streptolysin O, and it was immunogenic in rabbits. This would suggest that the synergistic hemolysis seen in the CAMP reaction system with group A streptococci is due to the action of those small amounts of streptolysin O which remain unoxidized and thus have a capacity to lyse the fragile beta-lysin-treated sheep erythrocytes.
Animals↗
Analysis of specific IgE and IgG subclass antibodies for diagnosis of Echinococcus granulosus.
The potential roles of specific antibodies of different immunoglobulin G (IgG) subclasses and IgE in serological diagnosis of cystic echinococcosis (CE) were investigated by an enzyme linked immunosorbent assay (ELISA) based on Antigen 5 (Ag5). Presence of IgG1 was demonstrated in all sera from 58 patients with CE. The most discriminatory and specific antibodies found in this study belonged to IgG4 and IgE. Only one false-positive reaction was observed with IgG4 and no IgE cross-reactivity occurred with 40 sera from healthy controls. In 36 sera from patients infected with parasites other than CE two false-positive reactions with IgG4 were observed but none occurred with IgE. In immunoblotting, it was shown that IgG1 subclass was responsible for cross-reactivity of human antibodies that reacted with a 38 kDa subunit of Ag5. IgG4 and IgE antibodies could not recognize the 38 kDa subunit and under non-reducing conditions reacted with the 57 kDa subunit without any cross-reactivity to other parasites. The results demonstrated that IgG4 and IgE are the most important antibodies for serological diagnosis of hydatid cyst in an Ag5 based immunoassay system.
Adult↗
Comparison of a miniaturized culture test and sheep blood agar for the recovery of Group A streptococci from throat cultures.
A miniaturized culture test (strep test) was compared with conventional sheep blood agar (SBA) for the detection of Group A streptococci (GAS) from throat swabs. A total of 355 throat cultures were obtained in duplicate from symptomatic children and assessed by the two methods after overnight incubation. GAS were detected in 109 specimens by the strep test, in 100 specimens by SBA and in 118 specimens by both methods. There was no significant difference between the recovery rate of GAS by the strep test (92.4%) and SBA (84.7%) (0.1 greater than P greater than 0.05). The strep test was 85.2% specific for detection of GAS. The rates of false positive and false negative reactions with the strep test were 24.3 and 4.3%, respectively. Beta-hemolytic streptococci other than Group A, Staphylococcus aureus and alpha-hemolytic streptococci produced false positive reactions. The viability of GAS on the strep test was also tested. GAS were recovered from 27 of 28 (96.4%) strep tests at 24 hours and 25 of 27 (92.6%) tests at 72 hours after inoculation. These results indicate that strep test is as sensitive as the conventional SBA method in recovering GAS. The strep test is simple to use, is easy to interpret and has a long shelf life. Because of the high rate of false positive results (24.3%), this test may not be the best alternative method to SBA for use in office practice.
Agar↗
Evaluation of the Biolog system for the identification of Bacillus anthracis.
The potential of the Biolog system for the identification of Bacillus anthracis was evaluated. In-house generated databases allowed the correct identification of 19 of 20 isolates of B. anthracis within 24 h. Five strains of the closely related B. cereus/thuringiensis group were misidentified as B. anthracis. For this reason the test could only serve as a primary screen with further testing being required to confirm identity. In addition 20% of all the strains of bacilli examined during the study gave unreadable reaction profiles due to false-positive reactions.
Bacillus anthracis↗
Heterotypic antibodies in Liberian sera causing anomalous reactions when using a commercial haemagglutination test for hepatitis-B surface antigen.
Agglutinins reacting with normal and tanned sheep erythrocytes were the probable cause of false positive reactions given by 51 of 214 Liberian sera when using a commercial passive-haemagglutination test for hepatitis-B surface antigen. Absorption showed these agglutinins to be identical to those described earlier in Nigerian sera. Rheumatoid factor and anti-sheep-serum antibodies although present in 12 and five per cent respectively of all sera were not responsible for any false positive reactions. The practical conclusion is that such tests, based on sheep erythrocytes are unsuitable for screening this population.
Antibodies, Heterophile↗
Discrimination of Antibodies to Hepatitis B surface antigen from antibodies to inherited serum protein variants in immune sera of human and animal origin.
Antisera to hepatitis B surface (HBs) antigen, both of human and rabbit origin, have been examined. The anti-HBs serum derived from a multiply transfused patient did, in addition, contain antibodies directed against the inherited beta-lipoprotein antigen Ag(x), whereas one of the rabbit immune sera also contained antibody to the inherited Lp(a) antigen. Thus, in human, as well as in animal anti-HBs sera, antibodies to inherited normal serum antigens may cause false positive reactions. This problem may be overcome by absorption procedures if appropriate control systems are available. False positive reactions caused by the Ag(x) antigen may also be avoided by use of agarose as supporting medium for the test, as Ag(x) precipitin lines do not appear in this medium. An undialysable high molecular weight component may be obtained from Oxoid "Ionagar" by washing. When this is added to agarose the Ag(x) antigen reaction appears also in this medium.
Absorption↗