Misinterpretation and misapplication of p values in antibody identification: the lack of value of a p value.
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Antigen-Antibody Reactions↗
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Clinical evaluation of three rapid methods for the detection of significant bacteriuria.
Random urine specimens (848) were screened for significant bacteriuria by using the 30-min Lumac (3M, St. Paul, Minn.), the 2-min Bac-T-Screen (Marion Laboratories, Inc., Kansas City, Mo.), and the 13-h AutoMicrobic system (AMS) urine identification card (Vitek Systems, Inc., Hazelwood, Mo.). MacConkey and 5% sheep blood agar plates were inoculated with a 10(-4) dilution of urine and used for the reference method. Bac-T-Screen results were uninterpretable for 9.1% of the specimens owing to either urine sample pigmentation (5.3%) or clogging of the filter (3.8%). Screen-negative urine specimens made up 49.6, 57.2, and 48.5% of the total number of specimens evaluated with AMS, Lumac, and Bac-T-Screen, respectively. False-positive results with Lumac and Bac-T-Screen were 20.6 and 22.3%, respectively. False-negative results for cultures with greater than or equal to 10(4) CFU/ml were 22.0% with AMS, 29.4% with Lumac, and 25.5% with Bac-T-Screen, and false-negative results for cultures with greater than or equal to 10(5) CFU/ml were 29.6% with AMS, 9.9% with Lumac, and 7.0% with Bac-T-Screen. For each system, greater than 70% of false-negatives at greater than or equal to 10(5) CFU/ml consisted of mixed or pure cultures of common contaminants. With any of these screening methods, a clinically significant isolate at greater than or equal to 10(5) CFU/ml would rarely be missed (less than or equal to 1.7% for all systems). A cost-effective and rapid approach to urine microbiology could consist of screening out negative specimens by either Lumac or Bac-T-Screen and processing only screen-positive specimens by the AMS.
Adult↗
Usefulness of LAL assay for rapid detection of gram-negative bacteriuria.
LAL assay is a rapid and reliable and easy to perform and interpret urine screen for clinically significant gram-negative bacteriuria. Chromogenic assays are rapid (5 min) and obviate problems associated with gel endpoints, such as inadvertant dissolution of the gel, either during incubation or reading. LAL urine screening is characterized by both high positive and negative predictive values. LAL urine assay identifies gram-negative urinary tract infections by measuring urine endotoxin content as an index for significant numbers of urinary tract pathogens, thus eliminating large numbers of false-positive tests characteristic of other urine screening methods. Screening urine for greater than or equal to 10(5) CFU/ml appears to be an acceptable criterion for defining a UTI in patient populations with low prevalence rates (2-10%). Thus, LAL urine assay may have potential usefulness for screening of asymptomatic populations, such as pregnant women and the elderly.
Bacteriuria↗
Quantitative assessment of alcohol-provoked flushing.
Objective measurements of temperature and blood flow changes by telethermometry and laser Doppler velocimetry (LDV), respectively, were performed continuously in normal subjects after they ingested 0.4 g/kg of ethanol in a volume of 300 mL. Cutaneous temperatures were interpreted by the change in malar thermal circulation index (delta MTCI) method. Both the delta MTCI method and LDV output correlated significantly with the presence of flushing. The delta MTCI method also correlated significantly with LDV output, indicating that the intensity of the flushing reaction can be assessed by both methods. The sensitivity, specificity, and predictive value of a positive result were greater with the LDV method. The time to maximum delta MTCI correlated quite closely with the time to maximum LDV output. The results indicate that both LDV and delta MTCI methods are valid, noninvasive assays for flushing reactions.
Ethanol↗
[Diagnostic value of various tuberculin preparations].
Despite declining incidence of tuberculosis in developed countries importance of tuberculin testing has not subsided. Previous investigations of the equivalence of 7 tuberculin preparations from 6 countries to RT 23 have shown differences in the diagnostic value of the tuberculin preparations. The smallest rates of negative skin-reactions in cases with bacteriologically confirmed tuberculosis were found with the hungarian tuberculin PPD-5 TU (HU 5 TU) and RT 23. The national tuberculin PPD Dessau 2 TU showed highest rates of non-reactors in tuberculous patients. In 400 cases of active bacteriologically confirmed tuberculosis further investigations were carried out to compare biologic equivalence of RT 23, HU 5 TU, tuberculin PPD Dessau 2 TU and the test-preparation PPD Dessau 5 TU with and without Tween addition and 7.5 TU without Tween. The results showed that with increase of antigen concentration to 5 TE or 7.5 TU the smaller reactions of 6 to 10 mm could be strengthened with a small, statistically not significant, increase of the mean value of reaction size but no increase of larger reactions of more than 20 mm. The rate of false negative reactions decreased using the test-preparation PPD 7.5 TU. The results allow to recommend the production of a national tuberculin preparation with higher antigen concentration biologically equivalent to RT 23 or HU 5 TU.
Germany, East↗
[Significance of search- and rapid reactions in syphilis serology].
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False Negative Reactions↗
[How to interpret the results of serological reactions for syphilis].
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False Negative Reactions↗
[Detection of anti-gonococcal antibodies using a dot immunobinding assay in a high risk female population].
The bacteriological diagnosis of gonorrhea in women has a low efficiency. A dot immunobinding assay, using whole piliated Neisseria gonorrhoeae cells, was used to detect antigonococcal antibodies in 300 prostitutes in whom a parallel Thayer-Martin culture of endocervical secretion was performed. Twenty sera from men with bacteriologically confirmed gonorrhoea were used as positive controls and 20 sera from children without history of gonococcal infections, as negative controls. Antibodies were detected in 49.7% of women and culture was positive in only one. All men with gonorrhea has positive titers and all sera from children were negative, except one that had a cross-reaction. Test sensitivity in the female population was 1 and specificity 0.5. There were no false negative reactions. Although the test detected antibodies in high risk women, there were cross-reactions. Therefore, the technique should be improved, using a more specific antigen.
Antibodies, Bacterial↗
Evaluation of a rapid fluorogenic method for the detection of Escherichia coli in dairy products.
A rapid fluorogenic medium was evaluated for the detection of Escherichia coli in dairy products. The medium was capable of detecting Esch. coli after 7.5 h incubation at 41.5 degrees C. Samples of pasteurized milk (136), raw milk (63), soft cheese (60) and pasteurized cream (39) were examined with media based on 4-methylumbelliferyl-beta-D-glucuronide (MUG-7) and Violet red bile agar and there were no significant differences between the numbers of Esch. coli detected on the two media. MUG-7 medium had a specificity of 98.6% and the small number of organisms giving a false positive reaction were identified as Klebsiella pneumoniae. The incidence of false negative results was approximately 2%. MUG-7 medium was suitable for pour plate, spread plate and membrane filtration methods. Possible applications of the method are discussed.
Animals↗
Antibody-dependent and direct lymphocyte-mediated cytotoxicity in patients on hemodialysis.
Twenty-two patients on chronic hemodialysis were tested for direct lymphocyte-mediated cytotoxicity (DCML) and antibody-dependent lymphocyte-mediated cytotoxicity (LALI) against selected panels of normal donor lymphocytes. The DCML reaction was only positive in patients who had received blood transfusions within the two or three months prior to testing. Thus this reaction has limited value in practice as a parameter for presensitization. The use of third-party effector cells and of target cells precoated with antibody in the LALI reaction was evaluated, and it is advocated that effector cells from the patient investigated and direct application of patient serum to reaction mixtures should be preferred in order to avoid false negative reactions. In patients who had once manifested lymphocytotoxins, LALI disclosed a much broader reactivity than seen with a conventional complement-dependent cytotoxicity technique (CDC), whereas in this study patients who had never developed cytotoxins were also negative with the LALI technique. It is concluded that a positive LALI cross-match, in spite of a negative CDC cross-match, will be a common finding in donor-recipient combinations where the recipient has preformed cytotoxins. The effect of this on subsequent graft prognosis needs further clarification.
Blood Transfusion↗
In vitro studies in nickel allergy: diagnostic value of a dual parameter analysis.
A comparison was made between the diagnostic value of assaying nickel-induced lymphocyte proliferation (lymphocyte transformation test, LTT) and migration inhibition factor (MIF) production in nickel contact sensitivity. Although lymphocyte proliferation was significantly increased in the group of patients with skin test reactivity to nickel, positive LTT were also frequently found in skin test-negative subjects: in 63% of subjects with and in 30% of subjects without a history of metal allergy. This would limit the value of the LTT as an in vitro correlate of skin test reactivity. However, in certain patients positive lymphocyte transformation may reveal nickel sensitization at a time of undetectable skin reactivity. Data obtained with the macrophage migration inhibition test (MMIT) showed a good correlation with nickel patch test reactions. Accurate determination of MIF became feasible by using cells from the human monocytoid cell line U937 as target cells in a microdroplet agarose assay. Using this MMIT, positive reactions occurred in 13% of the healthy controls and false-negative reactions were found in 26% of patients with positive skin test reactivity to nickel. As LTT and MMIT data appeared to be only weakly correlated in the individuals tested, a dual parameter analysis was performed. An excellent correlation [p = 1.8 (10(-8]] was found between skin test and in vitro reactivity for individuals with matching in vitro results (60% of all individuals tested). In those individuals with discordant in vitro data, skin testing will remain indispensable for diagnosing nickel allergy.
Cell Line↗
Radioimmunoassay for plasma histamine: a study of false positive and false negative values.
In order to achieve a correct diagnosis of drug anaphylaxis using a radioimmunoassay devoid of interferences, we have studied factors leading to false positive or false negative values of plasma histamine. Different steps in sample collection were studied systematically in 30 normal volunteers. False positive values were found in haemolysed samples, with histamine concentrations being correlated with haemoglobin concentrations, and where plasma was aspirated from the white-cell layer. There was no significant increase when a tourniquet or vacuum tubes were used, or when blood tubes were left at 4 degrees C overnight. In 12 patients who experienced an anaphylactic reaction, histamine disappeared from blood 10 times more slowly than expected. False negative values were found in two pregnant women and one heparinized patient. Histamine was remarkably stable in vitro in blood or plasma samples, whereas it disappeared rapidly when plasma from a pregnant woman or a heparinized patient was added to the sample. We conclude that false positive and false negative values are rare when using this radioimmunoassay.
Adolescent↗
Patch testing with a standard allergen ("screening") tray: rewards and risks.
The TRUE Test panels, which are the only patch testing devices approved by the Food and Drug Administration in the US, consist of 24 patches, one of which is a negative control. The remaining 23 patches contain 42 unique allergens and four complex mixtures. Although these panels contain approximately 1.4% of the > 3700 known allergens, they perform robustly in detecting allergic contact dermatitis (ACD). Twenty-eight percent of patients are fully evaluated by application of TRUE Test((R)). The present paper reviews the appropriate use of the TRUE Test panels. The need to determine relevance of any positive reaction is stressed. The common causes of false-positive and false-negative reactions are outlined. Those product types where the TRUE Test panels detect the majority of relevant allergic reactions are reviewed, as are the other sources of exposure to the allergens on these panels. The impact of ACD on quality of life is significant. Only by patch testing can the diagnosis be made.
Allergens↗
Studies in patients with corticosteroid contact allergy. Understanding cross-reactivity among different steroids.
BACKGROUND AND DESIGN: Most corticosteroid-allergic patients react to several corticosteroids. Irrefutable proof for the existence of cross-reactions is provided by reactions to substances to which the patient has never been exposed. Four groups of cross-reactions have been proposed, and our own observations support this. However, we have found that budesonide, in particular, tends to be involved not only in cross-reactions with corticosteroids of its own group (group B) but also with those of the ester group (group D). To test clinical observations on patients sensitive to corticosteroids and to establish a molecular basis for cross-reactivity patterns, a statistical analysis of our cases and a conformational study of major corticosteroids were performed. RESULTS: Statistically highly significant positive or negative correlations were found for the combination of tixocortol pivalate plus hydrocortisone and hydrocortisone plus budesonide, respectively. This indicates that budesonide and hydrocortisone or tixocortol pivalate detect different groups of corticosteroid-sensitive patients. Moreover, significant positive correlations were found between budesonide and amcinonide, both molecules belonging to the acetonide group C, and also between budesonide and some esters of group D such as hydrocortisone-17 butyrate and alclometasone dipropionate. These clinical observations were fully supported by a conformational analysis of the electronic shape of corticosteroids involved in this study. Groups A, B, and D were found to be highly homogeneous within each group in terms of molecular structures, while significant differences were observed among the groups. The special behavior of budesonide can be fully explained on the base of its unique molecular structure. Finally, molecular characteristics have been defined for each group. This could be useful for the prediction of potential cross-reactions to new corticosteroid molecules. CONCLUSIONS: The statistical analysis confirms that tixocortol pivalate and hydrocortisone contact allergies are definitely associated, while reactions to budesonide are strongly correlated with the reactions to both the acetonide group and the ester group. These clinical observations are fully supported by the conformational analysis of the molecules involved in this study. Tixocortol pivalate and budesonide should certainly be added to the standard series for the detection of patients sensitized to corticosteroids.
Adrenal Cortex Hormones↗
Detection of human immunodeficiency virus type 1 p24 antigen and plasma RNA: relevance to indeterminate serologic tests.
BACKGROUND: Most enzyme immunoassay-reactive specimens producing indeterminate Western blot results belong to individuals who are not infected with human immunodeficiency virus type 1 (HIV-1). However, a small percentage may correspond to early seroconversion or advanced disease, at which stage partial reactivity on Western blot may be observed. STUDY DESIGN AND METHODS: To determine the utility of HIV-1 p24 antigen and cell-free RNA detection for the resolution of Western blot-indeterminate serologic results, several types of enzyme immunoassay-positive, sero-indeterminate specimens were analyzed. Samples were obtained from infected individuals at the time of seroconversion (n = 20), from patients with AIDS (n = 2), as specimens from clinical samples obtained for diagnostic testing (n = 57), from blood donors producing persistent indeterminate results (n = 47), and from random blood donors (n = 72). RESULTS: HIV-1 p24 antigen was detected in 10 of 20 specimens collected from 9 of 12 individuals who seroconverted and in 2 of 2 AIDS patients. HIV-1 plasma RNA was positive in 22 of 22 samples from those 14 individuals. All of 57 diagnostic specimens and 47 samples obtained from persistently indeterminate donors were negative for HIV-1 p24 antigen and plasma HIV-1 RNA. One of 72 blood donor specimens was positive for HIV-1 plasma RNA and had borderline reactivity for p24 antigen. CONCLUSION: The detection of plasma RNA appears to be sensitive and specific; negative test results may be used to identify false-positive serologic reactions. The detection of p24 antigen and plasma RNA can also be used to confirm HIV-1 infection in persons with indeterminate serologic results associated with early seroconversion or late-stage disease.
Blotting, Western↗
Detection of gram-negative bacteria in urine by the chromogenic limulus assay.
The value of the chromogenic limulus assay for detection of gram-negative bacteria in urine was determined. The assay was performed in microtiter plates at room temperature. In 311 consecutively collected urine samples from patients with suspected urinary tract infection, the assay was positive in all 35 samples containing greater than or equal to 10(5) bacteria/ml. No false positive or false negative results were obtained. Four of six urine specimens from patients with gonococcal infection were positive in the assay, whereas samples from patients with chlamydial infection did not yield a positive result. The assay is a rapid and reliable method for detection of urinary tract infection caused by gram-negative bacteria when greater than or equal to 10(5) bacteria/ml are present.
Bacteriuria↗
Evaluation of a non-radioactive DNA probe for confirmatory identification of Neisseria gonorrhoeae.
A biotinylated DNA probe combined with a streptavidin-peroxidase complex for the identification of culture isolates of N. gonorrhoeae (Ortho diagnostic systems, Neckargemünd, FRG) was compared with the conventional carbohydrate utilisation test as reference. All 118 strains identified by the reference method as N. gonorrhoeae also gave positive reactions with the DNA hybridisation assay. However, with this test 2 of 23 non-gonococcal Neisseria or Branhamella species were identified as N. gonorrhoeae as well. The study shows that the DNA hybridisation technique can principally be used for the confirmatory identification of N. gonorrhoeae, but since specificity is particularly essential for confirmatory identification, the DNA hybridisation assay evaluated cannot be recommended for routine diagnosis.
Carbohydrate Metabolism↗
Detection kinetics for positive blood culture bottles by using the VITAL automated system.
The VITAL system principle is based on homogeneous fluorescence technology. During an 11-month period, a total of 19,706 blood cultures from adult patients hospitalized in various establishments of the Montpellier Teaching Hospital were collected in VITAL bottles, of which 1,939 were declared positive. Only 204 bottles (1.04%) were false positives. The 1,735 true-positive bottles were collected from 130 patients. The final visual control permitted the detection of 10 falsely negative bottles (0.05%), of which 5 contained clinically significant microorganisms from four patients. The kinetics of detection for all microorganisms showed that 66.6% were detected within 24 h, 83.1% within 48 h, 95.5% within 120 h, and 100% within 150 h. No clinical episode would have been missed had a 5-day protocol been used instead of a 7-day protocol. Among the positive bottles, 65.7% were detected by the SLOPE algorithm, 20.1% by the DELTA algorithm, and 14.2% by the THRESHOLD algorithm. This retrospective study of our results shows that a 5-day protocol is sufficient for the detection of septic episodes using the VITAL system.
Adult↗