Cause Of False Positives Research Articles

The Maximum Standardized Uptake Values on Integrated FDG-PET/CT Is Useful in Differentiating Benign From Malignant Pulmonary Nodules

Positron emission tomography (PET) is often used for an indeterminate pulmonary nodule. This is a prospective study on a consecutive series of patients who had an indeterminate pulmonary nodule that was 2.5 cm or less, underwent integrated positron emission tomography using fluorodeoxyglucose-PET/computed tomographic [FDG-PET/CT] scan with the maximum standardized uptake values (maxSUVs) reported, and who underwent complete resection. There were 585 patients (401 men). A total of 496 patients had a malignant nodule and the median maxSUV was 8.5 (range, 0 to 36). Eighty-nine patients had a benign nodule and the median maxSUV was 4.9 (range, 0 to 28, p < 0.001). If the maxSUV was between 0 and 2.5 there was a 24% chance the nodule was malignant, if between 2.6 and 4.0 it was 80%, and if 4.1 or greater it was 96%. False negative FDG-PET/CT was from bronchoalveolar carcinoma in 11 patients, carcinoid in 4, and renal cell in 2. False positives included fungal infections in 16 patients. Nodal involvement, whether malignant or infectious, was more likely with a pulmonary mass that had a higher maxSUV (8.4 vs 3.8 for nonmalignant lesions, 9.8 vs 4.5 for malignant lesions). Although integrated FDG-PET/CT is a valuable study for an indeterminate pulmonary nodule, one must be aware of causes of false positives and negatives. There is a 24% chance a suspicious nodule that has a maxSUV of 0 to 2.5 is cancer. The higher the maxSUV of the primary mass the more likely the nodes are to be involved with either malignancy or infection, and this may help direct nodal biopsy instead of pulmonary resection.

Automated mass detection in contrast-enhanced CT colonography: an approach based on contrast and volume

The purpose of this feasibility study was to design and test an algorithm for automating mass detection in contrast-enhanced CT colonography (CTC). Five patients with known colorectal masses underwent a pre-surgical contrast-enhanced (120 ml volume 1.6 g iodine/s injection rate, 60 s scan delay) CTC in high spatial resolution (16-slice CT: collimation: 16x0.75 mm, tablefeed: 24 mm/0.5 s, reconstruction increment: 0.5 mm). A CT-density- and volume-based algorithm searched for masses in the colonic wall, which was extracted before by segmenting and dilating the colonic air lumen and subtracting the inner air. A radiologist analyzed the detections and causes of false positives. All masses were detected, and false positives were easy to identify. Combining CT density with volume as a cut-off is a promising approach for automating mass detection that should be further refined and also tested in contrast-enhanced MR colonography. More information under http://www.screening.info.

Electrocardiogram during tachycardia in patients with anterograde conduction over a Mahaim fiber: Old criteria revisited

The aim of this study was to prospectively evaluate the sensitivity, specificity, and positive and negative predictive values of previously described ECG criteria to identify preexcited tachycardia due to decrementally conducting accessory pathways (QRS axis between 0 and -75 degrees , QRS width < or = 0.15 seconds, an R wave in lead I, an rS pattern in lead V(1), RS > 1 QRS transition > V(4), and cycle length between 220 and 450 ms). Preexcited tachycardia associated with decrementally conducting right-sided accessory pathways usually shows a rather "narrow" QRS complex and can be difficult to differentiate from supraventricular tachycardia (SVT) with left bundle branch block (LBBB) aberrant conduction. We analyzed three groups of patients: 32 patients with an atriofascicular pathway (group I); 8 patients with long (n = 3) or short (n = 5) decrementally conducting right-sided AV pathway (group II); and a control group that consisted of 35 patients with SVT and LBBB (group III). Presence of all six criteria had 87.5% sensitivity in group I and a 0% sensitivity in group II. There were four false negatives in group I. The negative predictive value was 82.5%, with six false positives in group III (five patients with an aberrant LBBB-shaped tachycardia with ventriculoatrial conduction over an accessory AV pathway). The criterion cycle length was not helpful. Criteria for identifying a tachycardia with anterograde conduction over a Mahaim fiber are helpful only in atriofascicular pathways, with a sensitivity of 87.5% and a negative predictive value of 82.5%. The major cause of false positives was a tachycardia with aberrant LBBB conduction and ventriculoatrial conduction over an accessory AV pathway.

Identification of nontuberculous mycobacteria existing in tap water by PCR-restriction fragment length polymorphism.

This paper presents the finding of the possible cause of the high false-positive rate in acid-fast staining in histological examinations. Using acid-fast staining, culture, and PCR, acid-fast bacilli were detected in 83.7% of 49 hospital tap water samples and nontuberculous mycobacteria (NTM) were detected in 20.4% of the same 49 samples. The 10 NTM isolates were also identified to the species level using PCR-restriction fragment length polymorphism. Our findings indicate that NTM in hospital tap water are the possible cause of false positives in acid-fast staining and of nosocomial infection in immunocompromised patients.

Strategy linking several analytical methods of neonatal screening for sickle cell disease.

The French national programme for the neonatal screening of sickle cell disease (SCD) was set up in 1995. This screening is targeted at newborn infants at risk. Over 5 years, 115,480 newborn infants were tested from 80 maternity departments from the northern part of the Paris area. 250 Patients with SCD were identified--that is, one in 462 newborn infants tested. Carriers for a haemoglobin (Hb) variant are frequent (5.34%). Some uncommon Hb variants were also identified, which gave rise to pitfalls to the testing when associated with HbS: HbKorle-Bu, HbHope, HbBougardirey-Mali, and HbLadésirade (4% of SS-like profiles). An effective screening strategy was developed to avoid these false positive and false negative responses. Isoelectric focusing (IEF), the method of primary screening, is rapid and inexpensive. Cation exchange high performance liquid chromatography (CE-HPLC), which is automated, fast, and quantitative was selected as a secondary method. IEF diagnosed normal profiles in 89% of the tested samples from newborn infants. CE-HPLC identified most of the common Hb variants by their retention time and the measure of HbA/HbS ratio, important for the differential diagnosis between an asymptomatic HbS carrier and an HbS/beta+thal compound heterozygote. Furthermore, the high sensitivity of the CE-HPLC detected as little as 0.5% of a Hb variant. This avoided false negatives in samples from premature or transfused newborn infants. All samples with SS-like profiles were confirmed with a second CE-HPLC with another programme. A combination of these three methods confirmed the status of 99.7% of the samples from the tested newborn infants. Some cases required a reverse phase-HPLC method (for gamma-globin or alpha-globin chain variants). Finally, some exceptional samples required confirmation by testing DNA extracted with Güthrie paper for a precise diagnosis. This effective strategy combining several methods dramatically reduces the risk of errors. Many families are thus spared unnecessary worrying recalls. The only unavoidable cause of false positives remains the HbS/hereditary fetal Hb (HPFH).

A Model of Elegance

GenBank, http://www.ncbi.nlm.nih.gov/Web/GenbankGenome Sequencing Center, University of Washington School of Medicine, http://genome.wustl.edu/gsc/gschmpg.htmlThe Sanger Center, http://www.sanger.ac.ukXREFdb, http://www.ncbi.nlm.nih.gov/Bassett/modelorgs

The effect of diffusion on the immunolocalization of antigen.

Diffusion prior to tissue fixation may result in immunohistochemical localization of antigen at sites in which it does not occur in vivo. The extent and speed with which this may occur have been investigated with several antigens of different molecular weights in tissues which were left unfixed for various lengths of time. There was clear evidence of diffusion when fixation was delayed for as little as 1 h, resulting in focal labelling of cells which did not contain antigen in rapidly fixed tissues. Falsely localized antigen was particularly evident adjacent to sites containing high antigen concentrations and might be expected in areas permeated by antigen-containing tissue fluid. These findings substantiate the view that diffusion of antigen should be considered as a cause of false positivity in any immunolocalization study.

Dépistage de la maladie de Chagas par immunoenzymologie: Comparaison de l'ELISA avec l'immunofluorescence et l'hémagglutination indirecte chez 976 donneurs de sang

The efficiency of an immunoenzymatic technique (ELISA) for the systematic research of Chagas' disease in blood donors was compared with one of 2 well-known methods, indirect haemagglutination (IHA) and indirect fluoro immuno assay (IFA). For the ELISA technique two different antigenic extracts from epimastigote culture forms of T. cruzi, were used for sensitizing the polystyrene plates: a crude extract (Ag R) and a delipidized one (Ag B). Firstly the authors tested these 3 techniques in 5 control groups: sera from Chagas' disease, negative control sera, sera from visceral leishmaniasis, african trypanosomiasis and finally monoclonal gammapathies, the high levels of blood proteins being a possible cause of false positives. Secondly the screening of Chagas' disease was performed in the same way in 976 blood donors from Recife, Brazil. In the case of the Ag-R extract used in the ELISA technique a high cross-reactivity was found with visceral leishmaniasis sera, along a risk of false positives with gammapathic ones. The sensitivity of this technique was found to be high (3,3 +/- 1 p. cent of positive blood donors) and a very good correlation was found with the reference techniques, IFA and IHA, the sensitivity of which is lower (2,3 +/- 1 and 1,7 +/- p. cent). The use of a delipidized antigenic extract (Ag B) for the ELISA technique is not suitable, in spite of an apparent higher specificity: indeed, the positives rate is high (11,5 +/- 0,2 p. cent), but the correlation is very weak or non existent in the case of IHA or IFA. In conclusion, the ELISA technique using a crude extract of T. cruzi appears to be a very convenient method for screening blood donors with Chagas' disease, the lack of specificity due to leishmaniasis or monoclonal blood proteins not posing any real problem to blood banking.

Value of the Kahn test in Africans.

Originally it was believed that the various standard tests were specific for syphilis, and that the finding of a positive test was proof that the patient had syphilis. The fact that the tests could be undertaken with a non-specific antigen extracted from beef-heart, raised doubts as to the specificity of the tests. It subsequently became apparent that positive results were sometimes obtained from patients other than syphilitics, and, with the passing of years, more and more causes of false positives have been reported, together with reports of false positives for which no cause could be ascribed, so that now there is a formidable literature on the subject. The British Journal of Venereal Diseases (1951), in an editorial devoted to the subject, suggested that the increasing awareness of the problem of the BFP could be ascribed to two causes: