Preventing False Negatives for Histochemical Detection of Phenolics and Lignins in PEG-Embedded Plant Tissues

Polyethylene glycol (PEG) is a low-cost and advantageous embedding medium, which maintains the majority of cell contents unaltered during the embedding process. Some hard or complex plant materials are better embedded in PEG than in other usual embedding media. However, the histochemical tests for phenolics and lignins in PEG-embedded plant tissues commonly result in false negatives. We hypothesize that these false negatives should be prevented by the use of distinct fixatives, which should avoid the bonds between PEG and phenols. Novel protocols for phenolics and flavanols detection are efficiently tested, with fixation of the samples in ferrous sulfate and formalin or in caffeine and sodium benzoate, respectively. The differentiation of lignin types is possible in safranin-stained sections observed under fluorescence. The Maule’s test faultlessly distinguishes syringyl-rich from guaiacyl- and hydroxyphenyl-rich lignins in PEG-embedded material under light microscopy. Current hypothesis is corroborated, that is, the adequate fixation solves the false-negative results, and the new proposed protocols fill up some gaps on the detection of phenolics and lignins.

Download Full-text

A Rapid and Low-Cost protocol for the detection of B.1.1.7 lineage of SARS-CoV-2 by using SYBR Green-Based RT-qPCR

10.1101/2021.01.27.21250048 ◽

2021 ◽

Author(s):

Fadi Abdel Sater ◽

Mahmoud Younes ◽

Hassan Nassar ◽

Paul Nguewa ◽

Kassem Hamze

Keyword(s):

Low Cost ◽

False Negative ◽

Sybr Green ◽

Reproductive Number ◽

Rt Pcr ◽

Negative Results ◽

False Negative Results ◽

New Variant ◽

Primer Sets ◽

The Uk

AbstractBackgroundThe new SARS-CoV-2 variant VUI (202012/01), identified recently in the United Kingdom (UK), exhibits a higher transmissibility rate compared to other variants, and a reproductive number 0.4 higher. In the UK, scientists were able to identify the increase of this new variant through the rise of false negative results for the spike (S) target using a three-target RT-PCR assay (TaqPath kit).MethodsTo control and study the current coronavirus pandemic, it is important to develop a rapid and low-cost molecular test to identify the aforementioned variant. In this work, we designed primer sets specific to SARS-CoV-2 variant VUI (202012/01) to be used by SYBR Green-based RT-PCR. These primers were specifically designed to confirm the deletion mutations Δ69/Δ70 in the spike and the Δ106/Δ107/Δ108 in the NSP6 gene. We studied 20 samples from positive patients, 16 samples displayed an S-negative profile (negative for S target and positive for N and ORF1ab targets) and four samples with S, N and ORF1ab positive profile.ResultsOur results emphasized that all S-negative samples harbored the mutations Δ69/Δ70 and Δ106/Δ107/Δ108. This protocol could be used as a second test to confirm the diagnosis in patients who were already positive to COVID-19 but showed false negative results for S-gene.ConclusionsThis technique may allow to identify patients carrying the VUI (202012/01) variant or a closely related variant, in case of shortage in sequencing.

Download Full-text

Phenothiazine Derivatives in Urine: "False Nagative Results" With the Forrest Color Test (FPN), and a Method for Their Elimination

Clinical Chemistry ◽

10.1093/clinchem/11.10.914 ◽

1965 ◽

Vol 11 (10) ◽

pp. 914-919

Author(s):

K N Campbell

Keyword(s):

False Negative ◽

False Positives ◽

Phenothiazine Derivatives ◽

Color Test ◽

False Negatives ◽

Delayed Reaction ◽

Negative Results ◽

False Negative Results ◽

Phenothiazine Drugs ◽

Urine Specimens

Abstract More than 100 Forrest color tests (FPN) were performed on urine specimens from patients taking phenothiazine drugs. The results obtained showed > 20% "false negatives" and 6% "false positives." A delayed reaction due to possible individual patient variation seems to have been the cause for false-negative results. These false negatives were shown to disappear when test readings were delayed for 1-5 min. Some false positives were due to liver dysfunction.

Download Full-text

Onychomycosis Infections

Journal of the American Podiatric Medical Association ◽

10.7547/15-136 ◽

2017 ◽

Vol 107 (4) ◽

pp. 280-286 ◽

Cited By ~ 11

Author(s):

Aditya K. Gupta ◽

Kerry-Ann Nakrieko

Keyword(s):

False Negative ◽

Kappa Statistic ◽

False Negatives ◽

Negative Results ◽

False Negative Results ◽

Repeated Sampling ◽

Polymerase Chain ◽

Serial Samples ◽

Repeated Samples ◽

Infecting Organisms

Background: Mycological culture is the traditional method for identifying infecting agents of onychomycosis despite high false-negative results, slower processing, and complications surrounding nondermatophyte mold (NDM) infections. Molecular polymerase chain reaction (PCR) methods are faster and suited for ascertaining NDM infections. Methods: To measure agreement between culture and PCR methods for identification of infecting species of suspected onychomycosis, single toenail samples from 167 patients and repeated serial samples from 43 patients with suspected onychomycosis were processed by culture and PCR for identification of 16 dermatophytes and five NDMs. Agreement between methods was quantified using the kappa statistic (κ). Results: The methods exhibited fair agreement for the identification of all infecting organisms (single samples: κ = 0.32; repeated samples: κ = 0.38). For dermatophytes, agreement was moderate (single samples: κ = 0.44; repeated samples: κ = 0.42). For NDMs, agreement was poor with single samples (κ = 0.16) but fair with repeated samples (κ = 0.25). Excluding false-negative reports from analyses improved agreement between methods in all cases except the identification of NDMs from single samples. Conclusions: Culture was three or four times more likely to report a false-negative result compared with PCR. The increased agreement between methods observed by excluding false-negative reports statistically clarifies and highlights the major discord caused by false-negative cultures. The increased agreement of NDM identification from poor to fair with repeated sampling along with their poor agreement in the single samples, with and without false-negatives, affirms the complications of NDM identification and supports the recommendation that serial samples help confirm the diagnosis of NDM infections.

Download Full-text

FALSE-NEGATIVE RESULTS IN SCREENING PROGRAMS

International Journal of Technology Assessment in Health Care ◽

10.1017/s0266462300105021 ◽

2001 ◽

Vol 17 (2) ◽

pp. 164-170 ◽

Cited By ~ 11

Author(s):

Mark Petticrew ◽

Amanda Sowden ◽

Deborah Lister-Sharp

Keyword(s):

Negative Impact ◽

Relevant Literature ◽

False Negative ◽

Quantitative Information ◽

Public Confidence ◽

Psychological Consequences ◽

False Negatives ◽

Screening Programs ◽

Negative Results ◽

False Negative Results

Objectives: Assessment of the appropriateness of screening programs involves consideration of the harms as well as the benefits. These harms include the risk of false-negative results, the consequences of which have remained underinvestigated. This paper reports the results of a systematic literature review that aimed to assess the medical psychological, economic, and legal consequences of false-negative results in national screening programs.Methods: The review included a comprehensive literature search and contact with experts to identify relevant literature. Most studies that were identified presented only anecdotal evidence. However, thirteen studies presented quantitative information on medical consequences of false negatives, eight studies presented information on psychological consequences, and two studies presented information on economic consequences.Results: The strength of evidence from most of the primary studies was low. There is some evidence, however, that false-negative results may have a large legal impact. There is also a consensus in the literature that false negatives may have a negative impact on public confidence on screening; evidence is however limited.Conclusions: False negatives are evident even in high-quality screening programs. They may have the potential to delay the detection of breast and cervical cancer, but there is little evidence to help in assessing their psychological consequences. They also may lead to legal action being taken by those affected and may reduce public confidence in screening. Their impact may be reduced by provision of full information to participants about the benefits and limitations of screening programs and by increasing public education on these issues.

Download Full-text

Analysis and Prediction of COVID-19 Patients’ False Negative Results for SARS-CoV-2 Detection with Pharyngeal Swab Specimen: A Retrospective Study

10.1101/2020.03.26.20043042 ◽

2020 ◽

Cited By ~ 4

Author(s):

Hui Xu ◽

Li Yan ◽

Chun (Martin) Qiu ◽

Bo Jiao ◽

Yanyan Chen ◽

...

Keyword(s):

Nucleic Acid ◽

Time Window ◽

Clinical Symptoms ◽

False Negative ◽

Ct Imaging ◽

Nucleic Acid Detection ◽

False Negatives ◽

Negative Results ◽

False Negative Results ◽

Blood Routine

ABSTRACTBackgroundFalse negative results of SARS-CoV-2 nucleic acid detection pose threats to COVID-19 patients and medical workers alike.ObjectiveTo develop multivariate models to determine clinical characteristics that contribute to false negative results of SARS-CoV-2 nucleic acid detection, and use them to predict false negative results as well as time windows for testing positive.DesignRetrospective Cohort Study (Ethics number of Tongji Hospital: No. IRBID: TJ-20200320)SettingA database of outpatients in Tongji Hospital (University Hospital) from 15 January 2020 to 19 February 2020.Patients1,324 outpatients with COVID-19MeasurementsClinical information on CT imaging reports, blood routine tests, and clinic symptoms were collected. A multivariate logistic regression was used to explain and predict false negative testing results of SARS-CoV-2 detection. A multivariate accelerated failure model was used to analyze and predict delayed time windows for testing positive.ResultsOf the 1,324 outpatients who diagnosed of COVID-19, 633 patients tested positive in their first SARS-CoV-2 nucleic acid test (47.8%), with a mean age of 51 years (SD=14.9); the rest, which had a mean age of 47 years (SD=15.4), tested negative in the first test. “Ground glass opacity” in a CT imaging report was associated with a lower chance of false negatives (aOR, 0.56), and reduced the length of time window for testing positive by 26%. “Consolidation” was associated with a higher chance of false negatives (aOR, 1.57), and extended the length of time window for testing positive by 44%. In blood routine tests, basophils (aOR, 1.28) and eosinophils (aOR, 1.29) were associated with a higher chance of false negatives, and were found to extend the time window for testing positive by 23% and 41%, respectively. Age and gender also affected the significantly.LimitationData were generated in a large single-center study.ConclusionTesting outcome and positive window of SARS-CoV-2 detection for COVID-19 patients were associated with CT imaging results, blood routine tests, and clinical symptoms. Taking into account relevant information in CT imaging reports, blood routine tests, and clinical symptoms helped reduce a false negative testing outcome. The predictive AFT model, what we believe to be one of the first statistical models for predicting time window of SARS-CoV-2 detection, could help clinicians improve the accuracy and efficiency of the diagnosis, and hence, optimizes the timing of nucleic acid detection and alleviates the shortage of nucleic acid detection kits around the world.Primary Funding SourceNone.

Download Full-text

Role and limits of testicular phleboscintigraphy in the diagnostic evaluation of varicocele

Urologia Journal ◽

10.1177/039156039406100202 ◽

1994 ◽

Vol 61 (2) ◽

pp. 98-102

Author(s):

A. Raimoldi ◽

G.L. Berti ◽

V. Giola ◽

G.L. Leidi ◽

A. Maccaroni ◽

...

Keyword(s):

Doppler Ultrasonography ◽

Low Cost ◽

False Negative ◽

High Sensitivity ◽

Diagnostic Evaluation ◽

Ultrasound Technique ◽

Negative Results ◽

False Negative Results ◽

First Choice ◽

Choice Method

The Authors wanted to check the reliability of testicular phleboscintigraphy in the diagnostic evaluation of varicocele, comparing it to Doppler ultrasonography. To this end, 98 patients affected by clinically evident left idiopathic varicocele were tested. The two methods gave equivalent results in all patients affected by 2nd and 3rd clinical degree varicocele, while testicular phleboscintigraphy gave false negative results in 7 patients with 1st degree varicocele, due to renospermatic retrograde flow. Therefore, in the Authors' opinion, the Doppler ultrasound technique can be considered as a first choice method in the study of varicocele, thanks to its high sensitivity associated with low cost, whereas testicular phleboscintigraphy can be used either when Doppler ultrasonography evaluation is not reliable or as a second examination to confirm the Doppler results, especially in patients with 2nd and 3rd clinical degree varicocele.

Download Full-text

Elimination of False Negative Results with the FPN Forrest Test for Phenothiazine Derivatives in Urine

Clinical Chemistry ◽

10.1093/clinchem/12.6.379 ◽

1966 ◽

Vol 12 (6) ◽

pp. 379-384 ◽

Cited By ~ 6

Author(s):

Irene S Forrest ◽

Fred M Forrest ◽

Saul L Kanter

Keyword(s):

Reading Time ◽

False Negative ◽

False Positives ◽

Phenothiazine Derivatives ◽

False Negatives ◽

Negative Results ◽

Color Development ◽

False Negative Results ◽

Color Reactions ◽

Urine Specimens

Abstract With the FPN Forrest test for urinary phenothiazine derivatives, omission of drug intake was found to be the most frequent cause of negative color reactions; accordingly, these negative reactions are true negatives. Excessive dilution of urine specimens occasionally yielded "apparent false negatives" by producing traces of drug metabolites, which cannot be detected without modification of the test. When measures to eliminate these conditions are taken, the previously specified reading time (10 sec. after mixing urine and reagent) is reliable. Unspecific color development due to reaction between endogenous urinary constituents and reagent appeared with a delay of 30 sec. or more, and hence recent recommendations of delaying reading times for the test were found to be unsuitable and productive of false positives.

Download Full-text

Detection of Phenothiazine Derivatives in Urine

Clinical Chemistry ◽

10.1093/clinchem/12.12.844 ◽

1966 ◽

Vol 12 (12) ◽

pp. 844-848 ◽

Cited By ~ 2

Author(s):

Herman Brownstein ◽

Alfred R Roberge

Keyword(s):

False Negative ◽

Control Group ◽

Phenothiazine Derivatives ◽

False Negatives ◽

Negative Results ◽

False Negative Results ◽

Positive Results ◽

Urine Specimens ◽

Modified Test

Abstract Findings of the present study agree with published results that showed an incidence of approximately 25% "false negative" results with the Forrest FPN test for phenothiazine derivatives in urine. A recently published modification purportedly decreased these "false negatives" to less than 5%. However, our control group of negative urine specimens omitted in Campbell's study, yielded 100% negative results with the FPN test and 81% positive results with the modified test. Phenistix (Ames) was evaluated for elimination of false negative readings but was found not to have any advantage for this purpose. Data are also presented indicating differing sensitivities of the Forrest FPN test to various phenothiazine derivatives.

Download Full-text

In silico evaluation of the impact of the Omicron variant on the sensitivity of RT-qPCR assays for SARS-CoV-2 detection using whole genome sequencing

10.21203/rs.3.rs-1220446/v1 ◽

2022 ◽

Author(s):

Divya Sharma ◽

Chengjin Ye ◽

Giusppe Lippi ◽

Jordi B. Torrelles ◽

Luis Martinez-Sobrido ◽

...

Keyword(s):

In Silico ◽

False Negative ◽

Whole Genome ◽

False Negatives ◽

Negative Results ◽

False Negative Results ◽

The World ◽

Reverse Primer ◽

Primer Annealing ◽

The Impact

Abstract Background The novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variant of concern (VoC) Omicron (B.1.1.529) has rapidly spread around the world presenting a new threat to global public human health. Due to the large number of mutations possessed by Omicron, concerns have emerged over potentially reduced diagnostic accuracy of reverse transcription polymerase chain reaction (RT-qPCR), the gold standard diagnostic test for SARS-CoV-2. Here, we aimed to assess the impact of Omicron on the integrity and sensitivity of RT-qPCR assays used for coronavirus disease-2019 (COVID-19) diagnosis via in silico analysis employing whole genome sequencing data and evaluated the potential for false negatives or test failure due to mismatches between primers/probes and viral genome. Methods In silico sensitivity of 12 RT-qPCR tests (containing 30 primers and probe sets) developed for detection of SARS-CoV-2 reported by the World Health Organization (WHO) or available in the literature, was assessed for use in detecting SARS-CoV-2 Omicron BA.1 and BA.2 sublineages, obtained after removing redundancy from publicly available genomes from National Center for Biotechnology Information (NCBI) and Global Initiative on Sharing Avian Influenza Data (GISAID) databases. The mismatches between the amplicon regions of the SARS-CoV-2 Omicron VoC and primers and probe sets were evaluated, and the clustering analysis of the corresponding amplicon sequences was carried out. Results From the 232 representative SARS-CoV-2 BA.1 Omicron sublineage genomes analyzed, 229 showed substitutions at the forward primer annealing site for assay China-CDC N, 226 showed mismatches in the reverse primer annealing site for assay Thai N, and all 232 had substitution at the 3’ end of the reverse primer annealing site for assay HKUniv RdRp/Hel. Therefore, the lowest sensitivity was observed for assay ChinaCDC N, Thai N and HKUniv RdRp/Hel for SARS-CoV-2 BA.1 sublineage genomes. For 5 SARS-CoV-2 BA.2 Omicron sublineage genomes, false negative results were observed for assays ChinaCDC N, Thai N, HKUniv RdRp/Hel, SigmAldr S5, SigmAldr S6 and HKUniv S. Conclusion In this study, we observed three (25%) assays (ChinaCDC N, Thai N, and HKUniv RdRp/Hel) demonstrated potential for false negatives for the SARS-CoV-2 Omicron BA.1 sublineage, while four (33.3%) assays (ChinaCDC N, Thai N, HKUniv RdRp/Hel, HKUniv S, SigmAldr S5 and SigmAldr S6) demonstrated potential false negative results for the for SARS-CoV-2 Omicron BA.2 sublineage, which also has the potential for Spike (S) gene dropout despite lacking 69-70 deletion in the S gene. Further, amplicon clustering and additional substitutions analysis along with the sensitivity analysis could be used for modification and development of RT-qPCR assays for detection of SARS-CoV-2 Omicron VoC lineages.

Download Full-text

Detection of Naegleria spp. and Naegleria fowleri: a comparison of flagellation tests, ELISA and PCR

Water Science & Technology ◽

10.2166/wst.2003.0177 ◽

2003 ◽

Vol 47 (3) ◽

pp. 117-122 ◽

Cited By ~ 17

Author(s):

J. Behets ◽

F. Seghi ◽

P. Declerck ◽

L. Verelst ◽

L. Duvivier ◽

...

Keyword(s):

Power Plants ◽

False Negative ◽

Naegleria Fowleri ◽

False Negatives ◽

Heterogeneous Distribution ◽

Negative Results ◽

Specific Pcr ◽

False Negative Results ◽

Nægleria Fowleri ◽

Amoebic Meningoencephalitis

To detect Naegleria spp, in particular Naegleria fowleri, the causative agent of human primary amoebic meningoencephalitis, a flagellation test (FT) is routinely used followed by a specific ELISA. A positive FT indicates the presence of Naegleria spp although some false negatives are likely to occur since parameters for enflagellation vary greatly. As negative FTs are not routinely screened any further for the presence of N. fowleri, this could result in an underestimation of the presence of this pathogen. Therefore, amoebae were further analysed using ELISA and standard PCR not only after a positive but also after a negative FT. In this study 39 cultures containing amoebae were tested with FT, ELISA and the two PCR assays with 11 positive for FT. These were submitted to ELISA and four confirmed as N. fowleri. PCR with the common primer-set on these 11 positive FTs revealed all as Naegleria spp. The specific PCR used on these cultures detected four positive for N. fowleri, corresponding totally with the ELISA results. The 28 negative flagellation tests were also submitted to ELISA and PCR. Of these, 11 were identified as Naegleria spp with common PCR and six as N. fowleri as well as with ELISA and the specific PCR. When the detection of Naegleria spp is based on intermediary processes, such as flagellation tests, false negatives are likely to occur leading to severe underestimations. This study has shown that amoebae taken from negative FTs can be identified as Naegleria spp and N. fowleri when using PCR and ELISA. The application of at least one of the specific N. fowleri tests is recommended for routine screening. The heterogeneous distribution of the false negative results between the different power plants suggested the presence of different genotypes.

Download Full-text