scholarly journals Evaluation of indeterminate SARS-CoV-2 results with repeat testing on an alternative platform

2021 ◽  
Vol 156 (Supplement_1) ◽  
pp. S133-S134
Author(s):  
T Lynn ◽  
R M Martinez
Keyword(s):  
False Positive ◽  
Limit Of Detection ◽  
False Negative ◽  
Past Infection ◽  
Repeat Testing ◽  
Negative Results ◽  
Target Analytes ◽  
Previous Infection ◽  
Clinical Accuracy ◽  
Positive Results

Abstract Introduction/Objective Accurate SARS-CoV-2 results are crucial for patient management and infection prevention. Result confidence decreases with low viral load because near the assay’s limit of detection (LOD), test results may alternate between positive and negative, as characterized by Poisson distribution for target analytes at low density. Low positive results may indicate past infection, early infection, a vaccinated individual with low level viral shed, or a false-positive result. EUA methods provide guidance on test interpretation, but laboratories should assess clinical accuracy. The purpose of this study was to assess clinical accuracy of specimens with low positive results. Methods/Case Report Respiratory specimens were tested by Cepheid Xpert® Xpress SARS-CoV-2 assay with positive results up to a Ct of 45. A low positive (defined as Ct ≥35), which could not be confirmed by Hologic Aptima® SARS-CoV-2 assay was reported as indeterminate and repeat testing recommended. Repeat testing occurred by Cepheid, Hologic, BioFire, Roche, or Quest assays. Retrospectively, final results were extracted from the LIS (Epic Beaker, Madison, WI, version May 2020) for 5-months (12/1/2020 to 5/31/2021), and chart review performed. Results (if a Case Study enter NA) A total of 19,969 tests were performed; 10.4% (n=2,083) were positive, 89% (n=17,728) negative, and 0.79% (n=158) indeterminate. Previous infection (up to 3 months prior) was documented in 18% (n=28) of indeterminate results and defined as true positive. Of remaining indeterminate results, 43% (n=68) had repeat testing as recommended by laboratory; 26% (n=18) were positive and 74% (n=50) were negative. The average number of days between indeterminate and negative result was 7.25 (range 1-38). Conclusion Result discordance occurred in < 1% of all samples, excellent agreement. For low positive samples, discordance was higher, as expected. It’s impossible to determine if negative results from the 50 repeat samples were false-positive by Cepheid or false-negative by other methods. In summary, 32% (50/158) of indeterminant samples did not repeat as positive. Overall concordance was high and results fluctuate when low virus is present. In absence of symptoms, we conclude repeat testing is not routinely recommended. Laboratories must recognize that normal variability occurs near assay LOD and must critically assess performance against other methods with similar LODs to fully assess performance of EUA methods.

Critical Evaluation of Impedance Phlebography for the Diagnosis of Deep Vein Thrombosis

1974 ◽  
Vol 31 (02) ◽  
pp. 273-278
Author(s):  
Kenneth K Wu ◽  
John C Hoak ◽  
Robert W Barnes ◽  
Stuart L Frankel
Keyword(s):  
Deep Vein Thrombosis ◽  
False Positive ◽  
False Negative ◽  
Critical Evaluation ◽  
Original Method ◽  
Vein Thrombosis ◽  
Negative Results ◽  
False Negative Results ◽  
Deep Vein ◽  
Positive Results

SummaryIn order to evaluate its daily variability and reliability, impedance phlebography was performed daily or on alternate days on 61 patients with deep vein thrombosis, of whom 47 also had 125I-fibrinogen uptake tests and 22 had radiographic venography. The results showed that impedance phlebography was highly variable and poorly reliable. False positive results were noted in 8 limbs (18%) and false negative results in 3 limbs (7%). Despite its being simple, rapid and noninvasive, its clinical usefulness is doubtful when performed according to the original method.

Thyroid Screening for Early Discharged Infants

PEDIATRICS ◽  
1996 ◽  
Vol 98 (1) ◽  
pp. 41-44
Author(s):  
Judy G. Saslow ◽  
Ernest M. Post ◽  
Carol A. Southard
Keyword(s):  
New Jersey ◽  
Congenital Hypothyroidism ◽  
False Positive ◽  
False Negative ◽  
Negative Results ◽  
Thyroid Screening ◽  
False Negative Results ◽  
Positive Results

Objective. As neonatal discharge before 24 hours of life becomes commonplace, the rejection of congenital hypothyroidism (CH) screening specimens obtained too early has created the need for numerous additional tests. We sought to determine whether the specimens obtained before 24 hours could be used safely. Methods. During a 31-day period we measured thyrotropin in all thyroid-screening specimens that had been obtained before 24 hours. We also examined the early specimens from every infant diagnosed in New Jersey with CH during 1993 or 1994. Results. Among the 663 specimens, those obtained at or before 12 hours and those from infants with birth weights less than 2500 g had too many low thyroxine results to be useful. Among the 515 specimens obtained at more than 12 to 24 hours from newborns weighing 2500 g or more, 37 (7%) had low thyroxine levels and 12 (2.3%) had thyrotropin levels of 20 µIU/mL (mU/L) or higher. Four hundred seventy-one of the 515 infants had subsequent specimens obtained at more than 24 hours, and none of the results were abnormal. There was no child weighing more than or equal to 2500 g who was diagnosed with CH in 1993 and 1994 whose specimen obtained at 24 hours or less was normal. Conclusions. Accepting specimens obtained at more than 12 to 24 hours from infants weighing 2500 g or more would have resulted in more than the usual number of false-positive results but no false-negative results. This would have decreased the requests for additional specimens by more than 90%.

scholarly journals Clinical Performance of SARS-CoV-2 Molecular Tests

2020 ◽  
Vol 58 (8) ◽  
Author(s):  
Daniel A. Green ◽  
Jason Zucker ◽  
Lars F. Westblade ◽  
Susan Whittier ◽  
Hanna Rennert ◽  
...  
Keyword(s):  
Clinical Performance ◽  
Severe Disease ◽  
False Negative ◽  
Patient Specific ◽  
Molecular Testing ◽  
Repeat Testing ◽  
Initial Testing ◽  
Molecular Assays ◽  
Negative Results ◽  
Positive Results

ABSTRACT Molecular testing for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the gold standard for diagnosis of coronavirus disease 2019 (COVID-19), but the clinical performance of these tests is still poorly understood, particularly with regard to disease course, patient-specific factors, and viral shedding. From 10 March to 1 May 2020, NewYork-Presbyterian laboratories performed 27,377 SARS-CoV-2 molecular assays from 22,338 patients. Repeat testing was performed for 3,432 patients, of which 2,413 had initial negative and 802 had initial positive results. Repeat-tested patients were more likely to have severe disease and low viral loads. The negative predictive value of the first-day result among repeat-tested patients was 81.3% The clinical sensitivity of SARS-CoV-2 molecular assays was estimated between 58% and 96%, depending on the unknown number of false-negative results in single-tested patients. Conversion to negative was unlikely to occur before 15 to 20 days after initial testing or 20 to 30 days after the onset of symptoms, with 50% conversion occurring at 28 days after initial testing. Conversion from first-day negative to positive results increased linearly with each day of testing, reaching 25% probability in 20 days. Sixty patients fluctuated between positive and negative results over several weeks, suggesting that caution is needed when single-test results are acted upon. In summary, our study provides estimates of the clinical performance of SARS-CoV-2 molecular assays and suggests time frames for appropriate repeat testing, namely, 15 to 20 days after a positive test and the same day or next 2 days after a negative test for patients with high suspicion for COVID-19.

scholarly journals Identification of etiological agents of selected bacterial and viral infections based on serological tests

2018 ◽  
Vol 72 ◽  
pp. 1162-1178
Author(s):  
Aleksandra Lewandowicz-Uszyńska ◽  
Piotr Naporowski ◽  
Gerard Pasternak ◽  
Danuta Witkowska
Keyword(s):  
False Positive ◽  
Cellular Response ◽  
Bacterial Infections ◽  
Viral Infections ◽  
False Negative ◽  
Main Role ◽  
Serological Tests ◽  
Negative Results ◽  
False Negative Results ◽  
Positive Results

The human immune system’s response to infection is closely related with the type of pathogen. First, a rapid, metabolically inexpensive and non-specific innate immunity is induced, then a specific acquired immunity is activated. In bacterial infections caused by intracellular pathogens, the main role is played by cellular response. In infections caused by bacterial extracellular pathogens, a crucial role is played by antibodies. The clinical symptoms of bacterial and viral infections very often are similar, which is why diagnosing them based only on medical history and physical examination is insufficient. To identify the etiological factors of infections differentiating media, biochemical tests, molecular methods and serological tests are used. The detection of microorganisms or their genetic material can be performed within a short time after the occurrence of an infection. The detection of antibodies is possible only in the appropriate time called the serological window. In a serological diagnostic of infections there are problems with an appropriate interpretation of obtained results. Cross-reactivity can give false positive results for the diagnosis of Chlamydophila pneumonia infection. The problem with the detection of Borrelia burgdorferi infection can be caused by a simultaneous coinfection with different spirochetes, syphilis, mononucleosis or HIV. In serological diagnostics of bacterial infections, the administration of antibiotics to patients before taking serum samples can be responsible for false negative results. Another reason for such results can be a weak humoral response in infected patients. In viral infections, false positive results can be caused by a coinfection of different viruses, especially from the same family or by bacterial or protozoal coinfections or by autoimmune diseases. False-negative results in viral infections often are caused by the early phase of an infection. To properly recognize an etiological factor of infection it is necessary to use an appropriate method, precision of test and collect samples at the appropriate time.

scholarly journals Suction sampling as a significant source of error in molecular analysis of predator diets

2011 ◽  
Vol 102 (3) ◽  
pp. 261-266 ◽  
Author(s):  
R.A. King ◽  
J.S. Davey ◽  
J.R. Bell ◽  
D.S. Read ◽  
D.A. Bohan ◽  
...  
Keyword(s):  
Molecular Analysis ◽  
False Positive ◽  
False Negative ◽  
Gut Contents ◽  
Predator Prey ◽  
Negative Results ◽  
False Negative Results ◽  
Sampling Protocols ◽  
Contradictory Evidence ◽  
Positive Results

AbstractThe molecular detection of predation is a fast growing field, allowing highly specific and sensitive detection of prey DNA within the gut contents or faeces of a predator. Like all molecular methods, this technique is prone to potential sources of error that can result in both false positive and false negative results. Here, we test the hypothesis that the use of suction samplers to collect predators from the field for later molecular analysis of predation will lead to high numbers of false positive results. We show that, contrary to previous published work, the use of suction samplers resulted in previously starved predators testing positive for aphid and collembolan DNA, either as a results of ectopic contamination or active predation in the collecting cup/bag. The contradictory evidence for false positive results, across different sampling protocols, sampling devices and different predator-prey systems, highlights the need for experimentation prior to mass field collections of predators to find techniques that minimise the risk of false positives.

The spot test is not a reliable screening procedure for mucopolysaccharidoses

1991 ◽  
Vol 37 (4) ◽  
pp. 572-575 ◽  
Author(s):  
J G N de Jong ◽  
J J F Hasselman ◽  
A A J van Landeghem ◽  
H L Vader ◽  
R A Wevers
Keyword(s):  
False Positive ◽  
False Negative ◽  
Spot Test ◽  
Urine Samples ◽  
Screening Procedure ◽  
Negative Results ◽  
False Negative Results ◽  
Spot Tests ◽  
Metabolic Screening ◽  
Positive Results

Abstract To check the reliability of the Ames MPS paper spot test, which is based on the Azure A dye, we sent a series of urine samples to three laboratories where the spot test is part of the metabolic screening for mucopolysaccharidoses. In these laboratories false-negative results ranged between 19% and 35% and false-positive results ranged between 12% and 29% of all samples submitted. In contrast, the quantitative dimethylmethylene blue test (Clin Chem 1989;35:1472-7) detected an increased glycosaminoglycan content in all urine samples from mucopolysaccharidosis patients and gave no false-positive results. In the latter procedure, glycosaminoglycan content is expressed per millimole of creatinine, and age-dependent reference values are used. We conclude that the Ames spot test and other spot tests are unreliable as a screening procedure for mucopolysaccharidoses and should not be used to screen for these diseases.

Cord Plasma α-Fetoprotein Values and Neonatal Jaundice

PEDIATRICS ◽  
1984 ◽  
Vol 74 (6) ◽  
pp. 1065-1068 ◽  
Author(s):  
K. L. Tan ◽  
A. Loganath ◽  
A. C. Roy ◽  
H. H. Goh ◽  
S. M. Karim ◽  
...  
Keyword(s):  
High Risk ◽  
False Positive ◽  
Neonatal Jaundice ◽  
False Negative ◽  
Negative Results ◽  
Cord Plasma ◽  
False Negative Results ◽  
The Mean ◽  
Glucose 6 Phosphate Dehydrogenase ◽  
Positive Results

Umbilical cord plasma α-fetoprotein (AFP) values were determined in 127 infants with hyperbilirubinemia (56 glucose-6-phosphate dehydrogenase (G-6-PD) deficient and 71 G-6-PD normal) and 136 control subjects (73 G-6-PD deficient and 63 G-6-PD normal). The mean α-fetoprotein value of 173 ± 35.2 (SD) mg/L for the group of infants with hyperbilirubinemia was significantly greater than that (122 ± 21.7 mg/L) for the control infants (P < .001). G-6-PD status and sex did not significantly affect the α-fetoprotein values. Using an α-fetoprotein level of 130 mg/L as a "cut-off" value, the incidence of false-positive results was 25.5% and the incidence of false-negative results was 11.8%. This test can be used as a screening procedure to detect infants at high risk for hyperbilirubinemia.

scholarly journals Simplified chromatographic separation of immunoglobulin M from G and its application to toxoplasma indirect immunofluorescence

1979 ◽  
Vol 9 (2) ◽  
pp. 170-174
Author(s):  
N Pyndiah ◽  
U Krech ◽  
P Price ◽  
J Wilhelm
Keyword(s):  
False Positive ◽  
False Negative ◽  
Gel Filtration ◽  
Immunoglobulin M ◽  
Antibody Technique ◽  
Negative Results ◽  
False Negative Results ◽  
A Prospective Study ◽  
Indirect Immunofluorescent ◽  
Positive Results

The indirect immunofluorescent (IIF) antibody technique for the detection of Toxoplasma gondii immunoglobulin M (IgM) often gives false negative results, probably due to the competition between IgG and IgM. We therefore adapted a gel filtration procedure for the separation of IgG and IgM to a routine diagnostic test capable handling at least 10 sera per day and requiring only 50 microliters of serum. The results from 108 sera having positive complement fixation titers for Toxoplasma showed that 17 were IgM positive when the whole serum was tested by IIF compared with 55 positive when the IgM fraction was used. Sera with antideoxyribonucleic acid titers do not give false positive results after fractionation, and the removal of IgG eliminates false positive results due to rheumatoid factor. A prospective study showed that Toxoplasma IgM may persist up to 9 months.

scholarly journals Evaluation of a rapid dipstick test, Malar-CheckTM, for the diagnosis of Plasmodium falciparum malaria in Brazil

2002 ◽  
Vol 44 (5) ◽  
pp. 293-296 ◽  
Author(s):  
Priscilla Elisangela AVILA ◽  
Karin KIRCHGATTER ◽  
Karen Cristina S. BRUNIALTI ◽  
Alessandra M. OLIVEIRA ◽  
Rinaldo F. SICILIANO ◽  
...  
Keyword(s):  
Plasmodium Falciparum ◽  
False Positive ◽  
False Negative ◽  
Plasmodium Falciparum Malaria ◽  
Dipstick Test ◽  
True Negative ◽  
Disease Evolution ◽  
Negative Results ◽  
False Positive Test ◽  
Positive Results

The present study was carried out to evaluate the Malar-CheckTM Pf test, an immunochromatographic assay that detects Plasmodium falciparum Histidine Rich Protein II, does not require equipment, and is easy and rapid to perform. In dilution assays performed to test sensitivity against known parasite density, Malar-CheckTMwere compared with thick blood smear (TBS), the gold standard for diagnosis. Palo Alto isolate or P. falciparum blood from patients with different parasitemias was used. The average cut-off points for each technique in three independent experiments were 12 and 71 parasites/mm³ (TBS and Malar-CheckTM, respectively). In the field assays, samples were collected from patients with fever who visited endemic regions. Compared to TBS, Malar-CheckTMyielded true-positive results in 38 patients, false-positive results in 3, true-negative results in 23, and false-negative result in 1. Malar-CheckTMperformed with samples from falciparum-infected patients after treatment showed persistence of antigen up to 30 days. Malar-CheckTM should aid the diagnosis of P. falciparum in remote areas and improve routine diagnosis even when microscopy is available. Previous P. falciparum infection, which can determine a false-positive test in cured individuals, should be considered. The prompt results obtained with the Malar-CheckTM for early diagnosis could avoid disease evolution to severe cases.

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