High Incidence of Significant Urinary Ascorbic Acid Concentrations in a West Coast Population—Implications for Routine Urinalysis

1992 ◽  
Vol 38 (3) ◽  
pp. 426-431 ◽  
Author(s):  
M L Brigden ◽  
D Edgell ◽  
M McPherson ◽  
A Leadbeater ◽  
G Hoag
Keyword(s):  
Ascorbic Acid ◽  
Vitamin C ◽  
False Negative ◽  
High Rate ◽  
High Power Field ◽  
Glucose Testing ◽  
Negative Results ◽  
False Negative Results ◽  
High Incidence ◽  
The Mean

Abstract Examination of 4379 routine urinalysis specimens with dipsticks sensitive to ascorbic acid showed that 22.8% were positive specimens. The mean urinary vitamin C concentration in this population was 2120 mumol/L. There was a high rate of false-negative dipstick results for hemoglobin in patients with vitamin C in the urine. The highest false-negative rates were observed in urine samples containing less than 50 erythrocytes per high-power field. In further experiments when volunteers consumed supplemental oral USP vitamin C at doses of 100, 250, 500, and 1000 mg or vitamin C-containing fruit juices, even the lowest doses of oral vitamin C or juice resulted in sufficient urinary vitamin C to produce false-negative dipstick results in hemoglobin and glucose testing. To prevent potentially dangerous false-negative results, screening urinalysis protocols relying only on dipstick testing should include a check for urinary vitamin C or use a dipstick that is not subject to vitamin C interference.

False-negative results for urinary phenothiazines and imipramine in Forrest's qualitative assays.

1980 ◽  
Vol 26 (2) ◽  
pp. 345-347 ◽  
Author(s):  
G P James ◽  
M H DJang ◽  
H H Hamilton
Keyword(s):  
Ascorbic Acid ◽  
Ion Exchange ◽  
Exchange Resin ◽  
Anion Exchange Resin ◽  
False Negative ◽  
Ion Exchange Chromatography ◽  
Exchange Chromatography ◽  
Negative Results ◽  
False Negative Results

Abstract When a series of patients' urine samples supplemented in vitro with chlorpromazine or imipramine was assayed with the Forrest qualitative assays, we observed an occasional false-negative result, which we found was attributable to interference by ascorbic acid. It interferes with the reagent, not with the analytes, in both assays. We easily eliminated this interference with the phenothiazine test by using an anion-exchange resin. Eliminating the interference with the assay for imipramine, however, is more difficult; false-negative results can be obtained even after ion-exchange chromatography if the imipramine concentration is less than 50 mg/L.

scholarly journals Trueness evaluation and verification of inter-assay agreement of serum folate measuring systems

2020 ◽  
Vol 58 (10) ◽  
pp. 1697-1705
Author(s):  
Federica Braga ◽  
Erika Frusciante ◽  
Simona Ferraro ◽  
Mauro Panteghini
Keyword(s):  
False Negative ◽  
Serum Folate ◽  
Clinical Samples ◽  
Measuring Systems ◽  
Negative Results ◽  
False Negative Results ◽  
Performance Specifications ◽  
The Mean ◽  
Intercomparison Study ◽  
Is Value

AbstractBackgroundDefinitive data to establish if the use of the WHO International Standard (IS) 03/178 as a common calibrator of commercial measuring systems (MSs) has improved the harmonization of serum total folate (tFOL) measurements to a clinically suitable level are lacking. Here, we report the results of an intercomparison study aimed to verify if the current inter-assay variability is acceptable for clinical application of tFOL testing.MethodsAfter confirming their commutability, the IS 03/178 and National Institute for Standards and Technology SRM 3949 L1 were used for evaluating the correctness of traceability implementation by manufacturers and the MSs trueness, respectively. The inter-assay agreement was verified using 20 patient pools. The measurement uncertainty (U) of tFOL measurements on clinical samples was also estimated. An outcome-based model for defining desirable performance specifications for bias and imprecision for serum tFOL measurements was applied.ResultsThe majority of evaluated MSs overestimated the WHO IS value of +5% or more with the risk to produce an unacceptably high number of false-negative results in clinical practice. The mean inter-assay CV on all pools and on those with tFOL values >3.0 μg/L (n = 15) was 12.5% and 7.1%, respectively. In neither case the goal of 3.0% was fulfilled. The residual bias resulted in an excessive U of tFOL measurement on clinical samples.ConclusionsThe implementation of traceability of tFOL MSs to the WHO IS 03/178 is currently inadequate, resulting in an inter-assay variability that does not permit the use of a common threshold for detecting folate deficiency.

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.

False-negative results for urinary phenothiazines and imipramine in Forrest's qualitative assays.

1980 ◽  
Vol 26 (2) ◽  
pp. 345-347
Author(s):  
G P James ◽  
M H DJang ◽  
H H Hamilton
Keyword(s):  
Ascorbic Acid ◽  
Ion Exchange ◽  
Exchange Resin ◽  
Anion Exchange Resin ◽  
False Negative ◽  
Ion Exchange Chromatography ◽  
Exchange Chromatography ◽  
Negative Results ◽  
False Negative Results

Abstract When a series of patients' urine samples supplemented in vitro with chlorpromazine or imipramine was assayed with the Forrest qualitative assays, we observed an occasional false-negative result, which we found was attributable to interference by ascorbic acid. It interferes with the reagent, not with the analytes, in both assays. We easily eliminated this interference with the phenothiazine test by using an anion-exchange resin. Eliminating the interference with the assay for imipramine, however, is more difficult; false-negative results can be obtained even after ion-exchange chromatography if the imipramine concentration is less than 50 mg/L.

scholarly journals A 10-Year Retrospective Comparison of Two Target Sequences, REP-529 and B1, for Toxoplasma gondii Detection by Quantitative PCR

2015 ◽  
Vol 53 (4) ◽  
pp. 1294-1300 ◽  
Author(s):  
Sorya Belaz ◽  
Jean-Pierre Gangneux ◽  
Peggy Dupretz ◽  
Claude Guiguen ◽  
Florence Robert-Gangneux
Keyword(s):  
Quantitative Pcr ◽  
False Negative ◽  
Congenital Toxoplasmosis ◽  
Poor Performance ◽  
Relative Sensitivity ◽  
Repeated Sequence ◽  
Content Type ◽  
Negative Results ◽  
False Negative Results ◽  
The Mean

This study aimed to evaluate the repeated sequence REP-529 compared to that of the B1 gene in the molecular diagnosis of toxoplasmosis by quantitative PCR (qPCR) in routine diagnosis. Over a 10-year period (2003 to 2013), all patients prospectively diagnosed with a positive REP-529 qPCR result for toxoplasmosis were included. All DNA samples (76 samples from 56 patients) were simultaneously tested using the two qPCR methods (REP-529 and B1). The mean cycle threshold (CT) obtained with the B1 qPCR was significantly higher (+4.71 cycles) than that obtained with REP-529 qPCR (P< 0.0001). Thirty-one out of 69 extracts (45.6%) positive with REP-529 qPCR were not amplified with the B1 qPCR (relative sensitivity of 54.4% compared to that with REP-529), yielding false-negative results with 15/28 placenta, 5 cord blood, 2 amniotic fluid, 4 cerebrospinal fluid, 1 aqueous humor, 2 lymph node puncture, and 1 abortion product sample. This defect in sensitivity would have left 20/56 patients undiagnosed, distributed as follows: 12/40 congenital toxoplasmosis, 4/5 cerebral toxoplasmosis, 2/8 patients with retinochoroiditis, and 2 patients with chronic lymphadenopathy. This poor performance of B1 qPCR might be related to low parasite loads, since the meanToxoplasmaquantification in extracts with B1 false-negative results was 0.4 parasite/reaction. These results clearly show the superiority of the REP-529 sequence in the diagnosis of toxoplasmosis by PCR and suggest that this target should be adopted as part of the standardization of the PCR assay.

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