Incidence Of False-positive Tests Research Articles

Facile synthesis of 14 C-nitrofurazone from 14 C-urea.

The veterinary drug nitrofurazone (5-nitro-2-furaldehyde semicarbazone) exhibits excellent antimicrobial properties but its application in food-producing animals is prohibited. The illegal use of nitrofurazone is regularly monitored by food regulatory agencies. Currently, semicarbazide (SEM) is used as a marker of nitrofurazone exposure. However, the use of SEM as a marker of nitrofurazone is under scrutiny after evidence of a high incidence of false positive tests. To overcome the current dilemma, it is necessary to identify a nitrofurazone-specific marker analyte which requires conducting nitrofurazone metabolism studies in food-producing animals. The use of carbon-14 labeled nitrofurazone would facilitate metabolism studies and structural elucidation of nitrofurazone metabolites of possible utility as a marker compound. In the present work, a synthetic method is described to procure radiolabeled nitrofurazone that incorporates 14 C- carbon at the semicarbazide moiety. The method incorporates 14 C-carbon via employing readily available and more economically affordable [14 C]-urea compared with [14 C]-semicarbazide. To the best of our knowledge, there is no report on the synthesis of 5-nitro-2-furaldehyde [14 C]-semicarbazone from 14 C-urea. The developed method involves monoamination of [14 C]-urea followed by a condensation reaction with 5-nitro-2-furaldehyde to produce 5-nitro-2-furaldehyde [14 C]-semicarbazone in 85% yield with greater than 98% radiochemical purity.

The Performance of the Approved Screening Device, the Alcotest® 7410 GLC in the Field: Low Incidence of False Positive Results in the Identification of Drinking Drivers

ABSTRACTA retrospective field study was conducted of 811 drinking drivers in the city of Toronto between January 1st 1998 and December 31st 1999 who had a breath alcohol concentration (BrAC) >0.099 g/210 L as determined by the Alcotest® 7410 GLC, the approved screening device (ASD). To determine the false positive rate of the ASD, its results were compared to the BrACs subsequently determined by the Intoxilyzer® 5000C, the evidential approved instrument. The BrACs determined by the Intoxilyzer® 5000C ranged between 0.000 and 0.310 g/210 L (mean 0.134 g/210 L). Seventeen drivers (2.1%) had a BrAC < 0.08 g/210 L and 117 drivers (14.4%) had a BrAC< 0.100 g/210 L at the time of the Intoxilyzer® 5000C test. When the BrACs are corrected for the time delay (0.1 to 2.6 hours) between the ASD and Intoxilyzer® 5000C tests, only two drivers (0.2%) had an estimated BrAC < 0.080 g/210 L and twelve drivers (1.5%) had a BrAC < 0.100 g/210 L. Thus, the Alcotest® 7410 GLC operated under field conditions has a low incidence of false positive tests.

Influences of perinatal factors on cord blood thyroid-stimulating hormone level.

Cord blood thyroid-stimulating hormone level is affected by various perinatal factors. The aim of this study is to investigate the relative impact of these factors on the cord blood thyroid-stimulating hormone results in singleton pregnancies. The study group consisted of 20,086 consecutive singleton deliveries over a 3 year period. The effect of mode of delivery, infant sex, gestation at birth, birth weight, and duration of labor on the incidence of false elevation of cord blood thyroid-stimulating hormone was assessed by univariate analysis and logistic regression. There was an independent positive association between false elevation of cord blood thyroid-stimulating hormone (> or =15.0 mIU/L) and birth weight (p=0.005), male infant sex (p<0.001), and instrumental delivery (p<0.001). Both elective and emergency cesarean section were negatively associated with elevated cord thyroid-stimulating hormone level (p<0.001). When the cutoff level was raised to 40.0 mIU/L, none of the variables examined were significant. The incidence of false positive tests (> or =15.0 mIU/L) was higher in neonates born by cesarean section for failed instrumental delivery and fetal distress than for failure to progress of labor (34.7% vs 4.5% vs 1.3% respectively, p<0.001). While the incidence of false positive screening was significantly affected by various perinatal factors when the thyroid-stimulating hormone cutoff level is low, it was unaffected at a high cutoff level. The present study also provides further evidence that cord blood thyroid-stimulating hormone level reflects fetal response to perinatal stress events.

Optimal late potential criteria for reducing false positive signal-averaged electrocardiograms

The purposes of this study were to determine for signal-averaged electrocardiograms in normal subjects: (1) the incidence of false positives for various filter frequencies and late potential criteria and (2) reproducibility over time. In 46 normal volunteers, the QRS vector magnitude was bidirectionally high-pass filtered at 25, 40, and 100 Hz. As high-pass filter frequency increased, QRS duration decreased from 98 ± 9 to 92 ± 9 msec ( p < 0.0001), terminal QRS root mean square voltage decreased from 60 ± 41 to 14 ± 9 μV ( p < 0.0001), and terminal QRS low amplitude signal duration increased from 27 ± 7 to 41 ± 14 msec ( p < 0.0001). For individual parameters, the incidence of false positive tests ranged from 2% to 41%, whereas there were no false positive tests for the combination of abnormal QRS duration plus either root mean square voltage or low amplitude signal duration. Measurements were repeated after 6.4 ± 0.3 months in 26 subjects and were highly reproducible at all filter settings. The potentially high incidence of false positive tests with some criteria has important implications for the use of signal-averaged electrocardiography as a screening test in patient populations with various arrhythmia risks.

Correlation of Nonspecific Immune Monitoring with Rejection or Impaired Function of Renal Allografts

Two nonspecific immunological assays were combined with radionuclide scanning to monitor 113 patients thrice weekly following allotransplantation. The nonspecific immune assays included measurement of the percentage of active T rosette-forming cells (% A-T RFCs) and spontaneous blastogenesis (SB). An increase in SB and decrease in % A-T RFCs (greater than 1 sd of normal controls) constituted an immune event. The immune parameters were correlated with thrice weekly radionuclide studies which were computer analyzed for glomerular and tubular function. Alteration of the immunological and radionuclide parameters significantly correlated (P less than 0.001) with 90 rejection episodes displayed by 72 nonantithymocyte globulin (ATG)-treated renal allograft recipients during the first 30 postoperative days. In the absence of clinically defined rejection, changes in immune parameters correlated with (1) decline of radionuclide parameters and (2) alterations in weight, temperature, creatinine clearance, and serum creatinine, suggesting subclinical events. As a result of the effects of ATG on lymphocytes, a similar comparison could not be made for 41 other patients treated with this immunosuppressive drug. The incidence of false positive tests was 12.7%. Thus, the combination of two nonspecific immune parameters, % A-T RFCs and SB, with computerized analysis of radionuclide scans may afford a reliable index to diagnose early rejection or impaired function of renal allografts.

Correlation of nonspecific immune monitoring with rejection or impaired function of renal allografts.

Two nonspecific immunological assays were combined with radionuclide scanning to monitor 113 patients thrice weekly following allotransplantation. The nonspecific immune assays included measurement of the percentage of active T rosette-forming cells (% A-T RFCs) and spontaneous blastogenesis (SB). An increase in SB and decrease in % A-T RFCs (greater than 1 sd of normal controls) constituted an immune event. The immune parameters were correlated with thrice weekly radionuclide studies which were computer analyzed for glomerular and tubular function. Alteration of the immunological and radionuclide parameters significantly correlated (P less than 0.001) with 90 rejection episodes displayed by 72 nonantithymocyte globulin (ATG)-treated renal allograft recipients during the first 30 postoperative days. In the absence of clinically defined rejection, changes in immune parameters correlated with (1) decline of radionuclide parameters and (2) alterations in weight, temperature, creatinine clearance, and serum creatinine, suggesting subclinical events. As a result of the effects of ATG on lymphocytes, a similar comparison could not be made for 41 other patients treated with this immunosuppressive drug. The incidence of false positive tests was 12.7%. Thus, the combination of two nonspecific immune parameters, % A-T RFCs and SB, with computerized analysis of radionuclide scans may afford a reliable index to diagnose early rejection or impaired function of renal allografts.