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PubMed2000

Assessing mammographers' accuracy. A comparison of clinical and test performance.

Direct estimation of mammographers' clinical accuracy requires the ability to capture screening assessments and correctly identify which screened women have breast cancer. This clinical information is often unavailable and when it is available its observational nature can cause analytic problems. Problems with clinical data have led some researchers to evaluate mammographers using a single set of films. Research based on these test film sets implicitly assumes a correspondence between mammographers' accuracy in the test setting and their accuracy in a clinical setting. However, there is no evidence supporting this basic assumption. In this article we use hierarchical models and data from 27 mammographers to directly compare accuracy estimated from clinical practice data to accuracy estimated from a test film set. We found moderate positive correlation [ rho; = 0.206 with 95% credible interval (-0.142-0. 488)] between mammographers' overall preponderance to call a mammogram positive. However, we found no evidence of correlation between clinical and test accuracy [ rho; = -0.025 with 95% credible interval (-0.484-0.447)]. This study is limited by the relatively small number of mammographers evaluated, by the somewhat restricted range of observed sensitivities and specificities, and by differences in the types of films evaluated in test and clinical datasets. Nonetheless, these findings raise important questions about how mammographer accuracy should be measured.

Adult↗

PubMed1994

An index for diagnostic accuracy in the multiple disease setting.

RATIONALE AND OBJECTIVES: Evaluation of diagnostic accuracy in the clinical environment should entail some assessment of performance in patients with multiple abnormalities. Although receiver operating characteristic (ROC) curves often are used to assess the diagnostic accuracy of imaging systems, the concept is not easily generalizable to patients with multiple abnormalities. I propose a measure of diagnostic accuracy that is a generalization of the area under the ROC curve for a single disease. METHODS: The proposed measure of diagnostic accuracy is a weighted average of the area under individual ROC curves for the single disease setting and of components representing areas under ROC curves constructed for patients with multiple diseases. Several options are discussed for scoring the presence of abnormality for patients who have two or more abnormalities. RESULTS: Methods of estimating diagnostic accuracy are demonstrated on a set of data in which more than one third of the abnormal cases included multiple abnormalities of chest disease. CONCLUSION: An easy-to-use method is given to estimate diagnostic accuracy in the multiple abnormality setting. This should make it easier to incorporate cases with multiple abnormalities when assessing the diagnostic accuracy of imaging systems.

Diagnosis, Differential↗

PubMed2002

Diagnostic accuracy of dermoscopy.

The accuracy of the dinical diagnosis of cutaneous melanoma with the unaided eye is only about 60%. Dermoscopy, a non-invasive, in vivo technique for the microscopic examination of pigmented skin lesions, has the potential to improve the diagnostic accuracy. Our objectives were to review previous publications, to compare the accuracy of melanoma diagnosis with and without dermoscopy, and to assess the influence of study characteristics on the diagnostic accuracy. We searched for publications between 1987 and 2000 and identified 27 studies eligible for meta-analysis. The diagnostic accuracy for melanoma was significantly higher with dermoscopy than without this technique (log odds ratio 4.0 [95% CI 3.0 to 5.1] versus 2.7 [1.9 to 3.4]; an improvement of 49%, p = 0.001). The diagnostic accuracy of dermoscopy significantly depended on the degree of experience of the examiners. Dermoscopy by untrained or less experienced examiners was no better than clinical inspection without dermoscopy. The diagnostic performance of dermoscopy improved when the diagnosis was made by a group of examiners in consensus and diminished as the prevalence of melanoma increased. A comparison of various diagnostic algorithms for dermoscopy showed no significant differences in their diagnostic performance. A thorough appraisal of the study characteristics showed that most of the studies were potentially influenced by verification bias. In conclusion, dermoscopy improves the diagnostic accuracy for melanoma in comparison with inspection by the unaided eye, but only for experienced examiners.

Dermatology↗

PubMed2004

Lessons in molecular recognition: the effects of ligand and protein flexibility on molecular docking accuracy.

The key to success for computational tools used in structure-based drug design is the ability to accurately place or "dock" a ligand in the binding pocket of the target of interest. In this report we examine the effect of several factors on docking accuracy, including ligand and protein flexibility. To examine ligand flexibility in an unbiased fashion, a test set of 41 ligand-protein cocomplex X-ray structures were assembled that represent a diversity of size, flexibility, and polarity with respect to the ligands. Four docking algorithms, DOCK, FlexX, GOLD, and CDOCKER, were applied to the test set, and the results were examined in terms of the ability to reproduce X-ray ligand positions within 2.0A heavy atom root-mean-square deviation. Overall, each method performed well (>50% accuracy) but for all methods it was found that docking accuracy decreased substantially for ligands with eight or more rotatable bonds. Only CDOCKER was able to accurately dock most of those ligands with eight or more rotatable bonds (71% accuracy rate). A second test set of structures was gathered to examine how protein flexibility influences docking accuracy. CDOCKER was applied to X-ray structures of trypsin, thrombin, and HIV-1-protease, using protein structures bound to several ligands and also the unbound (apo) form. Docking experiments of each ligand to one "average" structure and to the apo form were carried out, and the results were compared to docking each ligand back to its originating structure. The results show that docking accuracy falls off dramatically if one uses an average or apo structure. In fact, it is shown that the drop in docking accuracy mirrors the degree to which the protein moves upon ligand binding.

Algorithms↗

PubMed1997

Factors influencing the diagnostic accuracy of dobutamine stress echocardiography.

BACKGROUND: While Dobutamine stress echocardiography is a well established tool, the range of the diagnostic accuracy found in the literature is rather large. The main reason for this is the fact, that different test protocols were used. Aim of this study was to assess the effects of both addition of atropine as well as consideration of a hyperdynamic response while interpreting the stress echocardiogram on the diagnostic accuracy. METHODS AND RESULTS: 120 consecutive patients were examined and divided into the following groups: A) achieving their age predicted heart rate with dobutamine, B) termination of the test due to ischemia, C1) negative test without reaching the predicted heart rate, and C2) C1 following addition of atropine. All of the echocardiograms were analyzed twice: 1) regarding the lack of a hyperdynamic response to dobutamine as ischemia (Hyper analysis), and 2) ignoring the hypercontractility (Conventional analysis). The accuracy of A and B were 88% and 90% resp. Group C1 had a very poor accuracy of 60%. This rose significantly (p < 0.01) after atropine (C2 = 84%), without leading to an increase of adverse effects. Conventional wallmotion analysis lead to an overall accuracy of 87% (groups A, B, and C2), while Hyper analysis showed an accuracy of 90% (p < 0.01). CONCLUSIONS: To achieve a high accuracy Dobutamine stress echocardiography should always be combined with atropine to reach a target heart rate. The wallmotion analysis should be based on the assumption that a hyperdynamic response to dobutamine is normal, while its lack is indicative of ischemia.

Adult↗

PubMed1997

Bench test assessment of dosage accuracy and measurement inaccuracy in nitric oxide inhalational therapy during high frequency oscillatory ventilation.

OBJECTIVE: The objective of this study is to determine the accuracy and precision of chemiluminescence and electrochemical nitric oxide (NO) measurements and accuracy of NO dosage with electronic mass flow controllers (MFC) versus rotameters during NO inhalational therapy. METHODS: NO flow was delivered to a high frequency oscillator and mixed with ventilator flow. NO and NO2 concentrations were measured simultaneously with a standard chemiluminescence analyzer and a modified electrochemical analyzer. Dosage accuracy was assessed with gas flows adjusted with either MFC's or rotameters. Accuracy of both analyzers was validated with both NO and ventilator flow regulated with a MFC. RESULTS: In dry air, without pulsatile pressure, MFC controlled NO and ventilator flow resulted in an accuracy expressed as the ratio of calculated concentration to measured concentration (RCM) of 0.995 (CI: 0.983-0.988) when measured with chemiluminescence. When the ventilator rotameter was used instead of a MFC, RCM was 0.856 (CI: 0.835-0.877). With a rotameter for both NO and ventilator flow, RCM increased to 1.175 (CI: 0.793-1.740) with an increase of confidence interval limits. Chemiluminescence was sensitive to humidification of the ventilatory gases (p < 0.05), slightly sensitive to the addition of oxygen and to pulsatile pressure (not significant). RCM obtained with the modified electrochemical analyzer was in close agreement with chemiluminescence RCM, although 95% CI were wider with electrochemical analysis. CONCLUSIONS: During high frequency oscillatory ventilation (HFOV), standard rotameter flow control of both NO and ventilator flow results in unpredictable NO concentrations that would be clinically unacceptable. When one MFC was used for NO flow control, with ventilator flow controlled with a rotameter, this resulted in moderate dosage accuracy. To achieve a still higher accuracy, MFC flow control for both NO and ventilator flow is indicated. During HFOV, standard chemiluminescence analyzers cannot be considered to be the gold standard for determination of the NO concentration delivered. Measurement of NO concentration may not be mandatory for determination of inhaled NO dose during HFOV, but may be used to monitor for unsafe or unwanted events.

Administration, Inhalation↗

PubMed2003

A longitudinal study of self-assessment accuracy.

AIM: Although studies have examined medical students' ability to self-assess their performance, there are few longitudinal studies that document the stability of self-assessment accuracy over time. This study compares actual and estimated examination performance for three classes during their first 3 years of medical school. METHODS: Students assessed their performance on classroom examinations and objective structured clinical examination (OSCE) stations. Each self-assessment was then contrasted with their actual performance using idiographic (within-subject) methods to define three measures of self-assessment accuracy: bias (arithmetic differences of actual and estimated scores), deviation (absolute differences of actual and estimated scores), and covariation (correlation of actual and estimated scores). These measures were computed for four intervals over the course of 3 years. Multivariate analyses of variance and correlational analyses were used to evaluate the stability of these measures. RESULTS: Self-assessment accuracy measures were relatively stable over the first 2 years of medical school with a decease occurring in the third year. However, the correlational analyses indicated that the stability of self-assessment accuracy was comparable to the stability of actual performance over this same period. CONCLUSION: The apparent decline in accuracy in the third year may reflect the transition from familiar classroom-based examinations to the substantially different clinical examination tasks of the third year OSCE. However, the stability of self-assessment accuracy compares favorably with the stability of actual performance over this period. These results suggest that self-assessment accuracy is a relatively stable individual characteristic that may be influenced by task familiarity.

Chi-Square Distribution↗

PubMed2001

Training novice clinicians improves observation accuracy of the upper extremity after stroke.

OBJECTIVES: To determine whether training influenced the accuracy of observational kinematic assessment (OKA) of hemiplegic upper extremity impairment and to elucidate the contribution of knowledge of results to learning. DESIGN: Intervention study; before-after testing of OKA accuracy after training, using 2 trained groups (with knowledge of results, KR group; without, NKR group) and 1 control group with a 1-week retention test. SETTING: Tertiary teaching. PARTICIPANTS: Fifty-one first-year physical therapy student volunteers acted as observers. They were ranked on pretest accuracy and then randomized into groups. A consecutive sample of 11 stroke patients and 4 nondisabled subjects acted as performers. INTERVENTIONS: Performers were videotaped with 3 cameras and upper extremity kinematics derived using computer-assisted motion analysis. Training and test videotapes were generated. Training groups received video-based training of path indirectness accuracy on 4 occasions. The OKA accuracy of all observers' judgments of speed, jerkiness, and path indirectness were examined pretest and posttest. MAIN OUTCOME MEASURE: Accuracy reported as mean absolute error, which was calculated as difference between observers' judgments and criterion kinematic values. RESULTS: The KR and NKR groups showed reduction in mean absolute error after training of 34.8% and 6.2%, respectively. Improvements were retained after a 1-week no intervention period. Transfer to trained, but not untrained kinematic parameters occurred. The control group did not change. CONCLUSIONS: OKA accuracy is susceptible to training and knowledge of results aids learning. However, training is task specific.

Adult↗

PubMed2006

Optimization and use of peptide mass measurement accuracy in shotgun proteomics.

Mass spectrometers that provide high mass accuracy such as FT-ICR instruments are increasingly used in proteomic studies. Although the importance of accurately determined molecular masses for the identification of biomolecules is generally accepted, its role in the analysis of shotgun proteomic data has not been thoroughly studied. To gain insight into this role, we used a hybrid linear quadrupole ion trap/FT-ICR (LTQ FT) mass spectrometer for LC-MS/MS analysis of a highly complex peptide mixture derived from a fraction of the yeast proteome. We applied three data-dependent MS/MS acquisition methods. The FT-ICR part of the hybrid mass spectrometer was either not exploited, used only for survey MS scans, or also used for acquiring selected ion monitoring scans to optimize mass accuracy. MS/MS data were assigned with the SEQUEST algorithm, and peptide identifications were validated by estimating the number of incorrect assignments using the composite target/decoy database search strategy. We developed a simple mass calibration strategy exploiting polydimethylcyclosiloxane background ions as calibrant ions. This strategy allowed us to substantially improve mass accuracy without reducing the number of MS/MS spectra acquired in an LC-MS/MS run. The benefits of high mass accuracy were greatest for assigning MS/MS spectra with low signal-to-noise ratios and for assigning phosphopeptides. Confident peptide identification rates from these data sets could be doubled by the use of mass accuracy information. It was also shown that improving mass accuracy at a cost to the MS/MS acquisition rate substantially lowered the sensitivity of LC-MS/MS analyses. The use of FT-ICR selected ion monitoring scans to maximize mass accuracy reduced the number of protein identifications by 40%.

Calibration↗

PubMed1986

Absolute error revisited: an accuracy indicator in disguise.

When target accuracy is defined as the probability that an individual will respond to an accuracy task within a fixed distance around the target, then the composite error measures, E and AE, are shown to be fairly strong indicators of target accuracy in a relative sense. When AE and E are compared, AE is shown to be an even stronger accuracy indicator than E for most reasonable accuracy requirements. This, plus the fact that AE has certain desirable properties in ANOVA procedures, suggests that AE is a good, composite measure of target accuracy and should be analyzed first to determine if target accuracy differences exist. Subsequent analyses of bias and/or variability are then recommended.

Journal Article↗

PubMed2004

The accuracy of risk scores in predicting preterm birth--a systematic review.

This review aims to determine the accuracy with which published risk scores predict spontaneous preterm birth in pregnant women. Studies were identified without language restrictions through nine different databases (up to June 2002), and manual searching of bibliographies of known primary and review articles. Two reviewers selected studies independently and extracted data on their characteristics, quality and accuracy. Accuracy data were used to form 2 x 2 contingency tables of the results of risk scoring with spontaneous preterm birth as the reference standard. Heterogeneity was assessed and its reasons were explored. Summary estimates of accuracy were produced within clinically appropriate subgroups. There were 19 primary accuracy articles that met the selection criteria, including a total of 67390 women. There are 12 different risk-scoring systems, the one developed by Creasy being the most commonly evaluated. Quality features of an ideal study, such as blinding and consecutive enrolment, were frequently missing from the included studies, no study fulfilled all criteria for high quality study, and there was heterogeneity between their accuracy estimates. The reference standard most often used was birth before 37 weeks' gestation. The point estimates for the likelihood ratios (LRs) varied widely among the studies. LRs for an abnormal score (LR+) ranged from 1.0 (95% confidence interval (CI) 0.6-1.4) to 38.8 (95% CI 23.5-63.9) while that for a normal score (LR-) ranged from 0.1 (95% CI 0.02-0.6) to 1.2 (95% CI 0.9-1.6). In otherwise asymptomatic women, risk scoring in early pregnancy has a wide range of accuracy in predicting spontaneous preterm birth before 37 weeks' gestation. The evidence is of a relatively poor quality and lacks clinically important reference standards.

Female↗

PubMed2006

Multiple sequence alignment accuracy and phylogenetic inference.

Phylogenies are often thought to be more dependent upon the specifics of the sequence alignment rather than on the method of reconstruction. Simulation of sequences containing insertion and deletion events was performed in order to determine the role that alignment accuracy plays during phylogenetic inference. Data sets were simulated for pectinate, balanced, and random tree shapes under different conditions (ultrametric equal branch length, ultrametric random branch length, nonultrametric random branch length). Comparisons between hypothesized alignments and true alignments enabled determination of two measures of alignment accuracy, that of the total data set and that of individual branches. In general, our results indicate that as alignment error increases, topological accuracy decreases. This trend was much more pronounced for data sets derived from more pectinate topologies. In contrast, for balanced, ultrametric, equal branch length tree shapes, alignment inaccuracy had little average effect on tree reconstruction. These conclusions are based on average trends of many analyses under different conditions, and any one specific analysis, independent of the alignment accuracy, may recover very accurate or inaccurate topologies. Maximum likelihood and Bayesian, in general, outperformed neighbor joining and maximum parsimony in terms of tree reconstruction accuracy. Results also indicated that as the length of the branch and of the neighboring branches increase, alignment accuracy decreases, and the length of the neighboring branches is the major factor in topological accuracy. Thus, multiple-sequence alignment can be an important factor in downstream effects on topological reconstruction.

Base Sequence↗

PubMedDate not supplied

Screening for speech and language disorders: the reliability, validity and accuracy of the General Language Screen.

This paper reports the reliability, validity and accuracy of the General Language Screen (GLS) as the first stage in its development as a potential screening instrument for the identification of speech and language disorder (SLD) in the primary care setting. Data reported were obtained during the Cambridge Language and Speech Project (CLASP) a longitudinal epidemiological study of primary SLD. The GLS was originally used in initial CLASP sample ascertainment when children were aged 36 months. This report utilises speech and language data collected at subsequent stages of this study (37-months, 45-months and 8-years) to determine the reliability, validity and accuracy of the GLS. The GLS demonstrated sufficient levels of reliability (internal consistency alpha = 0.74) and validity (criterion validity r = -0.55). Adequate construct validity was demonstrated by a factor analysis in which two language related factors were identified. These data therefore justified exploration of the accuracy of the GLS as a screening instrument. Analysis of accuracy in this context is complicated by lack of a generally accepted method of defining SLD case status. This report utilises data on language function at different stages of development to provide measures of GLS accuracy over time. Concurrent accuracy, measured against parental report of language function at 37-months, was good (ROC area under the curve = 0.93). Predictive accuracy measured against direct assessment of speech and language at 45-months and 8-years was, as expected, somewhat less (ROC = 0.77 and 0.68 respectively). The implications for the use of the GLS as a screening instrument are discussed. The data indicate that the GLS would function most usefully as the first stage of a two-stage screen for SLD in the primary care setting. Recommendations are made as to the nature of the second stage of such a screen and plans for future research are outlined.

Child↗

PubMed2002

Evaluating the accuracy of technicians and pharmacists in checking unit dose medication cassettes.

The accuracy rates of board-registered pharmacy technicians and pharmacists in checking unit dose medication cassettes in the inpatient setting at two separate institutions were examined. Cedars-Sinai Medical Center and Long Beach Memorial Medical Center, both in Los Angeles county, petitioned the California State Board of Pharmacy to approve a waiver of the California Code of Regulations to conduct an experimental program to compare the accuracy of unit dose medication cassettes checked by pharmacists with that of cassettes checked by trained, certified pharmacy technicians. The study consisted of three parts: assessing pharmacist baseline checking accuracy (Phase I), developing a technician-training program and certifying technicians who completed the didactic and practical training (Phase II), and evaluating the accuracy of certified technicians checking unit dose medication cassettes as a daily function (Phase III). Twenty-nine pharmacists and 41 technicians (3 of whom were pharmacy interns) participated in the study. Of the technicians, all 41 successfully completed the didactic and practical training, 39 successfully completed the audits and became certified checkers, and 2 (including 1 of the interns) did not complete the certification audits because they were reassigned to another work area or had resigned. In Phase II, the observed accuracy rate and its lower confidence limit exceeded the predetermined minimum requirement of 99.8% for a certified checker. The mean accuracy rates for technicians were identical at the two institutions (p = 1.0). The difference in mean accuracy rates between pharmacists (99.52%; 95% confidence interval [CI] 99.44-99.58%) and technicians, (99.89%; 95% CI 99.87-99.90%) was significant (p < 0.0001). Inpatient technicians who had been trained and certified in a closely supervised program that incorporated quality assurance mechanisms could safely and accurately check unit dose medication cassettes filled by other technicians.

Drug Packaging↗

PubMed2004

The accuracy of extended histopathology to detect immunotoxic chemicals.

The accuracy of extended histopathology to detect immunotoxic chemicals in female B6C3F1 mice was evaluated under the auspices of the National Toxicology Program (NTP). A workgroup was formed consisting of four pathologists who conducted extended histopathological evaluation of lymphoid tissues obtained from a subset of NTP toxicology studies, in which previously detailed immunotoxicity assessment was performed. In addition, a positive control data set of three known immunosuppressive agents, one negative control data set, and an additional negative control group composed of the vehicle only treated groups were included. Data obtained from extended histopathology evaluations were compared to more traditional immune test results (both functional and nonfunctional) from previously conducted immunotoxicity assessments. Analyses of the data indicated that the ability to identify immunotoxic chemicals using histological endpoints decreased linearly as the level of stringency used to determine significant histopathological changes increased. A relatively high (80%) accuracy level was achieved when histological changes were considered in toto (i.e., any histological abnormality in the three tissues examined), using minimal or mild criteria for scoring. When minimal or mild histological changes were considered significant for a specific tissue, a 60% level of accuracy in identifying immunotoxic chemicals was obtained as compared to a 90% accuracy level that was achieved with this data set using the antibody plaque forming cell response, considered to represent the most predictive functional test. A minimal classification was obtained in the analyses of the negative control groups, suggesting that use of the minimal classification for hazard identification is inappropriate as it will likely result in a high incidence of false positives. This was not the case when mild classifications were used as an indicator of significance, which in most instances allowed the successful identification of negatives. When moderate to marked histopathological changes were used to identify immunotoxic chemicals, the level of accuracy that could be achieved was poor. A considerably higher level of accuracy was obtained for the positive control data set than the test chemical data set suggesting that the ability to detect an immunotoxic agent histologically is proportional to the potency of the immunotoxic agent. Comparison of immune function test results and histopathological results obtained from the high-dose treatment groups and the lower-dose treatment group did not reveal any significant differences between the two endpoints to predict immunotoxicity as a function of dose. Of the three lymphoid organs examined, (i.e., lymph node, thymus, and spleen), the most consistent and discernible histological lesions were observed in the thymus cortical region. These lesions correlated with thymus: body weight ratios and to a slightly lesser extent, the antibody plaque forming cell response. Addition of general toxicological endpoints such as body weight and leukocyte counts did not significantly improve the sensitivity of extended histopathology for this data set. Taken together, these data suggest that, while not as sensitive as functional analyses, extended histopathology may provide a reasonable level of accuracy as a screening test to identify immunotoxic chemicals, provided the level of stringency used to score histological lesions is carefully considered to allow for detection of immunotoxic agents while limiting false positives.

Animals↗

PubMed1993

In vivo kinematics of the cervical spine. Part I: Development of a roentgen stereophotogrammetric technique using metallic markers and assessment of its accuracy.

A technique for simultaneous roentgen stereophotogrammetry (RS) was developed, and its accuracy was assessed. In vitro models fabricated from dried cadaveric C4 and C5 vertebrae were used to simulate the motion behavior of the cervical spine. Metallic markers made of Vitallium beads (diameter < 0.3 mm) were implanted into the posterior and anterior surfaces of each vertebra at surgically accessible locations to simulate the bead placement for both posterior and anterior surgical approaches to the cervical spine. A series of roentgen stereo pairs were obtained to systematically assess the accuracy (validity) of displacement measurements in anteroposterior (AP) translation, axial rotation, and flexion/extension. In addition, the effects of soft tissue density on the accuracy of the system were investigated by obtaining a series of roentgen stereo pairs with the experimental model immersed in a water bath. The coordinates of the metallic markers on the radiographs were then digitized by two raters who were not informed of the actual motion (i.e., blind study). The results indicated a high accuracy throughout the study. Overall root mean square errors were 0.07 mm for AP translation, 0.08 degrees for axial rotation, and 0.14 degrees for flexion/extension. The corresponding accuracy estimates (R2 values by linear regression analysis) were very high (0.992, 0.998, and 0.995) when the measurement results were compared with the actual displacements. The water bath did not affect measurement accuracy, indicating that soft tissue density should have little effect on the accuracy of the technique for in vivo applications. This system appears to be an accurate and reliable method for assessment of simulated in vivo cervical spine motion, regardless of the rater. The technique has been further used in in vivo assessment of cervical spine kinematics in one patient to confirm the efficacy of the developed technique.

Atlanto-Axial Joint↗

PubMed1999

Precision and accuracy of the measurement of antiepileptic drugs in South Africa.

The accuracy and the precision with which a drug concentration is quantified in the blood has a significant impact on the therapeutic drug monitoring (TDM) of the drug. In the absence of a system of accreditation of laboratories in South Africa, this study was designed to compare the accuracy and the precision of the measurement of antiepileptic drugs by 24 South African laboratories with those of non-South African laboratories that participate in the United Kingdom National External Quality Assessment Scheme (UKNEQAS). Three test samples, containing a range of concentrations of phenytoin, valproate, carbamazepine, and phenobarbitone spiked into newborn calf serum were distributed to participating laboratories, which were asked to measure the serum concentrations using their routine assay method. Coefficients of variation were used to assess precision of measurements, and the percentage difference of the consensus mean from the spike value was used as an assessment of accuracy. There was comparable precision in the measurements for both the South African and the non-South African groups. However, there appeared to be a difference in the accuracy of measurement between the two groups. It was noted that the majority (77%) of the South African laboratories used the Abbott fluorescence polarization immunoassay (FPIA) with TDx analyzers (Abbott Laboratories, Abbott Park, IL, USA). Further analysis of the results of the South African and UKNEQAS subgroups using the FPIA technique showed a reduction in statistic bias, suggesting that part of the explanation for the statistic difference in the accuracy may be an intertechnique bias related to the use of a nonhuman matrix for sample preparation. Additional studies are required to determine other causes for the statistic differences in accuracy. However, the differences in accuracy are unlikely to be of clinical significance.

Animals↗

PubMed2004

Accuracy of urinalysis dipstick techniques in predicting significant proteinuria in pregnancy.

OBJECTIVE: To estimate the accuracy of point-of-care dipstick urinalysis in predicting significant proteinuria in pregnancy. DATA SOURCES: Literature from 1970 to February 2002 was identified via 1). general bibliographic databases, that is, MEDLINE and EMBASE, 2). Cochrane Library and relevant specialist register of the Cochrane Collaboration, and 3). checking the reference lists of known primary and review articles. METHODS OF STUDY SELECTION: Studies were selected if the accuracy of dipstick urinalysis techniques in predicting total protein excretion was estimated compared with a reference standard (laboratory estimation of protein excretion). The tests included visually read color-change dipsticks and automated dipstick urinalysis. Study selection, quality assessment, and data abstraction were performed independently and in duplicate. TABULATION, INTEGRATION, AND RESULTS: Data from selected studies were abstracted as 2 x 2 tables comparing the test result with the reference standard. Test accuracy was expressed as likelihood ratios. Summary likelihood ratios were generated as measures of diagnostic accuracy to determine posttest probabilities. The electronic search produced 1543 citations. After independent review of published articles, a total of 34 articles was obtained for further scrutiny, and 7 studies were considered eligible for inclusion in the review. The 6 studies evaluating visual dipstick urinalysis produced a pooled positive likelihood ratio of 3.48 (95% confidence interval 1.66, 7.27) and a pooled negative likelihood ratio of 0.6 (95% confidence interval 0.45, 0.8) for predicting 300 mg/24-hour proteinuria at the 1+ or greater threshold. CONCLUSION: The accuracy of dipstick urinalysis with a 1+ threshold in the prediction of significant proteinuria is poor and therefore of limited usefulness to the clinician. Accuracy may be improved at higher thresholds (greater than 1+ proteinuria), but available data are sparse and of poor methodological quality. Therefore, it is not possible to make meaningful inferences about accuracy at higher urine dipstick thresholds. There is an urgent need for research in this area of common obstetric practice.

Female↗