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Biomedical subjects

L Irwig

Publications and source records attributed to L Irwig.

At least 37 records · Page 2Linked to original sources
PubMed2000

How accurate is dimercaptosuccinic acid scintigraphy for the diagnosis of acute pyelonephritis? A meta-analysis of experimental studies.

UNLABELLED: The purpose of this study was to evaluate the performance of dimercaptosuccinic acid (DMSA) scintigraphy in the diagnosis of acute pyelonephritis and to compare the test performance of the standard technique, planar DMSA, with the newly introduced technique, SPECT DMSA. METHODS: All published animal studies in which DMSA scintigraphy was compared with histopathology, the reference standard for acute pyelonephritis, were identified using a comprehensive search strategy with the MEDLINE and EMBASE databases. Test performances of all DMSA methods and SPECT versus planar DMSA were analyzed using summary receiver operating characteristic (sROC) curves. RESULTS: Seven studies were identified, including 2 of SPECT DMSA. Problems in study design or reporting were common, with numerical errors in 4 studies. Overall, at a sensitivity of 86%, specificity was estimated to be 91%. Detection of acute pyelonephritis was at a lower threshold for SPECT than for planar DMSA (sensitivity/specificity values of 97%0/66% compared with 82%/ 97%), and the overall test performance of SPECT was not demonstrably better than that of planar DMSA. When applied to a group of children with a prevalence of renal damage of 40%, this means that 98% of children with abnormal planar DMSA scans will have renal damage, whereas only 65% of those with abnormal SPECT scans will have renal damage. Planar and SPECT DMSA will miss 11% and 3% of children with renal damage, respectively. Out of 100 children in the hypothetical group with 40% experiencing renal damage, SPECT will identify 6 extra true cases of renal damage at the expense of 19 extra false positives, when compared with planar DMSA. CONCLUSION: Published studies of DMSA test performance are few in number and have significant methodologic problems that should be avoided in future studies. DMSA, particularly the planar technique, performs well for the diagnosis of acute pyelonephritis. Using test performance criteria, SPECT DMSA alone has not been shown to be preferable to the established planar method and will result in a small number of true-positives at the expense of a larger number of false-positives.

Acute Disease↗
PubMed2000

Should we use carbohydrate-deficient transferrin instead of gamma-glutamyltransferase for detecting problem drinkers? A systematic review and metaanalysis.

BACKGROUND: Carbohydrate-deficient transferrin (CDT) has been used as a test for excessive alcohol consumption in research, clinical, and medico-legal settings, but there remain conflicting data on its accuracy, with sensitivities ranging from <20% to 100%. We examined evidence of its benefit over a conventional and less expensive test, gamma-glutamyltransferase (GGT), and compared the accuracy of different CDT assay methods. METHODS: We performed a systematic review using summary ROC analysis of 110 studies prior to June 1998 on the use of CDT in the detection of alcohol dependence or hazardous/harmful alcohol use. RESULTS: We identified several potential sources of bias in studies. In studies examining CDT and GGT in the same subjects, subject characteristics were less likely to influence the comparison. In such paired studies, the original Pharmacia CDT assay was significantly more accurate than GGT, but the modified CDTect assay did not perform as well as the original and was not significantly better than GGT. The accuracy of the AXIS %CDT assay was statistically indistinguishable from modified CDTect. Several CDT assay methods appeared promising, in particular, liquid chromatography (chromatofocusing, HPLC, fast protein liquid chromatography) and isoelectric focusing, but there were insufficient paired studies from which to draw firm conclusions. CONCLUSIONS: In studies published before June 1998, the results obtained with commercially available CDT assays were not significantly better than GGT as markers of excessive alcohol use in paired studies. Further high-quality studies comparing CDTect (modified) and other CDT assays with GGT in the same subjects are needed.

Age Factors↗
PubMed1999

Meta-analysis of diagnostic tests with imperfect reference standards.

We present a method to estimate the summary receiver operating characteristic (SROC) curve for combining information on a diagnostic test from several different studies. Unlike previous methods that assume the reference standard to be error free, our approach allows for the possibility of errors in the reference standard, through use of a latent class model. The model provides estimates of the sensitivity and specificity of the diagnostic test and the case prevalence in each study; these parameters can then be used in a meta-analysis, for example, using the regression method proposed by Moses et al., of a measure of test discrimination on a measure of the diagnostic threshold, to fit the SROC. The method is illustrated with an example on Pap smears that shows how adjusting for imperfection in the reference standard typically reduces the scatter of data in the SROC plot, and tends to indicate better performance of the test than otherwise.

Algorithms↗
PubMed1999

Randomized double-blind trial of beta-carotene and vitamin C in women with minor cervical abnormalities.

A double-blind, placebo-controlled, randomized, factorial study using a daily oral administration of 30 mg beta-carotene and/or 500 mg vitamin C was conducted in 141 women with colposcopically and histologically confirmed minor squamous atypia or cervical intra-epithelial neoplasia (CIN) I. Over approximately 2 years of follow-up, 43 lesions regressed to normal and 13 progressed to CIN II. The regression rate was slightly higher, but not significantly so, in those randomized to beta-carotene compared to no beta-carotene (hazard ratio = 1.58, 95% CI: 0.86-2.93, P = 0.14) and slightly lower, but not statistically significant, for those randomized to vitamin C compared to no vitamin C (hazard ratio = 0.65, 95% CI: 0.35-1.21, P = 0.17). In a model with no interaction, the progression rate was slightly higher in those randomized to beta-carotene (hazard ratio = 1.75, 95% CI: 0.57-5.36, P = 0.32) and also in those randomized to vitamin C (hazard ratio = 2.40, 95% CI: 0.74-7.80, P = 0.13). Neither of these were statistically significant. However, there was some evidence of an interaction effect of the two compounds on the progression rate (P = 0.052), with seven of the progressed lesions occurring in those randomized to both vitamins compared to a total of six in the three other groups. The currently available evidence from this and other trials suggests that high doses of these compounds are unlikely to increase the regression or decrease the progression of minor atypia and CIN I.

Adult↗
PubMed1998

Staff attitudes and retention of patients in methadone maintenance programs.

A study was made of the effect of staff commitment to abstinence-oriented policies on retention of patients in methadone maintenance. Staff working in six public methadone programs in Sydney, Australia, were surveyed in 1989 and 1992 using the Abstinence Orientation Scale. The association of the clinics' median Abstinence Orientation scores with the time in treatment of a random sample of their 1988-1989 admissions was summarised using Cox regression. Patients' risk of discharge increased by a factor of three with every one unit increase in the clinics' median Abstinence Orientation scores, (RR 3.4, 95% CI 2.3-5.0). Abstinence-oriented policies were shown to disadvantage ex-prisoners.

Adult↗
PubMed1998

A systematic review of the effects of screening for colorectal cancer using the faecal occult blood test, hemoccult.

OBJECTIVE: To review effectiveness of screening for colorectal cancer with faecal occult blood test, Hemoccult, and to consider benefits and harms of screening. DESIGN: Systematic review of trials of Hemoccult screening, with meta-analysis of results from the randomised controlled trials. SUBJECTS: Four randomised controlled trials and two non-randomised trials of about 330 000 and 113 000 people respectively aged >=40 years in five countries. MAIN OUTCOME MEASURES: Meta-analysis of effects of screening on mortality from colorectal cancer. RESULTS: Quality of trial design was generally high, and screening resulted in a favourable shift in the stage distribution of colorectal cancers in the screening groups. Meta-analysis of mortality results from the four randomised controlled trials showed that those allocated to screening had a reduction in mortality from colorectal cancer of 16% (relative risk 0.84 (95% confidence interval 0.77 to 0.93)). When adjusted for attendance for screening, this reduction was 23% (relative risk 0.77 (0.57 to 0.89)) for people actually screened. If a biennial Hemoccult screening programme were offered to 10 000 people and about two thirds attended for at least one Hemoccult test, 8.5 (3.6 to 13.5) deaths from colorectal cancer would be prevented over a period of 10 years. CONCLUSION: Although benefits of screening are likely to outweigh harms for populations at high risk of colorectal cancer, more information is needed about the harmful effects of screening, the community's responses to screening, and costs of screening for different healthcare systems before widespread screening can be recommended.

Adult↗
PubMed1998

Changing attitudes and beliefs of staff working in methadone maintenance programs.

Starting in 1989, an attempt was made to change the aim of methadone treatment in NSW from abstinence to harm-minimisation. A study was undertaken to measure change in attitudes among staff working in public methadone programs in Sydney. Using scales developed in a 1989 survey, we found a statistically significant and meaningful reduction in support for abstinence-oriented policies had occurred by 1992. There was no change in staff's support for the punishment of illicit drug use or their knowledge of the risks and benefits of methadone maintenance. This suggests problems with staff attitudes and, indirectly, the effectiveness of public health interventions, can be addressed using educational campaigns.

Attitude of Health Personnel↗
PubMed1998

Biochemical markers of acute myocardial infarction: strategies for improving their clinical usefulness.

We investigated the early diagnostic utility, including incremental value, of the serum cardiac markers creatine kinase (CK), CK-MB (mass and activity measurements), cardiac troponin T, and myoglobin in the diagnosis of acute myocardial infarction (AMI) in patients presenting to a major teaching hospital with chest pain and non-diagnostic electrocardiographs (ECG). The reference diagnosis of acute myocardial infarction was made by a single, independent cardiologist using World Health Organization criteria. CK and CK-MB mass were the only significant predictors of AMI at presentation to the Emergency Department. Logistic regression analysis revealed that CK did not significantly predict (P = 0.23) myocardial infarction once CK-MB mass was in the model. Using test results on follow up, in addition to presentation CK-MB mass, change in CK-MB mass was the only other significant independent predictor of AMI. Likelihood ratios for various levels of the significant markers in the logistic regression are given. In conclusion, CK-MB mass measurement was the only useful serum cardiac marker for the diagnosis of AMI in patients presenting with chest pain with non-diagnostic ECGs.

Biomarkers↗
PubMed1998

A flow diagram to facilitate selection of interventions and research for health care.

Decisions about health care should be informed by systematic review of valid research evidence on the effects of interventions on health outcomes that matter. If systematic review suggests it is likely that a health care intervention does more good than harm in some settings, questions must be addressed about the local applicability of the intervention, its cost-effectiveness, and feasibility of implementation. If systematic review suggests that it is unlikely that an intervention does more good than harm in any setting, its use should be discouraged, while existing interventions are improved or alternative interventions developed. If it is uncertain whether an intervention does more good than harm, further analysis of existing data or new controlled trials are required. The article contains a flow diagram, which provides a structure for making such decisions.

Cost-Benefit Analysis↗
PubMed1997

Comparing dichotomous screening tests when individuals negative on both tests are not verified.

Two dichotomous screening tests are often compared by performing both tests in a sampled population, and submitting positive results on either test to verification by the reference standard. Unbiased estimates of the true positive and false positive rates of each test cannot be estimated directly. However, unbiased estimates of the relative true positive and relative false positive rates may be obtained. When one test has a higher true positive rate at the expense of a higher false positive rate, the trade-off is represented by the ratio of extra false positives detected to extra true positives detected. A 95% confidence interval for this ratio is derived. This ratio is prevalence dependent and only applies to the sampled population. For target populations of different prevalence, estimates of the ratio may be obtained if one of the following applies: (i) the test characteristics of one test are known; (ii) the relative prevalence is known; and (iii) certain assumptions are made.

Data Interpretation, Statistical↗
PubMed1997

The quality and interpretation of mammographic screening trials for women ages 40-49.

Using MEDLINE and the bibliographies of retrieved articles and reviews, we identified and systematically reviewed the quality and results of all randomized trials of mammographic screening that included women less than 50 years of age. Eight randomized trials were identified, 7 of which included women less than 50. Identified trials were assessed for the following design features: (a) method of randomization, (b) documented comparability of baseline data, (c) standardized criteria for breast cancer death, (d) blinded review of cause of death, (e) completeness of follow-up, and (f) use of an "intention to treat analysis." The quality of trials was generally high, with a total of almost 160,000 women randomized. In women aged 40-49 at entry, the overall, absolute risk difference between those invited and those not was 0.0004 (95% CI: 0 to 0.0009). Yet, what does this mean to a 40-year-old women considering screening? If 10,000 women aged 40-49 years were screened regularly, then after a decade there would be about 4 less breast cancer deaths? Is that worthwhile? This is a difficult question, and it needs to be weighed against the problems arising from false positives and ductal carcinoma in situ. We recommend that women in this age group intending to be screened should be fully informed of these results in terms of absolute benefit.

Adult↗
PubMed1997

Quality of life after breast conservation or mastectomy: a systematic review.

BACKGROUND: For early breast cancer, survival after breast conservation is similar to that after mastectomy. Some women may not have a clear preference and wish to have further information about quality of life experienced after the alternative treatments. This paper describes a systematic review of randomized trials on mastectomy versus breast conservation for which there are data on quality of life or psychosocial outcomes. METHODS: Literature was reviewed to find all randomized controlled trials comparing breast conservation to mastectomy, with quality of life or psychological effects as an outcome. Studies were then critically appraised by two reviewers independently and any disagreements about their quality and results resolved by discussion. RESULTS: A total of six randomized trials met our inclusion criteria. In general, they are of poor quality. Women who had breast conservation had a more favourable body image of themselves than those who had mastectomy in all five studies in which it was examined. The evidence was statistically inconclusive for all the other dimensions measured, namely perceptions of psychological health, sexual health, physical health, fear of the future and global quality of life. Radiotherapy may be a determinant of poorer psychological health and body image. CONCLUSIONS: Apart from body image, it is unclear whether breast conservation or mastectomy results in better psychosocial outcomes. Moreover, the studies were done before evidence was available to inform women about the equivalence of survival with these alternative treatments. Therefore there is inadequate information available to help many women decide about their choice of treatment in the future. Preference trials should be conducted, using standardized quality-of-life measures, in which women who are uncertain about which treatment to choose are randomized to breast conservation or mastectomy.

Breast Neoplasms↗
PubMed1997

Measuring and comparing the attitudes and beliefs of staff working in New York methadone maintenance clinics.

Scales measuring commitment to abstinence-oriented policies, attitudes to drug addiction, and knowledge of methadone maintenance were refined and tested in a survey of staff working in 14 New York maintenance programs. Confirmatory factor analysis established the validity of a 9-item Abstinence Orientation Scale and a 6-item Disapproval of Drug Use Scale. Scores on the two scales and Knowledge scores were highly correlated. There were highly significant differences in the mean Abstinence Orientation scores of the administrative and better qualified clinical staff on the one hand and the less qualified staff on the other. Senior staff generally rejected abstinence-oriented policies while nurses and counselors tended to support them.

Adult↗