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Biomedical subjects

B C Choi

Publications and source records attributed to B C Choi.

At least 55 records · Page 3Linked to original sources
PubMed1994

Cell type identification in leukemia: the level of agreement among four independent diagnostic methods.

The level of agreement among four independent diagnostic methods for cell-type identification in leukemia was examined. The four diagnostic methods were routine morphology, electron microscopy, cell surface marker analysis by flow cytometry, and cancer cytogenetics. Sixty-five blood and bone marrow samples from fifty-seven patients were independently investigated by the four methods. It was found that when all cell-type categories were taken into consideration, overall percentages of agreement for pairs of the four diagnostic methods were poor, ranging from 43% to 67%. The kappa statistics, which correct for the agreement expected by chance, were also calculated. These kappa statistics had a range from 0.17 to 0.40 when all cell-type categories were taken into consideration, again indicating poor agreement between the methods pairwise. When each cell type was considered separately, much of the observed agreement was found to be expected on the basis of chance, as indicated by many of the kappa statistics being 0.00. For all categories, overall agreement for all four methods was poor and statistically significant, after correcting for chance (kappa = 0.20, (p = 0.000046). The poor agreement found among the four diagnostic methods indicates the need for further validation studies.

Cytodiagnosis↗
PubMed1993

Use of surnames to identify individuals of Chinese ancestry.

The objectives of this study were to develop and test surname lists for identifying Chinese ancestry. The Ontario all-cause mortality database for the period 1982-1989 was randomly split into source and test data sets. Frequencies by birthplace were compiled for each surname in the source data set, by sex, and the surnames were weighted based on their positive likelihood ratios. Lists of Chinese surnames were then assembled based on varying cutoff levels, and screening performance indicators for each list were calculated, including sensitivity, specificity, positive and negative predictive values, post-test odds, positive likelihood ratio, and yield. The internally generated lists were evaluated in the test data set. Results indicated that surnames have a good potential to identify individuals of Chinese origin. In the source data set, at a cutoff level of 100 for males (217 surnames) and females (210 surnames), both sensitivity and the positive predictive value of the surname lists for males and females were very high, above 80%, and the positive likelihood ratio was above 600. In the test data set and using the same surname lists, the sensitivity, positive predictive value, and positive likelihood ratio remained at a high level: 73%, 81%, and 603, respectively, for males; and 73%, 84%, and 772, respectively, for females. Various scenarios and their methodological implications are discussed.

China↗
PubMed1993

Characterization of a peroxidase in excretory-secretory product of adult Paragonimus westermani.

When activity of peroxidase in adult Paragonimus westermani was monitored using o-dianisidine and H2O2 as substrates, its specific activity was 1.5 times higher in excretory-secretory product (ESP) than in crude extract. The enzyme was purified by two purification steps of Sephacryl S-300 Superfine gel permeation and DEAE-Trisacryl M anion exchange chromatographies. Its activity increased 16.9 fold with 32.3% recovery. The enzyme was inhibited totally by 1 millimoles of dithiothreitol (DTT), 2-mercaptoethanol and azide. Molecular mass was 16 kDa in reducing SDS-polyacrylamide gel electrophoresis (PAGE) or 19 kDa in TSK-Blue gel filtration high performance liquid chromatography (HPLC), respectively. Special staining for peroxidase by diaminobenzidine on SDS-PAGE confirmed the activity. The peroxidase was less reactive to a paragonimiasis serum when observed by SDS-PAGE/immunoblot. In addition, specific activities of superoxide dismutase (SOD) and catalase were also identified in the ESP. High activities of these antioxidant enzymes in ESP indicate that they are parts of defense mechanisms against reactive oxygen intermediates from host.

Animals↗
PubMed1992

Antibody drug carrier for immunotherapy of superficial bladder cancer: ultrastructural studies.

Superficial bladder cancer represents a promising target for intravesical, antibody-guided therapy. The construction of an optimum antibody-cytotoxic drug conjugate depends mostly on the appropriate selection of a monoclonal antibody (mAb). We have used immunogold labeling and SEM to specifically map the distribution of antigens expressed on three bladder cancer cell lines and on the luminal surface of biopsies from human transitional cell carcinoma of various grades and from normal bladder mucosa. The 48-127 mAb, which recognizes a M(r) 54,000 surface glycoprotein (gp54), was found to be very promising as a potential drug carrier. This antibody reacts with the surface of cells from low- and high-grade tumors; it does not react with the normal urothelium. Labeling of normal bladder mucosa was observed, however, on microvillous intermediate urothelial cells occasionally exposed by small areas of desquamation. The 48-127 mAb could target drugs to all areas of transformed urothelium while avoiding drug delivery to the normal, undesquamated bladder mucosa. Kinetics of gp54/48-127/gold complexes were tested in vitro with T24 and RT4 human bladder carcinoma cell lines incubated in the presence of the 48-127 mAb directly conjugated with 17.7-nm gold particles. Internalization of the gp54/48-127/gold complex was readily demonstrated by transmission electron microscopy. These results suggest that the 48-127 mAb represents a valuable drug carrier for intravesical therapy, allowing specific tumor targeting and internalization of various cytotoxic agents.

Aged↗
PubMed1992

Sensitivity and specificity of a single diagnostic test in the presence of work-up bias.

A diagnostic test is put into routine use by being applied to a population with unknown test status and unknown disease status. All subjects with a positive test are then referred to a "gold standard" assessment for the disease. Subjects with a negative test are normally not referred to the "gold standard" assessment. In some cases, the investigators may refer a small random sample of subjects with a negative test to the "gold standard" assessment in order to determine if they really do not have the disease. If "gold standard" results are not available on an entire population, it is well-known that work-up bias, or sequential-ordering bias, exists. In this situation, classical equations for sensitivity and specificity give biased results. This paper describes an equation for estimation of prevalence, and two new equations which calculate sensitivity and specificity from prevalence and predictive values, and which are appropriate for data from this type of "irregular observational design".

Bias↗
PubMed1992

Classification, direction, and prevention of bias in epidemiologic research.

We describe an extension of an existing framework used by several investigators for classifying various types of bias. The framework consists of three categories of bias: selection, information, and confounding. The existing framework is expanded to include subclassification according to the type of study design: cross-sectional, case-control, retrospective cohort, and prospective cohort. Direction and method of prevention of biases within each category in the framework are discussed. This article provides a useful checklist for epidemiologists to determine possible sources and methods of reduction of bias that are specific to a particular type of study design.

Bias↗
PubMed1992

Definition, sources, magnitude, effect modifiers, and strategies of reduction of the healthy worker effect.

This article summarizes, compares, and contrasts the definition, sources, magnitude, effect modifiers, and strategies of reduction of the healthy worker effect (HWE), based on the opinion expressed in the papers of nine contributors who responded to the request of the Industrial Disease Standards Panel (IDSP), Ontario, Canada. It provides an insight into the complex issues relating to the HWE. In addition, the catalog of 15 strategies to reduce the HWE is deemed to be useful for investigators in occupational epidemiology.

Age Factors↗
PubMed1991

Mass screening for rectal neoplasm in Jiashan County, China.

Jiashan county is a rural area in China with very high incidence and mortality rates of colorectal cancer. From 1980 to 1984, we conducted a mass screening for rectal neoplasm in the 11 people's communes in this county. Of the 72,879 individuals who were eligible for screening, 60,496 participated, representing an overall participation rate of 83.0%. Both the fecal occult blood (OB) test and rectoscopy were performed on 47,560 of the participants, and rectoscopy only was performed on the remaining 12,936 individuals. From the mass screening, 15 rectal cancers, 3 carcinoids, 899 polyps, 98 ulcers, and 7 inflammatory tumors were detected, a total of 1022 cases. Eight of the 15 detected cases of rectal cancer were in Dukes' stage A. We did not find any evidence for an association between schistosomiasis and colorectal cancer. Results from the OB test were found to have a negative correlation with results from rectoscopy (odds ratio = 0.8, 95% CI = 0.6, 1.1). The OB test had a high false positive rate of 32.7%, and a poor positive predictive value of 3.5%. Both its positive and negative predictive powers were below 1.0, in other words, its positive likelihood ratio was below 1.0 and negative likelihood ratio was above 1.0, indicating that the OB test is not informative and has a poor predictive accuracy for rectal neoplasm. In addition, there were a number of practical problems concerning the use of the OB test for mass screening in the rural community.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

A proportionate mortality study on risk of bladder cancer among rubber workers.

A proportionate mortality study was based on a sample of 6208 workers who were employed for at least 4 months during the period from 1917 to 1983 in a rubber tire manufacturing plant in Ontario, Canada. Identifying information of the workers was extracted from company records and linked to the Ontario Cancer Registry 1964-1983 death files. Among the cohort, 153 cancer deaths (146 male, 7 female), which included 6 bladder cancer deaths (all male), were found. For the six bladder cancer deaths, average age at time of first employment was 33.5 years, and average time from first employment to time of death was 31.8 years (with a range from 25.3 to 38.3 years). Proportionate mortality ratio (PMR) and mortality odds ratio (MOR), and their standardized forms (SPMR and SMOR), were calculated using the general population in Ontario for comparison. PMR and MOR were found to be 1.44 and 1.45, respectively. When the Ontario proportionate cancer mortality was applied to the cohort, adjusted for age and sex, 4.69 bladder cancer deaths were expected. The six bladder cancer deaths among the rubber workers therefore represented a 1.28-fold increase in standardized proportionate bladder cancer mortality when compared to the general population. Age and sex adjusted SMOR was found to be 1.29.

Carcinogens↗
PubMed1990

Gene delivery to glioma cells in rat brain by grafting of a retrovirus packaging cell line.

Retrovirus vectors only integrate into the genome of dividing cells and can thus be used to selectively infect tumor cells in the adult rat brain. Gene delivery was assessed by using the retrovirus BAG vector, which bears the Escherichia coli lacZ gene under the MoMLV LTR promoter-enhancer element, and by histochemical staining for bacterial beta-galactosidase activity. Direct injection of this vector (90-900 cfu) into the adult rat brain, with or without prior inoculation of C6 glioma cells (2 x 10(5) cells) resulted in labeling of only a few cells as assessed 1 week later. When the psi 2-BAG packaging line was grafted into the brain, labeled psi 2-BAG cells could be found after 1 day, but not after 5 days, following grafting, suggesting that the grafted cells had been rejected and that no endogenous cells had integrated released vector, or that expression of lacZ had been turned off. In contrast, when the psi 2-BAG packaging line was grafted into a brain region, which had been inoculated previously with rat C6 glioma cells (2 x 10(5) cells), beta-galactosidase labeling of these tumor cells, identified by immunocytochemistry for glial fibrillary acidic protein and S100, could be demonstrated 10 days later. Thus, grafting of retrovirus packaging lines into adult brain provides a mean to infect tumor cells in situ. The grafted packaging cells may continue to release retrovirus particles for an extended period, thus infecting more cells at the stage of division appropriate for viral integration, as compared to inoculation of the virus alone. Grafting of retrovirus packaging cell lines could be used to selectively deliver "killer" or "suppressor" genes to tumor cells in the brain to curtail their growth.

Animals↗
PubMed1990

Microscopic haematuria as a predictor of urological diseases among steel workers.

A cohort of 501 workers in a steel mill in Ontario, Canada was followed up from 1974 to 1986 for 13 years. Results indicate that the 13-year cumulative incidence of urological diseases among workers who had a positive urinalysis result of microscopic haematuria at the beginning of the follow-up period (1974) was 1.3 times that of those who had a negative urinalysis result (95% confidence interval 0.6-2.8). This relative risk remained the same after adjusting for age and smoking. This indicates that there is a possibility that urinary screening for microscopic haematuria could be a useful predictor of urological disease occurrence. However, the benefits of early detection and management were difficult to demonstrate. Serious urological diseases, particularly urinary cancers, were not detected earlier as a result of the urinary screening test in this study. Several studies have been done to validate the test in the past. More work to validate the test and to determine the predictive accuracy is recommended.

Adult↗
PubMed1990

Effects of mailing strategies on response rate, response time, and cost in a questionnaire study among nurses.

We conducted a pilot study to determine the most efficient mailing strategy for a postal questionnaire study among nurses in Ontario, Canada. Five mailing strategies involving types of stamps on the return envelopes were considered: no stamp, business-reply stamp, metered stamp, small regular stamp, and large commemorative stamp. We found that paper stamps, especially large commemorative stamps, on return envelopes increased the response rate and reduced the response time, as compared with other mailing strategies. Business-reply stamps had the lowest cost per response received and a low total cost.

Evaluation Studies as Topic↗
PubMed1989

An exploratory case-control study of brain tumors in children.

An exploratory case-control study of childhood brain tumors was conducted in southern Ontario between 1977 and 1983, on 74 cases and 138 age- and sex-matched population controls. A significantly elevated risk (perhaps due to early case symptoms) was seen for skull X-rays at least 5 years prior to diagnosis, and for head or neck injuries which required medical attention. However, no evidence of an increased risk appeared for exposure to sick pets or to pesticides, maternal or paternal history of smoking, and various birth characteristics or antenatal exposure of the child, though these have previously been reported to be associated with childhood brain tumors. With respect to the hypothesis that N-nitroso compounds may be involved in the etiology of childhood brain tumors, most exposures of this type were not associated with risk, though a significant positive association was seen for consumption of beer by the mother during pregnancy, and a significant negative association was seen with consumption of fruit juice by the child. Other findings in the present study include an association with developmental problems relating to height and weight and with certain socioeconomic characteristics of the mother. Further investigation of these results in future studies is warranted.

Adolescent↗
PubMed1989

Smoking, occupational exposure to rubber, and lung cancer.

A cohort of 1624 employees (957 men, 667 women) in a rubber factory in Shanghai have been followed up since 1972 and their 12 year mortality experience is presented. The relative risk of lung cancer for smokers was 8.5 for men and 11.4 for women and for rubber workers exposed to curing agents or talc powder 3.2 for men and 4.6 for women.

China↗
PubMed1987

An exploratory case-control study of brain tumors in adults.

An exploratory study of brain tumors in adults was carried out using 215 cases diagnosed in Southern Ontario between 1979 and 1982, with an individually matched, hospital control series. Significantly elevated risks were observed for reported use of spring water, drinking of wine, and consumption of pickled fish, together with a significant protective effect for the regular consumption of any of several types of fruit. While these factors are consistent with a role for N-nitroso compounds in the etiology of these tumors, for several other factors related to this hypothesis, no association was observed. Occupation in the rubber industry was associated with a significant relative risk of 9.0, though no other occupational associations were seen. Two previously unreported associations were with smoking nonfilter cigarettes with a significant trend and with the use of hair dyes or sprays. The data do not support an association between physical head trauma requiring medical attention and risk of brain tumors and indicate that exposure to ionizing radiation and vinyl chloride monomer does not contribute any appreciable fraction of attributable risk in the population studied. The findings warrant further detailed investigation in future epidemiologic studies.

Adult↗
PubMed1986

Contact dermatitis in hairdressers.

18 cases of hand dermatitis in hairdressers seen over a 5-year period are reviewed. The diagnoses in these patients are discussed with reference to other studies of hand dermatitis in hairdressers. Contact allergy due to paraphenylenediamine and related hair dyes was the presenting complaint in younger hairdressers, while formaldehyde allergy occurred in those who were older. The prognosis in the former group of workers with respect to continued employment in the trade tended to be poorer than the latter. Follow-up revealed that hand dermatitis often resulted in the worker not continuing to work in the hairdressing trade.

Adult↗