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Biomedical subjects

C B Schechter

Publications and source records attributed to C B Schechter.

33 records · Page 2Linked to original sources
PubMed1986

The age threshold for isoniazid chemoprophylaxis. A decision analysis for low-risk tuberculin reactors.

Isoniazid chemoprophylaxis recommendations include its use in persons who have positive tuberculin reactions, but neither recent conversion nor other activation risk factors, only if they are under age 35 years. Above this threshold, the isoniazid hepatitis risk is said to outweigh the benefit of preventing activation. Because this policy is controversial, we performed a decision analysis contrasting those who take with those who decline isoniazid therapy according to three outcome measures: life expectancy, likelihood of illness (isoniazid hepatitis and active tuberculosis), and likelihood of fatal illness. We found no threshold between ages 10 and 80 years by the measures of life expectancy and likelihood of fatal illness; isoniazid benefits outweigh risks for all, though the margin is small for the elderly. A threshold exists only in the likelihood of illness: isoniazid risks outweigh benefits for those aged 50 to 65 years. Only extreme variations of assumptions affect these findings. Chemoprophylaxis recommendations should include low-risk tuberculin reactors over age 35 years.

Adolescent↗
PubMedDate not supplied

BCG vaccination to prevent tuberculosis in health care workers: a decision analysis.

OBJECTIVE: To perform a decision analysis to determine the optimal strategy to prevent tuberculosis (TB) in health care workers with negative tuberculin skin tests. METHODS: We used a Markov model to study the occurrence of events each year and compared BCG vaccination to annual tuberculin testing plus isoniazid (INH) preventive therapy for those who become skin test positive. The outcome measures studied were the number of cases and deaths from TB and BCG and/or INH adverse reactions over 10 years. RESULTS: Annual tuberculin testing decreases the number of TB cases by 9% and BCG vaccination decreases the number by 49%, relative to no prevention intervention. BCG vaccination results in fewer deaths than annual tuberculin testing if the workplace incidence of Mycobacterium tuberculosis infection is greater than 0.06%, BCG vaccination effectiveness exceeds 3%, or the rate of fatal BCG adverse reactions is less than 15 times the rate reported in the literature. CONCLUSIONS: BCG vaccination results in less morbidity and mortality than annual tuberculin skin testing for health care workers in workplaces with documented TB transmission despite comprehensive infection control policies and procedures. Current policy on the prevention of TB among health care workers should be reconsidered.

Antitubercular Agents↗
PubMedDate not supplied

Preventive medicine for HIV-infected patients: an analysis of isoniazid prophylaxis for tuberculin reactors and for anergic patients.

OBJECTIVE: To analyze the policies of isoniazid prophylaxis for human immunodeficiency virus (HIV)-infected tuberculin reactors and for HIV-infected anergic patients with unknown tuberculin status. METHODS: Transition-state model of clinical immune deterioration of HIV-infection over ten years, review of published data, and a survey of AIDS experts. Outcome measures are the numbers of tuberculosis cases and deaths prevented and isoniazid toxicity cases and deaths occurring with prophylaxis. PATIENTS: Hypothetical cohorts of HIV-infected 40-year-olds. RESULTS: Because the tuberculosis activation rate is so high in HIV-infected patients, the benefits of prophylaxis far outweigh the risks of isoniazid toxicity for tuberculin reactors with HIV infection at any stage of immune function: 1,469-2,868 tuberculosis cases and 170-274 deaths are prevented per 10,000 cohort over ten years, depending upon the cohort's initial immune state. The benefits of prophylaxis outweigh the risks of isoniazid toxicity for anergic HIV-infected patients if they come from a community with a 2% to 3% or greater prevalence of Mycobacterium tuberculosis infection. CONCLUSIONS: Isoniazid prophylaxis is a reasonable prevention measure for HIV-infected tuberculin reactors and for many HIV-infected anergic patients.

AIDS-Related Opportunistic Infections↗
PubMedDate not supplied

Evaluation of costs and benefits of advances in cytologic technology. International Academy of Cytology Task Force summary. Diagnostic Cytology Towards the 21st Century: An International Expert Conference and Tutorial.

ISSUES: Uterine cervical cytology smears are among the most cost-effective cancer prevention interventions available, but they are not infallible, and new or modified technologies have been and will be proposed to improve diagnostic accuracy. Before these new technologies are accepted, their performance attributes will be carefully studied and defined. Equally important in this era of fiscal constraints are cost/benefit analyses, for which we review certain guidelines. CONSENSUS POSITION: In an effort to control rising costs in the health care sector, there has been a strong incentive to move toward a market system, and a variety of forces are acting to drive down expenditures. These same pressures will continue to be brought to bear on the providers of cervical cytology services. It must be emphasized that the technical knowledge required to define cost-effective medical practice lies within the medical profession itself, which must recognize the following: (a) Resources are finite; (b) Elimination of fraud, abuse and waste is not enough to bring health care expenditures down to levels considered acceptable to government and business; (c) The medical profession must take the responsibility to identify the health and economic consequences of the services it provides and make wise recommendations for allocation of resources to optimize health consequences. The analysis of costs and benefits must be viewed from a societal perspective and presented in terms of the marginal impact on current practice. This does not mean that new technologies must reduce cost; on the contrary, improvements in health can be expected to come at a price, but at a price commensurate with value gained in lives saved or in added quality adjusted life years. To be of value, a new technology for cervical cytology must be more effective in preventing cervical carcinoma. Dysplasia is considered a precursor of carcinoma, and detection of dysplasia has been a surrogate for prevention of cervical carcinoma, but dysplasia does not always lead to carcinoma, least of all mild dysplasia, and policy makers ultimately will insist that a favorable change in health outcome be effected by new technology before it is allocated resources. Alternatively, new technologies may lower cost, perhaps by modifying screening or rescreening procedures according to known risk; by improved cytopreparatory techniques that simplify, improve or speed screening; or by monitoring devices that minimize screening error. In each case the performance attributes of the instrument or human instrument process should be evaluated in the intended use environment. ONGOING ISSUES: While current cervical cytology methodology is one of the most effective means of cancer prevention, there continues to be development of new techniques to increase the sensitivity and specificity of this test. With present fiscal constraints, these will be subject to stringent cost/benefit analyses in which the medical profession must play a key role. Such analyses can be quite complicated, considering the additional costs or cost savings of clinical follow-up procedures and the reliability of dysplasias detected by cytology as a surrogate for cervical carcinoma in calculating quality of life years saved.

Attitude of Health Personnel↗
PubMedDate not supplied

Cost-effectiveness of rescreening conventionally prepared cervical smears by PAPNET testing.

OBJECTIVE: This study explored the cost-effectiveness of the use of PAPNET testing-supplemental, neural network-based testing used to increase the accuracy of cervical smear screening practice. STUDY DESIGN: Using a model adapted from one developed under contract from the United States Congress Office of Technology Assessment to evaluate cost-effectiveness of cervical cancer screening in elderly women, the study evaluated U.S. women aged 20-64. The study reviewed various screening intervals and examined the course of follow-up (i.e., repeat abnormal smear vs. immediate colposcopy) to offer a range into which most routine medical practice will fall. RESULTS: Assuming a false negative rate of 25% for low grade squamous intraepithelial lesion (SIL) and 15% for high grade SIL and applying increased sensitivity of 30% from PAPNET, we can expect a cost of $48,474 per life-year saved among biennially screened women. For women screened triennially, as recommended by most groups, the cost per life-year saved is $25,185. CONCLUSION: The PAPNET rescreening program is an economical approach to decreasing mortality and morbidity from cervical cancer and compares favorably to other commonly used interventions and diagnostic procedures.

Adult↗
PubMedDate not supplied

Bayesian analysis of diastolic blood pressure measurement.

A mathematical model is presented for measurements that include substantial fluctuation and error. Under the assumptions that the fluctuation-error variance is the same for all subjects, and that the distributions of fluctuation-error variance within subjects and "true" values of the measurements in the population are normal, Bayes' theorem produces a simple estimate of the "true" value of a measurement, and a standard error, conditional on a single observation. The model is easily extended to several observations. Methods for estimating the parameters of the model from a data set are presented, and applied to diastolic blood pressures of patients in the authors' primary care clinic. The test-retest reliability of a single blood pressure measurement for this population is 0.41. Because continuous measurements are often dichotomized into "normal" and "abnormal" ranges by a threshold criterion, the authors present formulas for the positive predictive value when a decision rule based on a given number of observations is used in a population with respect to a threshold criterion for the "true" values. For example, classifying their patients as hypertensive on the basis of the average of two readings exceeding 90 mm Hg diastolic pressure would have a positive predictive value of 52% for the "gold standard" of average diastolic pressure exceeding 90 mm Hg. Formulas to calculate the frequency with which patients will be classified "abnormal" by one decision rule but will be classified "normal" by later application of another rule are provided and used to "predict" the frequency with which this crossover phenomenon should have occurred in the enrollment phase of the Hypertension Detection and Follow-up Programs.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMedDate not supplied

Sequential analysis in a Bayesian model of diastolic blood pressure measurement.

A sequential method for diagnosing or excluding hypertension based on the Bayesian model of diastolic blood pressure presented in a companion article is presented. The likelihood ratio method of Wald is modified to include the effects of a prior probability distribution and to constrain the strategy to achieve specified positive and negative predictive values. The resulting formulas for upper and lower limits to diagnose and exclude diastolic hypertension can be evaluated using a hand calculator and a table of areas of the standard normal distribution. The strategy is illustrated for a population having a blood pressure distribution similar to that of the cohort screened for participation in the Hypertension Detection and Follow-up Program, with 90 mm Hg as the cutoff defining hypertension and required positive and negative predictive values of 95%. The performance of the strategy was simulated using Monte Carlo methods. The median number of readings required for diagnosis is three, and 80% of subjects are diagnosed in 11 or fewer readings. In contrast to the strategy's 95% predictive values, a fixed-number-of-measurements strategy requiring the same mean number of measurements has a positive predictive value of only 83% and a negative predictive value of 96%. When the parameters of the model have been properly measured or estimated, this method is practical, efficient, and accurate for diagnosing hypertension in a known population.

Bayes Theorem↗
PubMedDate not supplied

Sequential decision making with continuous disease states and measurements: I. Theory.

The question of whether to perform a continuous valued test to assess a continuous valued health state such as blood pressure or serum cholesterol is explored by decision analysis. Principal assumptions are that the underlying health state and measurement variability are both normally distributed, and that the impact of treatment on the utility of outcomes varies linearly with the underlying health state. Using Bayes' theorem, an expression for the expected utility of performing the test is derived and compared with immediate treatment or decision to withhold treatment. The calculations can be carried out with a pocket calculator and a table of the normal distribution. Iterating the analysis, a sequential decision making process is developed, leading to a series of no treat/test again and test again/treat thresholds with which a running average of independently obtained measurements can be compared to produce stepwise optimal results. The thresholds are readily calculated on a microcomputer. Finally, the conjugate-normal-linear model is extended to encompass the correlated observations that may be made on a single visit. This paper concentrates on the mathematics of decision making with continuous variables. The companion paper illustrates its application to diastolic blood pressure.

Bayes Theorem↗
PubMedDate not supplied

Sequential decision making with continuous disease states and measurements: II. Application to diastolic blood pressure.

The model and strategy for sequential decision making using normally distributed measurements proposed in a companion paper are applied to the problem of diagnosing diastolic hypertension. The assumptions of the model are discussed and justified clinically. Methods for assigning values to the model's parameters are explained and illustrated in the context of a hypothetical "generic" patient. Although current national recommendations and the sequential strategy both lead to an average of 1.89 measurements per patient prior to diagnosis, the sequential strategy applies a sequence of four or more measurements to 12% of patients. Fewer than 1% of patients would require ten or more measurements under this strategy. The sequential strategy leads to fewer patients' receiving unnecessary treatment and substantially higher expected utility for the patient. The role of multiple blood pressure determinations per visit is explored in the absence of appropriate estimates. Even under "best-case" assumptions, however, it is shown that obtaining more than one observation per visit is called for only in about 15% of visits. While the exact role of multiple determinations cannot be specified from existing data, it is likely to be much more limited than current recommendations suggest.

Computer Simulation↗
PubMedDate not supplied

Tuberculin screening: cost-effectiveness analysis of various testing schedules.

Because there is no tuberculin screening schedule currently recommended for adults, we used a Markov process in a cost-effectiveness analysis to determine an optimal strategy. We simulated the prognosis of a cohort of black 20-year-olds to evaluate the effects of various screening schedules with intradermal tuberculin and administration of isoniazid prophylaxis to those with positive results. The schedule with the lowest cost-effectiveness ratio is a single screening at 50 years of age, which costs $41,672 per quality-adjusted life year (QALY) gained. The cost-effectiveness ratio is nearly the same for all schedules involving a single screening between 30 and 70 years of age. Repeated screening strategies are less cost effective. Sensitivity analysis shows that the range of acceptable screening strategies changes significantly under alternate assumptions about the mortality from isoniazid hepatitis. However, screening at 50 years of age remains nearly optimal under the alternatives considered. Altering the values of other parameters generally produced only small changes. Tuberculin screening at 50 years of age should be added to primary care preventive practices because the strategy is as cost effective as standard health interventions and is robust to alternative assumptions. If further research confirms the base case assumptions about isoniazid toxicity, consideration should be given to increasing screening to every 10 years, which would produce a larger health benefit, albeit at substantially higher cost.

Adult↗
PubMedDate not supplied

Tuberculosis prevention: cost-effectiveness analysis of isoniazid chemoprophylaxis.

Isoniazid chemoprophylaxis is not recommended for all persons infected with tubercle bacilli. Because of the small but significant risk of isoniazid hepatotoxicity, chemoprophylaxis is reserved for only those at the highest risk of tuberculosis activation. To evaluate this policy, we performed a cost-effectiveness analysis of isoniazid chemoprophylaxis for two populations with positive tuberculin skin tests: recent tuberculin converters, who are at high risk for activation, and older tuberculin reactors, who have a low risk for activation and for whom chemoprophylaxis is not now recommended. The cost-effectiveness ratios found were stable, despite wide variations in model assumptions and probability estimates. For high-risk tuberculin reactors, chemoprophylaxis resulted in net medical care monetary savings, extended life expectancy, and fewer fatal illnesses. For low-risk tuberculin reactors, chemoprophylaxis resulted in positive, but small, health effects. Because the cost to gain these positive effects were also small, the resulting cost-effectiveness ratios were reasonable and in the realm of accepted prevention strategies: $12,625 to gain one year of life and $35,011 to avert one death. These findings suggest that the current policy is too restrictive and that many in the large population of low-risk tuberculin reactors should be considered for isoniazid chemoprophylaxis.

Adult↗