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J R Beck

Publications and source records attributed to J R Beck.

At least 91 records · Page 5Linked to original sources
PubMed1988

Evaluating diagnostic performance of clinical tests by spreadsheet modeling. Bayesian analysis using Ri/Cj ratio as a unifying concept.

We present a general spreadsheet model for evaluating diagnostic performance of clinical tests. Our model depicts test results as an r X c matrix, with r possible test results and c possible clinical states. Analysis of this matrix is based on the Ri/Cj ratio, calculated as a number of subjects having a specified result Ri within a given clinical state Cj, divided by total subjects within this clinical state. From this model, we can identify three special cases: (1) a 2 X c matrix, with two possible test results of T+ or T-, over c possible clinical states; (2) an r X 2 matrix, with r possible test results, over two possible clinical states of D+ or D-; and (3) a 2 X 2 matrix, with two possible test results over two possible clinical states. Application of the Ri/Cj ratio to the r X c matrix provides a useful approach to graphic analysis of multiple test results over multiple clinical states. The Ri/Cj ratio also provides a general approach to Bayesian analysis, in which likelihood ratio, relative operating characteristic analysis, sensitivity, and specificity represent special cases or special applications.

Bayes Theorem↗
PubMed1987

Early invasive cancer in adenomatous colonic polyps ("malignant polyps"). Evaluation of the therapeutic options by decision analysis.

The management alternatives of segmental colonic resection versus follow-up alone for colonic adenomas containing early invasive carcinoma (i.e., polypectomy resection margin free of tumor) were evaluated by decision tree analysis. Using data from the literature, the major variables influencing the decision were as follows: probability of residual disease after polypectomy, operative efficacy (defined as the chance of curing a tumor that would otherwise recur without surgery), and operative mortality. For a hypothetical patient with low operative risk (operative mortality of 0.2%), resection would yield the best outcome in terms of life expectancy as long as the probability of residual disease was greater than 0.5%. Extensive analysis of the impact of changes in assumptions about the parameters characterizing the problem showed this conclusion to be unchanging over wide ranges of operative efficacy and probability of residual disease. However, the decision to do a secondary resection in this situation was still close because surgery was only marginally justifiable on economic grounds. Observation would be preferred in patients with higher operative risk (operative mortality greater than 2%).

Adenocarcinoma↗
PubMed1987

A computer-based Markov decision analysis of the management of symptomatic bifascicular block: the threshold probability for pacing.

This review illustrates the use of computer-based Markov models to estimate cost-effectiveness and prognosis in a complex problem in clinical cardiology. Decision analysis and cost-effectiveness analysis were used to assess whether to implant a permanent cardiac pacemaker, treat with drugs, perform electrophysiologic studies or observe patients who have two clinical features--syncope and bifascicular block--that may or may not be causally related. Using a Markov process model, a computer program simulated the prognosis of five cohorts of such patients--one treated conservatively, one given empiric antiarrhythmic drug therapy, one receiving a pacemaker, one treated with empiric drugs and pacing and one tested with electrophysiologic studies. On the basis of data from published reports and expert opinion, quality-adjusted life expectancy was calculated by summing the average time a member of each cohort would survive with and without symptoms for each initial treatment choice. The costs were estimated from 1985 hospital charges. For patients with normal left ventricular function, electrophysiologic testing provides a benefit of 14 quality-adjusted months of life over observation, at an additional cost of $24,200. Empiric pacing would add 2.5 additional months, at a further cost of $14,300. In patients with poor left ventricular function, empiric drug therapy offers 1.5 additional quality-adjusted months over observation, at a cost of $6,900. Electrophysiologic testing provides a further 16.5 months at an additional cost of $16,900. These results hold when the relation between symptoms and arrhythmia is not firmly established. Varying the probabilities of underlying ventricular tachyarrhythmias, bradyarrhythmic conduction defects or noncardiac causes of syncope affects the cost-effectiveness relative to the alternative treatments.

Anti-Arrhythmia Agents↗
PubMed1987

Biochemical profiles. Applications in ambulatory screening and preadmission testing of adults.

Evidence bearing on the utility of biochemical profiles for ambulatory care screening and preadmission testing was reviewed, and recommendations were formulated. Certain biostatistical principles relevant to this analysis include the concepts of regression to the mean, the meaning of biochemical "normality" (particularly as it relates to multiple testing), and the effects of disease prevalence on the post-test probability of disease for individual test results. Applying these principles to a typical 12-test battery in asymptomatic adults, one would expect a low yield of unanticipated diagnoses and a high proportion of false-positive results. For the typical test battery, the empirical evidence supports these expectations in ambulatory care screening. In addition, routine preadmission use of biochemical profiles is not supported by studies examining their impact on patient care, hospital costs, or lengths of stay. Whereas components of these profiles can be endorsed for screening or preadmission testing, we recommend that the routine use of the entire profile be abandoned in these settings.

Adult↗
PubMed1986

Autologous bone marrow transplantation in acute myelogenous leukemia: in vitro treatment with myeloid cell-specific monoclonal antibodies.

Second or third chemotherapy-induced remissions in acute myelogenous leukemia (AML) are limited by early relapse of the leukemia. We developed monoclonal antibodies (MoAbs) that are cytotoxic to myeloid leukemia cells to treat bone marrow from these patients ex vivo for autologous transplantation. In this pilot study, bone marrow was harvested from ten patients with AML in remission, treated with one or two complement-fixing MoAbs, PM-81 and AML-2-23, which react with myeloid differentiation antigens, incubated with rabbit complement, and cryopreserved. These MoAbs were chosen because they have broad reactivity with AML cells but not with pluripotent progenitor cells. At the time of transplant, 6 patients were in second complete remission, 1 each was in third complete or partial remission, and 2 were in early first relapse. The patients were treated with cyclophosphamide (60 mg/kg a day for 2 days) and total body irradiation (200 cGy twice a day for 3 days) and given infusions of MoAb-treated bone marrow. Full bone marrow reconstitution was observed in eight patients; two patients did not recover platelets. Seven of the ten patients are surviving and disease-free at 21.0, 15.0, 13.0, 10.0, 6.0, 3.0, and 2.0 months posttransplant. Treating bone marrow with MoAbs to myeloid differentiation antigens does not interfere with pluripotential stem cell engraftment. Longer follow-up and a controlled study are necessary to prove that the apparent efficacy of this therapeutic approach in some patients is attributable to MoAb-mediated killing of leukemia cells.

Antibodies, Monoclonal↗
PubMed1986

Postoperative elevation of human peripheral blood monocyte tissue factor coagulant activity.

The generation of tissue factor coagulant activity was measured in short-term cultures of mixed mononuclear cells prepared from peripheral blood. Levels of tissue factor activity were significantly increased (P less than 0.05) at 3 and 7 days after surgery in patients who had had uncomplicated surgical procedures when comparison was made with preoperative levels and with levels observed at the same time intervals in patients who had had a general anesthetic without surgery. Activity in patients who had had surgery returned to preoperative levels at 14 days after surgery. Findings were similar whether or not phytohemagglutinin was added to the cultures to enhance tissue factor generation and whether or not tissue factor activity was quantified on the basis of activity per culture or per monocyte. No change in monocyte counts occurred in the interval during which these studies were performed. Because the increase in monocyte tissue factor activity coincided with the interval after surgery when patients are known to be at greatest risk of thromboembolism, we postulate that the capacity of monocytes to generate increased tissue factor activity may contribute to postoperative hypercoagulability.

Blood Coagulation↗
PubMed1986

Laboratory decision science applied to chemometrics: strategic testing of thyroid function.

Clinical decision analysis and cost-effectiveness analysis have begun to penetrate academic laboratory medicine. Decision science offers tools by which clinical chemical tests may be evaluated for their medical efficacy and economic feasibility. In the "treat, test, observe" paradigm it provides a framework for placing new laboratory tests in an appropriate clinical context. A general overview of the decision analysis method and the laboratory-oriented model is presented, with an application to the development of strategies for hospital-based testing of thyroid function.

Costs and Cost Analysis↗
PubMed1986

The use of relative operating characteristic (ROC) curves in test performance evaluation.

Relative (or receiver) operating characteristic (ROC) curves are a graphical representation of the relationship between sensitivity and specificity of a laboratory test over all possible diagnostic cutoff values. Laboratory medicine has been slow to adopt the use of ROC curves for the analysis of diagnostic test performance. In this tutorial, we discuss the advantages and limitations of the ROC curve for clinical decision making in laboratory medicine. We demonstrate the construction and statistical uses of ROC analysis, review its published applications in clinical pathology, and comment on its role in the decision analytic framework in laboratory medicine.

Clinical Laboratory Techniques↗
PubMed1986

Efficacy of silver sulfadiazine in the treatment of prosthetic arterial bypass graft infection.

Infection is an uncommon but unfortunate complication of prosthetic arterial bypass grafting. Because previously described methods of treatment of such infections which do not involve excision of the graft have not met with uniform success, we undertook a study of the efficacy of silver sulfadiazine cream in the treatment of Staphylococcus aureus infections of polytetrafluoroethylene carotid artery bypass grafts in dogs. At the time of bilateral grafts placement in 14 dogs, wounds were inoculated with at least 2 X 10(7) organisms. Three days later all wounds were opened. The wounds of seven dogs were treated with daily applications of silver sulfadiazine cream and the wounds of the other dogs were treated with daily applications of povidone iodine ointment. The dogs were sacrificed at 30 days or at the earliest evidence of arterial beeding from the wounds, whichever came first. Cultures of the wound were taken, and graft and artery histologic findings were studied at the time of sacrifice. Although survival of the dogs treated with silver sulfadiazine was marginally better than that of the dogs treated with povidone iodine, viable bacteria were present in microabscesses in many apparently healed wounds in the former group. We conclude that daily applications of silver sulfadiazine cream does not reliably eradicate staphylococcal infections involving polytetrafluoroethylene arterial bypass grafts.

Abscess↗
PubMed1984

The cold thyroid nodule: an analysis of diagnostic and therapeutic options.

We applied decision analysis to the controversy over the management of the solitary nonfunctioning thyroid nodule. Three standard management plans were considered: immediate subtotal thyroidectomy; a six month trial of thyroid suppression with L-thyroxine, with non-suppressible lesions being removed surgically; and aspiration cytology followed by surgery or thyroid suppression based on the cytologic examination. The literature formed the basis for quantitative assumptions of the analysis, including the consequences of thyroidectomy, the probability of malignancy, the types and prognoses of cancers found at operation, the likelihood of successful suppression adn relapse, and the possible results of aspiration cytology. We used Bayes' rule to revise the probability of cancer on the basis of cytological results. The relative worths of the 59 possible diagnostic and therapeutic outcomes were expressed as quality-adjusted life expectancies. The expected utility of each management plan was determined by "folding back" the decision tree. Although we found that each possible approach yielded a quality-adjusted life expectancy very close to that of the healthy population, aspiration biopsy with cytologic examination appeared slightly superior. Extensive sensitivity analyses demonstrated that either aspiration biopsy or immediate thyroid suppression was the treatment of choice over a wide range of assumptions, although in no case did the benefit exceed 1 year of life. We conclude that all therapies for cold thyroid nodule are essentially equal, viewed in terms of mortality and morbidity. The decision to operate, suppress or aspirate is thus a " tossup ", dependent in the individual case upon such subjective factors as psychological disutility , relative cost, and attitudes toward operative risk and long-term medical therapy. The controversy concerning the "best" management of the cold thyroid nodule is an illusion: quantitative analysis shows the futility of pursuing the debate any further.

Antithyroid Agents↗
PubMed1984

The effects of sample size on reticulocyte counting and stool examination. The binomial and poisson distributions in laboratory medicine.

In tests that involve counting or searching for discrete objects, clinical laboratory specimens that are too small produce insensitive and imprecise test results. We found that ten of 57 surveyed New England hospital laboratories examine less than a 50-mg stool sample for parasite eggs; they are, therefore, unlikely to detect infections characterized by low concentrations of eggs in stool. Conversely, all 57 laboratories use the traditional, appropriate sample size of at least 1,000 RBCs for reticulocyte counting. In this report, we discuss theoretical and practical considerations in small sample testing.

Blood Cell Count↗
PubMed1983

Monocyte tissue factor activity in anticoagulant-treated patients.

The tissue factor coagulant activity of peripheral blood monocytes was measured in 20 patients on long-term anticoagulant treatment with warfarin and in 21 healthy individuals. Contrary to expectations, tissue factor activity was not reduced in the warfarin-treated group and was, in fact, elevated in several patients. No relationship existed between the daily warfarin dose or the degree of prolongation of the prothrombin time and the monocyte tissue factor activity. These results indicate that monocyte tissue factor activity is not necessarily reduced to below normal levels with warfarin treatment.

Cardiovascular Diseases↗