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Biomedical subjects

N Heddle

Publications and source records attributed to N Heddle.

11 recordsLinked to original sources
PubMed1996

Splenectomy done during hematologic remission to prevent relapse in patients with thrombotic thrombocytopenic purpura.

OBJECTIVE: To assess whether splenectomy done during hematologic remission reduces the relapse rate in patients with relapsing thrombotic thrombocytopenic purpura. DESIGN: Consecutive case series. SETTING: Tertiary care teaching hospital. PATIENTS: 6 consecutive patients seen during a 10-year period who had had one or more relapses of thrombotic thrombocytopenic purpura. INTERVENTIONS: All patients had elective splenectomy while in hematologic remission and were followed after surgery for as long as 8.0 years. MEASUREMENTS: Attack rates (events per year) were calculated for each patient from time of presentation to time of splenectomy and from time of splenectomy to January 1996. RESULTS: A total of 26 episodes of thrombotic thrombocytopenic purpura occurred over 22.3 patient-years before splenectomy. After splenectomy, 3 acute episodes occurred over 22.7 patient-years. The attack rate (+/-1 SD) decreased from 2.3 +/- 2.0 events per year to 0.1 +/- 0.1 events per year. CONCLUSION: In patients who have had one or more relapses of thrombotic thrombocytopenic purpura, splenectomy done during hematologic remission reduces the frequency of acute relapse and the resulting need for medical therapy.

Humans↗
PubMed1995

Basic statistics for clinicians: 4. Correlation and regression.

Correlation and regression help us to understand the relation between variables and to predict patients' status in regard to a particular variable of interest. Correlation examines the strength of the relation between two variables, neither of which is considered the variable one is trying to predict (the target variable). Regression analysis examines the ability of one or more factors, called independent variables, to predict a patient's status in regard to the target or dependent variable. Independent and dependent variables may be continuous (taking a wide range of values) or binary (dichotomous, yielding yes-or-no results). Regression models can be used to construct clinical prediction rules that help to guide clinical decisions. In considering regression and correlation, clinicians should pay more attention to the magnitude of the correlation or the predictive power of the regression than to whether the relation is statistically significant.

Data Interpretation, Statistical↗
PubMed1995

Basic statistics for clinicians: 3. Assessing the effects of treatment: measures of association.

In the third of a series of four articles the authors show the calculation of measures of association and discuss their usefulness in clinical decision making. From the rates of death or other "events" in experimental and control groups in a clinical trial, we can calculate the relative risk (RR) of the event after the experimental treatment, expressed as a percentage of the risk without such treatment. The absolute risk reduction (ARR) is the difference in the risk of an event between the groups. The relative risk reduction is the percentage of the baseline risk (the risk of an event in the control patients) removed as a result of therapy. The odds ratio (OR), which is the measure of choice in case-control studies, gives the ratio of the odds of an event in the experimental group to those in the control group. The OR and the RR provide limited information in reporting the results of prospective trials because they do not reflect changes in the baseline risk. The ARR and the number needed to treat, which tells the clinician how many patients need to be treated to prevent one event, reflect both the baseline risk and the relative risk reduction. If the timing of events is important--to determine whether treatment extends life, for example--survival curves are used to show when events occur over time.

Case-Control Studies↗
PubMed1995

Basic statistics for clinicians: 2. Interpreting study results: confidence intervals.

In the second of four articles, the authors discuss the "estimation" approach to interpreting study results. Whereas, in hypothesis testing, study results lead the reader to reject or accept a null hypothesis, in estimation the reader can assess whether a result is strong or weak, definitive or not. A confidence interval, based on the observed result and the size of the sample, is calculated. It provides a range of probabilities within which the true probability would lie 95% or 90% of the time, depending on the precision desired. It also provides a way of determining whether the sample is large enough to make the trial definitive. If the lower boundary of a confidence interval is above the threshold considered clinically significant, then the trial is positive and definitive, if the lower boundary is somewhat below the threshold, the trial is positive, but studies with larger samples are needed. Similarly, if the upper boundary of a confidence interval is below the threshold considered significant, the trial is negative and definitive. However, a negative result with a confidence interval that crosses the threshold means that trials with larger samples are needed to make a definitive determination of clinical importance.

Clinical Trials as Topic↗
PubMed1995

Basic statistics for clinicians: 1. Hypothesis testing.

In the first of a series of four articles the authors explain the statistical concepts of hypothesis testing and p values. In many clinical trials investigators test a null hypothesis that there is no difference between a new treatment and a placebo or between two treatments. The result of a single experiment will almost always show some difference between the experimental and the control groups. Is the difference due to chance, or is it large enough to reject the null hypothesis and conclude that there is a true difference in treatment effects? Statistical tests yield a p value: the probability that the experiment would show a difference as great or greater than that observed if the null hypothesis were true. By convention, p values of less than 0.05 are considered statistically significant, and investigators conclude that there is a real difference. However, the smaller the sample size, the greater the chance of erroneously concluding that the experimental treatment does not differ from the control--in statistical terms, the power of the test may be inadequate. Tests of several outcomes from one set of data may lead to an erroneous conclusion that an outcome is significant if the joint probability of the outcomes is not taken into account. Hypothesis testing has limitations, which will be discussed in the next article in the series.

Clinical Trials as Topic↗
PubMed1995

Noninfectious adverse effects of blood transfusion in the neonate.

There are many potential noninfectious complications that may be associated with the transfusion of blood products to the neonate. Most of these can be avoided by the careful preparation of the product according to current standards and the careful monitoring of the infant for metabolic changes during a transfusion. In general, there have been fewer systematic studies of transfusion-associated complications in neonates than in adults, possibly because of the difficulty of establishing a cause-effect relationship in the neonatal patient population. Such data, if available, would be useful for providing more effective blood product therapy to the neonate.

Animals↗
PubMed1993

An index of scientific quality for health reports in the lay press.

Although the quality of health reporting has been criticized for being unscientific, evaluations of health care reporting have been limited by the lack of a reliable and credible measure of scientific quality. We developed an index of scientific quality (ISQ) for health-related news reports and tested its reliability and sensibility. Items were generated from a survey of the literature and experts in research methodology. Items that were unclear, confusing or discriminated poorly between articles of high and low scientific quality were revised or deleted in an iterative process wherein potential criteria were independently applied to samples of 5 to 15 articles by 6 raters. To test the reliability of the final criteria 60 articles were drawn from three sampling frames: newspapers, magazines, and professional journals. Articles were intentionally selected to obtain a wide range of quality and topics. Two categories of raters were used: research assistants and physicians with research training. All 6 raters assessed all 60 articles. The sensibility of the index was tested by a questionnaire with 13 items related to face validity and content validity as well as other aspects of sensibility. The questionnaire was completed by 20 researchers and 13 health and science writers. The final ISQ includes 7 items that address the extent to which a report allows readers to draw conclusions about the applicability, validity and practical importance of the information that is reported. Chance corrected agreement (kappa) among all 6 raters for overall scientific quality was 0.62 (SE 0.02). The index was found to be sensible with only one major problem, the need for judgment in making ratings. While some degree of subjectivity appears to be inevitable in rating the scientific quality of health reports, the ISQ is acceptable reliable and credible and should be useful for evaluating and improving the scientific quality of health reporting.

Evaluation Studies as Topic↗
PubMed1981

HLA-restricted responses to M and N determinants in the primed lymphocyte test.

We have studied the role of MNSs determinants in the primed lymphocyte test (PLT). The data demonstrate that incompatibility associated with the M or N antigens causes HLA-restricted proliferative responses in PLT. Responses to the M or N determinants required the presence of the same HLA-A antigen(s) on both the stimulator and the responder cells. No effects of S or s incompatibility were observed in this test. This is the first report of lymphocyte proliferative responses to "minor" alloantigens that require corecognition of the MHC determinants. These observations suggest possible new biological functions of these blood group antigens.

Cytotoxicity Tests, Immunologic↗
PubMed1981

Transient Donath-Landsteiner haemolytic anaemia.

Five children with 'paroxysmal cold haemoglobinuria' are described. In all of them an upper respiratory tract infection preceded the episode of acute intravascular haemolysis and potentially pathogenic organisms were recovered from four. The haematological features are presented and the importance of technique in the detection of the pathognomonic antibody is stressed and discussed in detail. Although the clinical manifestations are usually self-limiting and of short duration, it may be necessary, because of the rapidity and severity of anaemia, to provide interim support with appropriate blood transfusion. Since the disease is not usually recurrent and not clearly related to exposure to cold, it is suggested that it be re-named Donath-Landsteiner haemolytic anaemia.

Antibodies↗
PubMedDate not supplied

Anti-Lu17.

Explore the source record for details and available documents.

Autoantibodies↗