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PubMed1994

Sensitivities and predictive values of paraclinical tests for diagnosing multiple sclerosis.

The sensitivities and predictive values of visual, somatosensory, and brain auditory evoked potentials (EPs), cerebrospinal fluid oligoclonal banding (CSF-OB) and magnetic resonance imaging (MRI) were evaluated for the early diagnosis of clinically definite multiple sclerosis (CDMS). Paraclinical evidence of asymptomatic lesions allows a diagnosis of CDMS. Eighty-two patients in whom MS was suspected but diagnosis of CDMS was not possible entered the study prospectively. Paraclinical examinations were performed at entry. Patients were examined and underwent EPs every 6 months, and MRI yearly. After a mean follow-up of 2.9 years, 28 patients (34%) had developed CDMS (McDonald-Halliday criteria). The initial MRI was strongly suggestive of MS in 19 of these (68%), while 27 (96%) had at least one MS-like abnormality in the initial MRI. CSF-OB and EPs had lower sensitivities. CDMS developed during follow-up in 19 of the 36 patients (53%) who had an initial MRI strongly suggestive of MS but in only 1 of the 25 who had normal MRI when first studied. These results support previous conclusions that MRI is the most sensitive test for detecting white matter asymptomatic lesions, and the most predictive for the diagnosis of CDMS.

Adolescent↗
PubMed1990

Predictive value of susceptibility tests for the outcome of antibacterial therapy.

A total of 510 charts of patients who received antibacterial agents were examined for clinical outcome and microbiology findings. A total of 382 patients (75%) had one or more specimens submitted for culture and susceptibility tests before the administration of the drugs; 298 (78%) of these had positive cultures and susceptibility tests were done. A total of 18 species were isolated. Of the 298 patients with organisms of known susceptibilities, 271 (91%) received antibacterial agents to which the respective organisms were susceptible and 219 of these patients (81%) improved (P less than 0.05). This high rate of good infectious diseases practice is probably due to two factors: (1) susceptibility tests results were available in most cases the next day after the submission of a specimen; (2) the medical board distributed guidelines for the use of antibiotics and monitored the compliance closely. The patients treated with antibacterial agents to which the bacteria were resistant improved in 3% and did not improve in 82% (P less than 0.05) of the patients. This study shows that choosing an antibacterial agent in accordance to the susceptibility test resulted in a high rate of improvement. When the choice of agent disregarded bacterial resistance in vitro, therapy almost always ended in failure. Therefore, susceptibility tests in vitro have a good predictive value for the outcome of antibacterial therapy.

Anti-Bacterial Agents↗
PubMed1998

Predictive value of an adherence test for acute otitis media.

The predictive value of an in vitro adherence test of the bacterium Streptococcus pneumoniae for the development of recurrent otitis media was calculated 5 years after the initial test. Nasopharyngeal cells from 56 children suffering from acute otitis media (AOM) and from healthy children were tested for adherence of a standard pneumococcal type (capsular serotype 6). The average adherence of the bacteria to epithelial cells from the group suffering from AOM was greater than the average adherence in the control group (p < 0.005), both when adherence was counted microscopically and radioactively. Subjects were followed up periodically over a 5-year period. Four out of 5 healthy children who had high mean adherence values experienced AOM during the 5 years, and 1 child classified as AOM-prone was found to be healthy. Based on the retrospective data, the positive predictive value of this test was 98.2%, and the negative predictive value was 90.7%.

Acute Disease↗
PubMed1985

The prospective diagnostic value of real-time cholecystosonography.

A series of 82 consecutive patients scheduled for operation, with pre-operatively obtained P.O. cholecystography and in some cases also I.V. cholangiography, is presented. All patients had cholecystosonography performed "blindly" the day prior to the operation (76 had a cholecystectomy and six had a vagotomy). Based upon the operative findings, the diagnostic value of ultrasonic examination for gallstones can be calculated to predictive value of positive test--1.00; predictive value of negative test--0.71. The diagnostic failures are discussed but it is not possible to predict which patients will benefit more from peroral cholecystography rather than from ultrasound. It is concluded that cholecystosonography is a safe alternative to peroral cholecystography.

Cholangiography↗
PubMed1979

The magnitude of exercise-induced ST segment depression and the predictive value of exercise testing.

The assess whether the magnitude of exercise induced ST segment depression improves the predictive values of symptom limited exercise tests, and helps in the recognition of patients with more severe coronary heart disease, 90 consecutive patients with positive treadmill tests who also underwent selective coronary arteriography were reviewed. The predictive value improved progressively with the increasing ST depression and was most reliable in a select group of patients with normal electrocardiographic baseline who were not receiving digitalis (73% with ST depression greater than or equal to 1 mm to 100% with ST depression greater than or equal to 4 mm). The incidence of 2 and 3 vessel disease increased from 61% with ST depression greater than or equal to 1 mm in the overall population to 100% with ST depression greater than or equal to 4 mm in the select group, and the incidence of left main trunk lesions increased, respectively from 6 to 30%. The prediction of 2 and 3 vessels disease was found to be significantly greater when patients were dichotomized into those with ST depression greater than or equal to 4 mm compared to less than 4 mm. It is concluded that the magnitude of ST segment depression definitely improves the predictive values of exercise tests as well as the ability to recognize the patients with more severe disease. However, the markedly positive exercise tests cannot be utilized to accurately predict the presence of 2 or 3 vessel disease in individual cases unless ST depression attains 4 mm or more in patients with normal electrocardiographic baseline who are not taking digitalis. In this group, the ability to predict left main trunk lesion is approximately 30%.

Coronary Angiography↗
PubMed2005

The efficacy assessment of thigh volume in predicting intrauterine fetal growth restriction by three-dimensional ultrasound.

Intrauterine growth restriction (IUGR) is an important issue in perinatology. To assess the efficacy of fetal thigh volume (ThVol) in predicting IUGR, we undertook a prospective cross-sectional study using quantitative 3-D ultrasound (US). During the study period, 30 fetuses with IUGR and 282 fetuses with non-IUGR were included for the ThVol assessment in utero by 3-D US. All the fetuses were singletons and had follow-up to the delivery to determine whether they were complicated with IUGR or not. Our results showed fetal ThVol assessed by 3-D US can differentiate fetuses with IUGR from fetuses with non-IUGR well. Using the 10th percentile as the screening threshold, the sensitivity of fetal ThVol in predicting IUGR was 86.6%, with specificity 91.1%, predictive value of positive test 51.0%, predictive value of negative test 98.5% and accuracy 90.7%. In conclusion, fetal ThVol assessed by quantitative 3-D US can be used to predict fetuses with IUGR antenatally. We believe fetal ThVol assessment by 3-D US would be a useful test in detecting fetuses with IUGR.

Anthropometry↗
PubMed2006

Predicting fetal growth restriction with liver volume by three-dimensional ultrasound: efficacy evaluation.

It is well-documented that fetal growth restriction (FGR) may have increased risks of perinatal morbidity and mortality. Early detection of FGR is crucial in prenatal care and daily practice. We undertook a prospective and cross-sectional study using quantitative 3-D ultrasound (US) to assess the efficacy of fetal liver volume (LV) in predicting FGR. During the study period, 42 fetuses with FGR and 375 fetuses without FGR were included for the LV assessment in utero by 3-D US. All the fetuses were singletons and had follow-up to delivery to ensure whether they were complicated with FGR or not. Our results revealed that fetal LV assessed by 3-D US can differentiate well fetuses with FGR from those without FGR. The sensitivity of fetal LV in predicting FGR was 97.6%, with specificity 93.6%, predictive value of positive test 63%, predictive value of negative test 99.7% and accuracy 94%. In conclusion, fetal LV assessed by quantitative 3-D US can be used to predict fetuses with FGR antenatally. Our data support that fetal LV assessment by 3-D US would be a useful test in detecting fetuses with FGR.

Cross-Sectional Studies↗
PubMed1986

Predictive value of skin prick tests and radioallergosorbent tests for clinical allergy to dogs and cats.

The predictive value and post-test probability of disease were compared for skin prick tests and radioallergosorbent tests (RASTs) in 168 children suspected of clinical allergy to dogs and cats. The skin tests included negative and positive (histamine) controls. The results of RASTs with the same allergen extracts were expressed in relation to the results with allergen-specific pooled reference serum. All the tests were performed blind. The predictive values of positive test results were comparable and low (53% to 76%), whereas the predictive values of negative test results were comparable and high (88% to 95%). The post-test probability of clinical allergy to dog or cat allergen, based on the prevalence rates in the referral population (15.1% and 22.5% respectively), increased to between 46% and 67% for positive test results and decreased to between 4% and 8% for negative results, which suggests that the primary role of skin prick tests and RASTs is in eliminating the diagnosis of clinical allergy.

Adolescent↗
PubMed1993

Comparison of vidas Clostridium difficile toxin-A assay and premier C. difficile toxin-A assay to cytotoxin-B tissue culture assay for the detection of toxins of C. difficile.

Damage to the intestinal mucosa by Clostridium difficile (CD) is toxin mediated. Two enzyme immunoassays (EIAs) for toxin-A detection, the automated Vitek immunodiagnostic assay system CDA (Vidas CDA), and the Premier toxin A (Premier) were tested for their ability to detect toxin A in 301 stool samples and compared with an in-house tissue culture assay for toxin B (TCA). Of these 301 samples, 49 were TCA positive and 252 were TCA negative. Agreement between Vidas CDA and TCA on the initial run was 85% (255 of 301) and increased to 94% (278 of 296) when discordant samples were retested from available frozen specimens. Corresponding levels of agreement for Premier were 91% (272 of 301) and 98% (284 of 288), respectively. If tissue culture positivity at any titer was used as the sole criterion for positivity of the specimen, agreement with positive TCA before and after repeat testing was 57% (26 of 49) and 74% (34 of 46) for Vidas CDA and 65% (32 of 49) and 95% (36 of 38) for Premier. Agreement with negative TCA titers was good: 90% for Vidas CDA and 95% for Premier, and 98% for Vidas CDA and 99% for Premier after repeat testing. Predictive values positive and negative after repeat testing were, respectively, 88% and 96% for Vidas CDA, and 95% and 99% for Premier. Results for the automated and manual EIA methods for detection of C. difficile toxin A were obtained in 2.5 h as compared with 36-48 h for tissue culture.

Bacterial Proteins↗
PubMed2002

Ten-year risk of osteoporotic fracture and the effect of risk factors on screening strategies.

Bone mineral density (BMD) measurements are widely used to estimate the risk of osteoporotic fractures. In addition, many other risk factors have been identified, some of which are known to add to the risk independently of BMD measurements. The combination of BMD with such risk factors increases the gradient of risk/standard deviation (SD) than that achieved by BMD alone. In this paper, we report the fracture probabilities according to age, gender, and relative risk, and have investigated the effects of changes in the gradient of risk for osteoporotic fractures on the sensitivity and specificity of assessments, modeled on the population of Sweden. Ten-year risks of hip, clinical vertebral, forearm, or proximal humeral fracture were computed with increments in gradient of risk that varied from 1.5 to 6.0 per SD change in skeletal risk. The identification of high-risk groups had little effect on the specificity of assessments, but increased the sensitivity over a wide range of assumptions. The inclusion of all four fracture types had little effect on sensitivity, but increased the positive predictive value of the test. Positive predictive value also increased with age, so that values greater than 50% were obtained testing women at the age of 65 years with modest gradient of risk of 2.0-2.5/SD when small segments of the population were targeted (0.5-5%). Screening of women to direct intervention at the age of 65 years and targeting 25% of the population could save up to 23% of all fractures in women over the next 10 years by the use of multiple tests with a moderate gradient of risk (RR = 2.0/SD). Such gradients might be achieved with the use of multiple risk factors to identify patients at risk.

Age Factors↗
PubMed2002

Emerging ethical issues in pharmacogenomics: from research to clinical practice.

Pharmacogenomics holds much promise for the application of genetic information to the improvement of clinical care. Ethical issues for pharmacogenomics arise at the intersection of the spheres of drug development and genetic testing. Clinical drug trial designs which use subject selection based on genotype must consider the features of scientific validity, social value and risk-benefit ratio, and later, the impact of this strategy on post-market studies and clinical use of drugs. Although the testing context for pharmacogenomic tests is different from other genetic tests, decisions to use any new clinical tests in medical practice will require evaluation of not only the benefit linked to improved drug use but also the risks arising in part from the scale of testing, predictive value and collateral potential of the genetic test. Integration of pharmacogenomic information into clinical practice will require clinical trials to assess their clinical usefulness, including the impact of tests on therapeutic outcomes. Trials will also be needed to demonstrate the effectiveness of education, informed consent and counseling.

Animals↗
PubMed2003

Performance characteristics and quality control of community based ultrasound surveys for cystic and alveolar echinococcosis.

The probability of disease given the results of a test, is called the predictive value of the test. The predictive value of a test is not a property of the test itself but will vary according to the prevalence of the disease in the studied population. The positive predictive value (PPV) is the probability that the subject tested has the disease given that a positive result is obtained. The negative predictive value (NPV) is the probability that the subject tested is normal given that a negative result is obtained. As the prevalence of a disease in a population approaches zero so does the PPV and most of the positive cases will be 'false positives'. Conversely the NPV will be very high at low prevalences and there will be few 'false negative' results. The sensitivity and specificity of a test are properties of the test and do not vary with prevalence. The higher the sensitivity and specificity of a particular test the greater the predictive values will be at any given prevalence of the disease. Ultrasound (US) is increasingly used for detecting lesions due to cystic and alveolar echinococcosis (CE and AE) and portable US scanners facilitate community based mass screening surveys in remote rural communities. Screening is justified with AE and CE in endemic areas as diagnosis at an early stage can lead to a better prognosis following treatment. The sensitivity and specificity of US has been reported to be between 88-98% and 95-100% respectively for CE and the sensitivity is a little higher for AE. Both species have pathognomonic signs on US and the technique is considered to be the 'gold standard' although it is still an imperfect test. Clinical, laboratory and epidemiological data also play an important role in the diagnosis of CE and AE. US results where possible, should be evaluated in relation to these findings. Suspected CE and AE images, may benefit from the use of other imaging techniques such as magnetic resonance imaging, computerised tomography and in the case of AE angiography or cholangiography. Immunological tests or molecular biological techniques also provide a useful back up, especially for AE. As sensitivity and specificity are properties of the US diagnostic test they should not vary if the case mix reported in different studies remains the same. The use of the WHO standardised US classifications for CE and AE should be used so that the properties of the test are standardised. Quality control of field based studies will depend on geographical variations in the case mix and the relative proportions of cyst types without pathognomonic signs. The latter will have the most bearing on variations in specificity, as would the use of different classifications. Inter- and intra-observer variability and differences in prevalence will affect the performance of US in different endemic settings. Community based surveys must adhere to the highest ethical standards and the outcome of surveys should result in appropriate treatment and follow-up strategies for all infected individuals and suspected cases found during the surveys.

Animals↗
PubMed2006

Comparing the predictive values of diagnostic tests: sample size and analysis for paired study designs.

BACKGROUND: Although statistical methodology is well developed for comparing diagnostic tests in terms of their sensitivities and specificities, comparative inference about predictive values is not. PURPOSE: In this paper we consider the design and analysis of studies comparing the positive and negative predictive values of two diagnostic tests that are measured on all subjects. METHODS: We focus on comparing tests using the relative positive and negative predictive values. We discuss directly estimating these quantities from the data and derive analytic variance expressions. Sample size formulas for study design ensue. RESULTS: We analyze data on patients with cystic fibrosis to illustrate the methodology. This approach is compared and contrasted with an existing regression framework that can also be used for similar analysis purposes and yields similar results. CONCLUSIONS: We have developed a new approach for comparing the predictive values of two tests that gives rise to sample size formulas for study design.

Biometry↗
PubMed1986

Relative value of clinical variables, bicycle ergometry, rest radionuclide ventriculography and 24 hour ambulatory electrocardiographic monitoring at discharge to predict 1 year survival after myocardial infarction.

The relative value of predischarge clinical variables, bicycle ergometry, radionuclide ventriculography and 24 hour ambulatory electrocardiographic monitoring for predicting survival during the first year in 351 hospital survivors of acute myocardial infarction was assessed. Discriminant function analysis showed that in patients eligible for stress testing the extent of blood pressure increase during exercise slightly improved the predictive accuracy beyond that of simple clinical variables (history of previous myocardial infarction, persistent heart failure after the acute phase of infarction and use of digitalis at discharge), whereas radionuclide ventriculography and 24 hour electrocardiographic monitoring did not. The predictive value for mortality was 12% with clinical variables alone and 15% with the stress test added. Radionuclide ventriculography and 24 hour electrocardiographic monitoring were slightly additive to clinical information in the whole group of patients independent of the eligibility for stress testing (predictive value for mortality 24% with clinical variables alone and 26% with radionuclide ejection fraction and 24 hour electrocardiographic monitoring added). It is concluded that the appropriate use of simple clinical variables and stress testing is sufficient for risk stratification in postinfarction patients, whereas radionuclide ventriculography and 24 hour electrocardiographic monitoring should be limited to patients not eligible for stress testing.

Aged↗
PubMed2001

Posttransplant microbiological surveillance.

Posttransplant microbiological surveillance should be used when the likelihood of infection in a transplant recipient is high and the sensitivity and specificity of the test can provide a high positive or negative predictive value. Testing is also performed in some instances to monitor the patient's response to therapy. Examples of successful posttransplant microbiological surveillance include molecular detection of cytomegalovirus and Epstein-Barr virus and virus load determinations, as well as hepatitis B and C detection and virus load testing. Routine fungal and bacterial surveillance are generally not necessary, except for Candida colonization detection or vancomycin-resistant enterococcal detection in high-risk subgroups. The organ transplanted may also play a role in the type of routine surveillance recommended.

Humans↗
PubMed1990

Introduction to biostatistics: Part 3, Sensitivity, specificity, predictive value, and hypothesis testing.

Diagnostic tests guide physicians in assessment of clinical disease states, just as statistical tests guide scientists in the testing of scientific hypotheses. Sensitivity and specificity are properties of diagnostic tests and are not predictive of disease in individual patients. Positive and negative predictive values are predictive of disease in patients and are dependent on both the diagnostic test used and the prevalence of disease in the population studied. These concepts are best illustrated by study of a two by two table of possible outcomes of testing, which shows that diagnostic tests may lead to correct or erroneous clinical conclusions. In a similar manner, hypothesis testing may or may not yield correct conclusions. A two by two table of possible outcomes shows that two types of errors in hypothesis testing are possible. One can falsely conclude that a significant difference exists between groups (type I error). The probability of a type I error is alpha. One can falsely conclude that no difference exists between groups (type II error). The probability of a type II error is beta. The consequence and probability of these errors depend on the nature of the research study. Statistical power indicates the ability of a research study to detect a significant difference between populations, when a significant difference truly exists. Power equals 1-beta. Because hypothesis testing yields "yes" or "no" answers, confidence intervals can be calculated to complement the results of hypothesis testing. Finally, just as some abnormal laboratory values can be ignored clinically, some statistical differences may not be relevant clinically.

Biometry↗
PubMed2006

Improving the diagnosis of bipolar disorder: predictive value of screening tests.

OBJECTIVE: To examine the impact of assumptions about prevalence or prior clinical probability of bipolar disorder on the clinical performance (predictive values) of diagnostic screening tests. METHOD: Sensitivity and specificity data from four reports on two bipolar screening instruments (the Mood Disorders Questionnaire and the Bipolar Spectrum Diagnostic Scale) were used to calculate positive and negative predictive values at varying prevalence levels. Bayesian statistical concepts were employed. RESULTS: At low prevalence or low prior clinical probability, the sensitivity and specificity of the test have little impact on negative predictive value; the tests perform well, with low risk of false negatives. Similarly, at low prevalence or low prior clinical probability, positive predictive values are low regardless of which sensitivity and specificity data are used: the risk of false positives is substantial. CONCLUSIONS: At lower prevalence or prior probabilities, as in the community or primary care setting, these screening tests can rule out bipolarity (when patients have insight into their symptoms), but do not effectively rule it in. Clinicians' estimates of prior probability have as much, or in many cases more, impact on the clinical performance of the bipolar screening tools than the tests' sensitivity and specificity. To improve the performance of screening tools, the primary emphasis needs to be placed on improving clinicians' skill at recognizing clinical and historical features of bipolar diagnosis.

Bayes Theorem↗