Sensitivity, specificity and predictive value of hearing complaints

This study assessed the sensitivity, specificity and predictive value of hearing complaints in outpatients attending an university ear, nose and throat clinic. A cross-sectional study was carried out in Canoas, Southern Brazil, from 1999 to 2002. Seven-hundred and ninety-five subjects who underwent the audiometric test were analyzed. The results showed that the complaint of hearing loss presented 80.9% sensitivity, 69.6% specificity and 86.5% positive predictive value and 60.4% negative predictive value. Despite its subjective character, the audiometric test can be considered a reliable diagnostic tool and should be used due to its low cost compared to the new technologies.     

Sporadic vs familial classification given etiologic heterogeneity: I. Sensitivity, specificity, and positive and negative predictive value

Environmental factors are etiologically important in many non-Mendelian familial disorders in man. Because such disorders often occur as "sporadic" cases, (ie, an affected individual with no affected relatives), it is tempting to assume that such cases represent an "environmental" form of the disorder. This paper presents an evaluation of the sensitivity, specificity, and positive and negative predictive power (PPV and NPV) of this "sporadic vs familial classification." The model assumes etiologic heterogeneity with a subpopulation of cases due to a "major" environmental event acting independent of genotype and the remaining cases resulting from a generalized single major locus (SML). Sibship size is modeled by a truncated negative binomial distribution. For rare disorders, this classification has high sensitivity and NPV but low specificity and PPV. As the disorder becomes more common, sensitivity and NPV fall while specificity and PPV rise. The power of the method increases substantially with increasing sibship size up to four or five, but further increases in power are minimal. MZ twins add considerable power to the method but aunts and uncles add little if anything. Both a correlational (phi) and an agreement-based (kappa) statistic indicate that, under most realistic circumstances, the relationship between etiology and family history is modest.     

Sensitivity and predictive value positive measurements for public health surveillance systems

Two important measurements for the evaluation of a public health surveillance system are sensitivity and predictive value positive (PVP). The computation of sensitivity and PVP for a public health surveillance system, however, can be complicated by the absence of an appropriate gold standard. In addition, there are few references for the computation of sensitivity and PVP for a surveillance system. To determine how these attributes of evaluation have been reported in epidemiologic literature, I review papers that report sensitivity and PVP for public health surveillance systems. Of the 31 papers that met selection criteria, 21 (68%) included either a reference for the computation or a definition of the attributes, whereas 18 (58%) reported both attributes. All 31 papers reported sensitivity, and among the 31 papers, 24 (77%) reported more than one sensitivity measurement. Among the 18 papers that reported at least PVP, 13 (72%) reported more than one PVP measurement. This review provides guidance in computing sensitivity and PVP for a public health surveillance system.     

Optimal designs of two-stage studies for estimation of sensitivity,specificity and positive predictive value

The cost efficiency of estimation of sensitivity, specificity and positive predictive value from two-stage sampling designs is considered, assuming a relatively cheap test classifies first-stage subjects into several categories and an expensive gold standard is applied at stage two. Simple variance formulae are derived and used to find optimal designs for a given cost ratio. The utility of two-stage designs is measured by the reduction in variances compared with one-stage simple random designs. Separate second-stage design is also compared with proportional allocation (PA). The maximum percentage reductions in variance from two-stage designs for sensitivity, specificity and positive predictive value estimation are P per cent, (1-P) per cent and W, respectively, where P is the population prevalence of disease and W the population percentage of test negatives. The optimum allocation of stage-two resources is not obvious: the optimum proportion of true cases at stage two may even be less than under PA. PA is near optimal for sensitivity estimation in most cases when prevalence is low, but inefficient compared with the optimal scheme for specificity.     

Estimating sensitivity and specificity from positive predictive value, negative predictive value and prevalence: application to surveillance systems for hospital-acquired infections

Sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) are terms usually associated with diagnostic testing. Although these concepts have been expanded from diagnostic assays to surveillance systems, these systems are not like diagnostic assays. In attempting to estimate the sensitivity and specificity of surveillance systems, situations may arise where only the PPV, NPV and prevalence are known. We aim to demonstrate the equivalence of two methods for calculating sensitivity and specificity from PPV, NPV and prevalence. The formulae for sensitivity and specificity are calculated from first principles and compared with the adjustment of a standard contingency table. We have illustrated this method using a review of a sample of surgical site infection cases following coronary artery bypass grafting. The derived prevalence from the sample is an estimate of the population prevalence and is the value that must be used in the formulae for sensitivity and specificity as functions of PPV, NPV and prevalence to obtain the same estimates as those obtained from the adjusted contingency table. The general proof of this principle is provided as an Appendix. The sensitivity and specificity of surveillance systems can be calculated by two equivalent methods when only PPV, NPV and prevalence are known.     

Sensitivity, specificity and predictive values: a graphical approach

The relation between sensitivity, specificity and prevalence is illustrated by means of a graphical device, applied to two diagnostic questions on gastroenteritis in children. The relation between the predictive values and the prevalence is also illustrated graphically.     

The analysis of sensitivity, specificity, positive predictive value and negative predictive value of cold provocation thermography in the objective diagnosis of the hand-arm vibration syndrome

The diagnosis of digital artery vasospasm in the hand-arm vibration syndrome (HAVS) is clinically based, and the need for an accurate objective test to support the diagnosis has been highlighted. This study aims to analyse the potential of cold provocation thermography (CPT) to fulfill this role. CPT was performed on two groups of subjects: 10 controls and 21 patients with Raynaud's phenomenon (RP) secondary to HAVS. After taking a pre-cooling image, patients donned latex gloves and immersed their hands in water at a temperature of 5 degrees C for 1 min. The patients removed their hands from the water and discarded the gloves, and further images were taken every 30 s for 10 min. On each image, the temperatures of the tip and base were analysed for each digit. The sensitivity, specificity, positive and negative predictive values for fingertip temperatures only, fingertip and fingerbase temperatures combined, and fingertip temperature, fingerbase temperature and temperature gradient combined were determined. Patients with RP secondary to HAVS demonstrated significantly lower finger tip and base temperatures and lower digital temperature gradients at all time intervals when compared with controls (P < 0.01, Student's t-test). CPT has good sensitivity, specificity, positive predictive value and negative predictive value; it strongly supports the clinical diagnosis of digital vasospasm.     

The value of basic science in clinical diagnosis: creating coherence among signs and symptoms

BACKGROUND: We investigated whether learning basic science mechanisms may have mnemonic value in helping students remember signs and symptoms, in comparison with learning the relation between symptoms and diagnoses directly. PURPOSE: To compare 2 approaches to learning diagnosis: learning how features of various conditions relate to underlying pathophysiological mechanisms and learning the conditional probabilities of features and diseases. METHODS: Undergraduate students (n = 36) were taught 4 disorders (upper motor neuron lesion, lower motor neuron lesion, neuromuscular junction disease and muscular disease), either using basic science explanations or (symptom x disease) probabilities. They were tested with diagnostic cases immediately after learning and 1 week later. RESULTS: On the immediate test, there was no difference in the results. One week later, the accuracy of the mechanism group remained at 0.52, but the performance of the probability group had dropped to 0.43. CONCLUSIONS: Knowledge of basic science may have value in clinical diagnosis by helping students recall or reconstruct the relationships between features and diagnoses.     

Sensitivity and specificity of recalled vasomotor symptoms in a multiethnic cohort

Many epidemiologic studies include symptom checklists assessing recall of symptoms over a specified time period. Little research exists regarding the congruence of short-term symptom recall with daily self-reporting. The authors assessed the sensitivity and specificity of retrospective reporting of vasomotor symptoms using data from 567 participants in the Study of Women's Health Across the Nation (1997-2002). Daily assessments were considered the "gold standard" for comparison with retrospective vasomotor symptom reporting. Logistic regression was used to identify predictors of sensitivity and specificity for retrospective reporting of any vasomotor symptoms versus none in the past 2 weeks. Sensitivity and specificity were relatively constant over a 3-year period. Sensitivity ranged from 78% to 84% and specificity from 85% to 89%. Sensitivity was lower among women with fewer symptomatic days in the daily assessments and higher among women reporting vasomotor symptoms in the daily assessment on the day of retrospective reporting. Specificity was negatively associated with general symptom awareness and past smoking and was positively associated with routine physical activity and Japanese ethnicity. Because many investigators rely on symptom recall, it is important to evaluate reporting accuracy, which was relatively high for vasomotor symptoms in this study. The approach presented here would be useful for examining other symptoms or behaviors.     

Sensitivity and specificity of clinical case definitions for pertussis

We evaluated the diagnostic performance of 15 clinical case definitions for pertussis in 233 patients who developed acute respiratory illness during community outbreaks in Wisconsin and Delaware. Using results from culture (Regan-Lowe media) and serology (Ig-class-specific ELISA) as diagnostic standards, cough for greater than or equal to 14 days was both sensitive (84 per cent-92 per cent) and specific (63 percent-90 per cent) in identifying patients with pertussis. This definition may be useful in monitoring pertussis outbreaks and for investigating contacts of culture-positive cases.     

The logistic modeling of sensitivity, specificity, and predictive value of a diagnostic test.

A method is described for modeling the sensitivity, specificity, and positive and negative predictive values of a diagnostic test. To model sensitivity and specificity, the dependent variable (Y) is defined to be the dichotomous results of the screening test, and the presence or absence of disease, as defined by the "gold standard", is included as a binary explanatory variable (X1), along with variables used to define the subgroups of interest. The sensitivity of the screening test may then be estimated using logistic regression procedures. Modeled estimates of the specificity and predictive values of the screening test may be similarly derived. Using data from a population-based study of peripheral arterial disease, the authors demonstrated empirically that this method may be useful for obtaining smoothed estimates of sensitivity, specificity, and predictive values. As an extension of this method, an approach to the modeling of the relative sensitivity of two screening tests is described, using data from a study of screening procedures for colorectal disease as an example.     

Sources, symptoms, and signs of arsenic poisoning

Arsenic poisoning continues to be a serious medical problem that may easily be overlooked or misdiagnosed. The broad constellation of symptoms and signs in arsenic poisoning, along with changing sources of this toxin, contributes to misdiagnosis. A re-examination of current potential sources was carried out. Sources were determined in 17 of 20 documented cases of arsenic poisoning. Fourteen cases resulted from ingestion of a single, commonly available, arsenic-containing ant killer. In contrast to earlier reports, this survey found that agricultural and industrial sources were relatively uncommon. A peculiar posturing of the hand is commonly seen in the early stages of arsenic poisoning prior to the development of Mee's lines or palmar hyperkeratosis. An illustrative case is reported that resulted from intermittent self-administration of an arsenic-containing ant killer in order to maintain a state of chronic invalidism.     

Differential cellular reactivity to adult worm antigens of patients with different clinical forms of schistosomiasis mansoni.

Analysis of the proliferation in vitro of peripheral blood mononuclear cells and the production of interferon-gamma (IFN-gamma) in individuals infected with Schistosoma mansoni and showing different clinical forms of the disease, as well as normal putatively immune individuals from an endemic area, was undertaken using total and fractionated soluble adult worm antigens (SWAP). A higher frequency of detectable response to fractionated antigens in T cell Western blot assays was observed in individuals with the more severe forms of the disease. Analysis of variance showed that, in the Western blot assays, there was a statistically significant difference in the level of cellular proliferation to antigens with low molecular weight (less than 21 kDa) between hepatosplenic patients and those with intestinal and hepatointestinal forms of the disease. No correlation between cellular proliferation and IFN-gamma production was observed. Most of the normal individuals from an endemic area failed to show significant proliferative responses to SWAP T cell Western blot assays or to antigen immobilized on nitrocellulose; they did show significant proliferative responses to whole soluble SWAP with positive IFN-gamma production. The results are consistent with the hypothesis that variations in the cellular immune responses to SWAP influence both the development of pathology and resistance to infection in schistosomiasis mansoni.     

Peripheral arterial occlusive disease: prognostic value of signs, symptoms, and the ankle-brachial pressure index.

OBJECTIVES: To determine whether different levels of the ankle-brachial pressure index (ABPI) are associated with an increased risk for progressive limb ischemia, nonfatal and fatal cardiovascular events. To investigate the prognostic value of signs and symptoms associated with peripheral arterial occlusive disease (PAOD). DESIGN: Prospective follow-up study. SETTING: Eighteen general practice centers in the Netherlands. PARTICIPANTS: Three thousand six hundred forty-nine participants (53% female) with a mean age of 59 years (range: 40-78 years). MAIN OUTCOME MEASURES: Progressive limb ischemia, cardiovascular morbidity and mortality. RESULTS: At baseline, 458 participants had PAOD, defined as an ABPI < 0.95. Among these, 148 (32.2%) had an ABPI < 0.70. Cox proportional hazards models showed that after a mean follow-up period of 7.2 years, PAOD patients with an ABPI < 0.70 were at higher risk for cardiovascular death, compared with participants with a moderately reduced ABPI (< 0.95 - > or = 0.70): HR 2.3 versus 1.2. Older age, complaints of intermittent claudication, abnormal pedal pulses, elevated blood pressure, and coexisting cardiovascular disease at baseline were also significant independent prognostic factors for one or more of the adverse outcome events in these patients. CONCLUSION: The ABPI is inversely associated with cardiovascular mortality in PAOD patients. A low ABPI is an independent predictor for cardiovascular mortality in PAOD patients.