Showing papers on "False positive paradox published in 1985"

Immunodiagnosis of sexually transmitted disease.

Abstract: Methods for detecting microbial antigens in clinical specimens offer an alternative to culture in the diagnosis of some sexually transmitted diseases. Developers of the immunologic methods are faced with a number of problems in evaluating the new tests. Traditionally, these tests are compared to culture as the "gold standard." Unfortunately, culture for Neisseria gonorrhoeae or Chlamydia trachomatis--the two agents most commonly sought--is considerably less sensitive than 100 percent. Immunologic methods may appear to produce false positives when the paired specimens are actually false-negative cultures. Another source of discordant results is sampling variation. These considerations, however, will not account for all false-positive results. Even the best non-culture methods have a low rate of false-positive results. If a new test has a specificity of 97 percent, it, by definition, yields approximately 3 percent false-positive reactions. In low-prevalence settings this false-positive rate will create problems in interpreting the results. For example, in a population with 3 percent prevalence of infection, a positive result in a 97 percent specificity test could only have a predictive value of 50 percent. Most testing for STD agents is performed in low-prevalence settings. None of the currently available immunodiagnostic procedures has a performance profile that suggests it will be satisfactory for diagnostic use in the low-prevalence setting.

Epidemiologic evaluation of screening for risk factors: application to genetic screening.

Abstract: To assess the usefulness of screening for risk factors, we derived arithmetic relationships between screening parameters (sensitivity, specificity, and positive predictive value PPV) and risk factor frequency, disease frequency and relative risk. We evaluated these relationships in the special case of genetic markers and disease susceptibility. It can be shown that even in the face of very large relative risks, sensitivity and positive predictive value are affected by the relative magnitude of disease and genetic marker frequencies. When the genetic marker is less frequent than the disease, PPV increases with increasing relative risk but sensitivity remains low. When the genetic marker is more frequent than the disease, sensitivity increases with increasing relative risk but PPV remains low. When marker and disease frequencies are equal, both PPV and sensitivity increase with increasing relative risks, but very high relative risks (greater than 100) have to be obtained for rare diseases. Depending on the goals of the screening program, these relationships can be used to predict the relative magnitudes of false positives (low PPV) and false negatives (low sensitivity). This approach can be generalized to evaluate nongenetic risk factors in screening programs as well.

Rotazyme Assay in Neonates without Diarrhea: Results of Screening Survey and Preliminary Analysis of False Positive Specimens

Abstract: One hundred forty-seven stool specimens from 93 infants younger than four months of age in a Neonatal Intensive Care Unit were tested for rotavirus by the Rotazyme ELISA method (Abbott Laboratories, North Chicago, IL). None of the infants had diarrhea at the time of the testing. Ten of 147 (6.8%) specimens were either low or suspect positive. None had rotavirus by electron microscopy. Excluding the suspect positives, which were negative on retesting, the false positive rate was only 6 of 147 (4.1%). Of five specimens with sufficient material and repeatedly positive tests, heat to 56 degrees C for one-half hour eliminated the binding to the Rotazyme bead but had no effect on the rotavirus positive control. One patient was found to have an extremely high positive Rotazyme test, independently of the survey. No virus was found in this specimen by electron microscopy, and the material responsible for the false positive result was not removed by centrifugation (100,000 X g for one hour), heating to 56 degrees C for one-half hour, trypsin, ether/beta-mercaptoethanol, or dialysis. Thus, false positives were encountered, but the overall rate was acceptably low. Such false positives are likely to result from more than one cause and, depending on results of further study, may be confirmed as false positives by loss of reactivity at 56 degrees C for one-half hour and perhaps lack of binding to a control bead.

Problematic Prostatic Prediction

Abstract: To the Editor.— Chodak and Schoenberg 1 address the important issue of efficacy of prostate cancer screening by digital rectal examination but have mislabeled an important parameter of that test. The authors repeatedly refer to a test "specificity of 29%" erroneously calculated as (true test positives/true test positives+false test positives) and compared it with that reported by others. The value they calculated was really the positive predictive value. The specificity of a test should represent the percentage of negative tests among patients free of disease (true test negatives/true test negatives+false test positives). Unless an appropriate gold standard is available to distinguish those individuals who are truly test negative from those with early undetectable disease (false test negatives), the specificity of a screening test must assume a low disease prevalence with a few false-negatives "contaminating" both the numerator and denominator. The high prevalence in older men of microscopic prostate cancers (almost

Biological false positives to serological tests for syphilis in herpes genitalis.

Abstract: A survey was made of 17 patients (4 females and 13 males) with herpes genitalis who, during period 1971-84, developed biological false positive serological tests for syphilis. Of 121 patients with herpes genitalis diagnosed by herpes culture in 1982-84, 4.1% developed biologically false positive reaction. Duration of symptoms before biologically false positive reaction was 12 days. Duration of false positive reaction was on average 32 days. Eight had borderline reactions, 7 uneven positive titers and 2 serological patterns simulating secondary syphilis.

Misleading false positives

Abstract: haematological findings confirmed a current infection with Epstein-Barr virus producing acute infectious mononucleosis. The diagnosis of infectious mononucleosis was established by clinical, haematological, and serological features, which included the presence of specific antibody to Epstein-Barr virus.2 Advances in virology and immunology now permit us to recognise increasing numbers of diseases caused by Epstein-Barr virus.2 Infectious mononucleosis and appendicitis are two common acute illnesses which affect the same age group. Many primary Epstein-Barr virus infections are probably missed because the full spectrum of illness is not yet known. Although isolation of the virus adds weight to any causal relation based on serological reactions, recovery of Epstein-Barr virus from throat swabs or blood has not yet been attempted on any large group of sick children with ill defined diseases. I suggest that the time has come to look at the relationship of Epstein-Barr virus to appendicitis. B THALAYASINGAM