Number Of False-positive Tests Research Articles

Haemoglobin, haematocrit and red blood cell indices in elite cyclists. Are the control values for blood testing valid?

In international cycling and cross-country skiing competitions, blood tests are used to unmask the performance enhancing misuse of erythropoietin. Haematocrit (cycling) and haemoglobin (cross-country skiing) limits have been set by international sporting federations (haematocrit 50%, haemoglobin 18.5 g/dl). Athletes tested above these cut-off values are declared unfit for competition. To investigate the validity of these regulations, we studied haemoglobin, haematocrit and red blood cell indices of elite cyclists before erythropoietin became commercially available. We investigated 523 blood samples of 92 male elite cyclists (age 16-31 years) from 1978 to 1987. Haematocrit, haemoglobin and red blood cell count were analysed automatically, erythrocyte indices were calculated. Haemoglobin (-0.3 +/- 1 g/dl), haematocrit (-1.2 +/- 2.8%) and red blood cell count (-0.2 +/- 0.4 x 10(6)/mm3) decreased significantly (p < 0.05) with increasing training workload. The erythrocyte indices showed no significant change. Fifty-four blood samples (10.3%) showed a haematocrit above 50%, one sample presented a haemoglobin mass higher than 18.5 g/dl. During periods of increased workload, less athletes tested above the haematocrit limit. The current haematocrit limit used in blood tests might lead to a high number of false positive tests.

Usefulness in predicting coronary artery disease by ultrasonic evaluation of the carotid arteries in asymptomatic hypercholesterolemic patients with positive exercise stress tests

A positive exercise electrocardiogram (ECG) is not infrequent occurrence in asymptomatic hypercholesterolemic patients, but the number of false-positive tests may be relatively high (50%). Therefore, the ability of a positive stress ECG to predict coronary artery lesions is low even in populations with ≥1 cardiovascular risk factors. To increase the diagnostic value of exercise tests for screening asymptomatic individuals, we analyzed whether combined clinical parameters with carotid echography would accurately predict coronary atherosclerotic lesions by coronary angiography in asymptomatic hypercholesterolemic patients with a positive exercise ECG. Seventy-six asymptomatic patients (between 35 and 65 years of age) with hypercholesterolemia (total plasma cholesterol >6.5 mmol/L or 250 mg/dl) and a positive stress ECG were referred for carotid B-mode echography and coronary angiography. Carotid echography data were divided into 2 categories: (1) absence of any atherosclerotic plaque, or (2) presence of ≥1 arterial plaques. Coronary stenosis assessed by coronary angiography was considered to correspond to a ≥50% reduction of coronary lumen diameter. Forty-three patients (57%) displayed coronary lesions; most (38; 88%) had carotid plaque. Multivariate analysis showed that the presence of carotid plaque was significantly associated with coronary stenosis (odds ratio 15.2; confidence interval 5.0 to 54.5). In subgroups characterized by high frequency of false-positive exercise electrocardiographic tests (women and patients with a 10-year predicted risk of coronary artery disease [CAD] <15%), none of the patients without carotid plaque exhibited coronary lesions. Echographic evaluation of carotid plaque (plaque vs no plaque) significantly improved the diagnostic specificity of exercise electrocardiography. We conclude that the combination of clinical, electrical, and echographic data facilitates cost-effective noninvasive detection of CAD in asymptomatic hypercholesterolemic patients.

Is carbohydrate-deficient transferrin in serum useful for detecting excessive alcohol consumption in hypertensive patients?

The aim of this study was to examine the diagnostic usefulness of carbohydrate-deficient transferrin (CDT) in serum in a cross-sectional study of 439 treated hypertensive men. We related the results to alcohol intake by questionnaire and to biochemical and hemodynamic measurements known to reflect excessive alcohol consumption. The diagnostic sensitivity and the specificity for high alcohol intake (> or = 24 g/day of ethanol) were 44% and 87%, respectively. The group with reported high alcohol intake (n = 32) was characterized by hemodynamic and biochemical changes typical of alcohol abuse. The corresponding profile for the patients with increased serum CDT concentrations (n = 70) was different in several respects, indicating a considerable number of false-positive tests. We conclude that serum CDT determination had low sensitivity and specificity for excessive alcohol consumption in this group of hypertensive patients. The results illustrate the importance of evaluating new laboratory methods in unselected patient populations before drawing any conclusions about their clinical value.

The diagnostic value of salivary gland scintigraphy in patients suspected of primary Sjögren's syndrome.

The diagnostic value of salivary gland scintigraphy in patients suspected of having primary Sjögren's syndrome (SS) was studied in 149 consecutive patients who presented with joint and/or muscle complaints in combination with dryness of the mouth and/or eyes and in 20 control subjects. The diagnosis primary SS could be established in 26 of these patients. Salivary gland scintigraphy scored by means of analogue pictures was abnormal in 19 out of 26 patients with primary SS but abnormal scintigrams were also found in 57 of the 123 patients without primary SS and in five of the controls. This resulted in a positive predictive value of an abnormal salivary gland scintigram of 25% and a negative predictive value of a normal investigation of 90%. From the high number of false positive test results in the patient population studied it is concluded that salivary gland scintigraphy has only a limited discriminatory value for the diagnosis of primary SS.

Use of meta-analysis to evaluate tolonium chloride in oral cancer screening

This study used meta-analysis, an analytical technique that uses raw data from previous researchers, to estimate the efficacy of screening for oral cancer with tolonium chloride (TCl). TCl, a vital blue dye, selectively stains acid tissue components such as DNA and RNA and has been used for more than 20 years by surgeons to identify suspected cancerous lesions. It has not been routinely used by dentists to screen either general or high-risk populations. Sensitivity and specificity, as well as positive and negative predictive values for the TCl test, were calculated. Sensitivity of TCl ranged from 97.8% to 93.5%, and specificity ranged from 92.9% to 73.3%. It was determined that if TCl is used to screen high-risk populations, the likelihood of a false negative finding is extremely low, whereas false positive results will be relatively numerous. However, given the high sensitivity of the test, the absolute number of false positive tests will be small. Further analysis is needed to evaluate the economic costs of false positives and false negatives, versus the value of identifying true positives at an early stage.

Mass Screening of Neuroblastoma in Infancy

A vanillylmandelic acid spot test for screening infants for neuroblastoma was developed in cooperation with 11 health centers in Kyoto, Japan. In this system, the parent sends a filter paper spotted with the infant's urine at 6 or 7 months of age. From 78,331 infants screened during the six years from July 1973 to September 1979, four asymptomatic infants with neuroblastoma were discovered. Three of them have already completed their treatments and have recovered. The cost of screening 13,000 infants per year was $7,500. One false-negative test was encountered, as were a number of false-positive tests.

Studies on Media for Enumerating Enterococci in Frozen Vegetables

A study was made of the relative sensitivity and specificity of presumptive and confirmatory media for the most probable number enumeration of enterococci in frozen vegetables. Azide dextrose broth yielded the highest numbers of confirmable enterococci and its sensitivity was shown to be comparable to nonselective media. The use of ethyl violet azide broth as a confirmatory medium resulted in a significant number of false positive tests. Growth in broth containing 6.5% sodium chloride incubated at 45 C for 2 days was found to be a more specific confirmatory test for enterococci.

Studies on Media for Enumerating Enterococci in Frozen Vegetables1

A study was made of the relative sensitivity and specificity of presumptive and confirmatory media for the most probable number enumeration of enterococci in frozen vegetables. Azide dextrose broth yielded the highest numbers of confirmable enterococci and its sensitivity was shown to be comparable to nonselective media. The use of ethyl violet azide broth as a confirmatory medium resulted in a significant number of false positive tests. Growth in broth containing 6.5% sodium chloride incubated at 45 C for 2 days was found to be a more specific confirmatory test for enterococci.