Number Of False-positive Results Research Articles

Drug-nutrient interactions and their implications for safety evaluations

In order to assess the relevance of the drug-nutrient interactions described in this chapter to routine toxicologic studies, the range of nutrient concentrations within which these interactions may occur must be compared to the range of nutrient concentrations found in routinely used rodent diets. While obviously deficient levels of some nutrients were supplied to demonstrate some of the interactions, others occur when the nutrients are present in adequate or excess levels, such as might be found in commercially available diets. These diets are known to vary from batch to batch in nutrient content. A lifetime toxicity/carcinogenicity bioassay using rodents may last longer than 2 years, during which time several batches of diet will be used. The variation in diet composition, coupled with inadequate diet description, makes nutrient-toxin interactions not only possible, but difficult to recognize. These considerations raise the practical and philosophical question as to what type of diet is most appropriate for rodents used for safety evaluation of drugs and chemicals. Is it appropriate to use diets that vary unpredictably in nutrient content, that infer a degree of protection against chemical carcinogenesis and which supply some nutrients such as protein in great excess of dietary needs? Is the increase in sensitivity to chemical carcinogens of animals fed purified diets desirable or does this increased sensitivity of the bioassay exceed that required to assess the risk of human exposure? In other words, is the use of purified diets likely to increase the number of false positive results? Proper interpretation and extrapolation of safety evaluation studies requires adequate description of the test system. Given the profound influence of diet on the response to some toxins, the composition of the diet should, ideally, be defined with the same rigor as are the test compound and the strain, age, sex, and housing conditions of the animals. It is likely, however, that natural ingredients diets will continue to be the diets of choice in safety evaluation studies. This is largely due to economic reasons. It is possible, however, to use these diets with greater confidence if open-formula diets are used and the concentration of each nutrient is reported. Consideration should also be given to preparing diets for use in adult and aging rodents, diets in which protein content is reduced.(ABSTRACT TRUNCATED AT 400 WORDS)

THE GRANULOMA POUCH ASSAY

Chemicals to which man is potentially exposed or that are already distributed in the environment are tested for their mutagenic activity in simple, inexpensive screening tests utilizing prokaryotic and/or eukaryotic cells. These phase I or tier I tests should have a low potential to produce false negative results. This is often achieved by the acceptance of a certain number of false positive results. Therefore chemicals that show positive, contradictory, or inconclusive results in this battery of tier I tests and are still of importance should be further tested in phase II (tier II) tests to provide a broader basis on which risk assessment can be made.

Dexamethasone Suppression Test: Technique and Accuracy

To the Editor. —The dexamethasone suppression test (DST) is of great current interest in psychiatry because of the large body of evidence that some depressed patients fail to suppress cortisol levels to 5 μg/dL or less after an oral dose of 1.0 mg of dexamethasone. 1 Many psychiatrists have adopted this procedure as the first laboratory test of significance for clinical practice. Carroll et al pointed out a number of pitfalls in applying this test. 1 We wish to call attention to the need to assess rigorously the method of cortisol determination used by the clinical laboratories that carry out the test. Routine application of the 5-μg/dL cutoff could lead to a number of false-positive results, based on the results to be described. Research laboratories, eg, those of Carroll, Sachar, and ourselves, use the competitive protein-binding assay (CPBA) method to measure plasma cortisol levels, whereas most clinical laboratories use commercial radioimmunoassay (RIA)kits.

The development of fetal acidosis in the presence of an abnormal fetal heart rate tracing: I. The average for gestational age fetus

An abnormal fetal heart rate (FHR) tracing is a sensitive indicator of positivity that disease exists, but the intrinsic predictive value of such a tracing is disappointingly low because of the large number of false positive results. Abnormal FHR tracings, defined as those having a persistent quantitative score of 4 or less, were measured against time and outcome. A baseline fetal scalp blood sample was taken. Twenty fetuses were acidotic at the first blood samle. There were 121 study cases, all of which were ≥37 weeks' gestational age. All fetuses were average for gestational age. Amniotic fluid was clear, internal FHR tracings were initially normal, and the first pH was normal. A relative acidosis-free interval could be demonstrated during the first 90 to 100 minutes. Following this time period rapid cumulative acidosis was seen, which varied according to the FHR pattern observed. The P50 acidosis values for various patterns were late decelerations, 115 minutes; variable decelerations, 145 minutes; and flat line tracings, 185 minutes.

Meconium screening for cystic fibrosis. An eight-year follow-up study.

The results of more than eight years of screening for cystic fibrosis (CF), utilizing the albumin concentration in meconium, are reported. Over 28 000 meconium samples were tested, over 24 000 of them by the Boehringer-Mannheim strip test, and all samples considered as showing a trace or positive result were followed up by an immunological technique. Eight-three meconium samples contained more than 20 g albumin/kg dry weight meconium and five of these were from children who were found to have CF. One child with CF was missed in the screening. From these figures the sensitivity of the method for detecting CF children at birth was calculated to be 75%, the specificity 99.7%, the negative predictive value 100%, the positive predictive value 4.0% and the incidence of CF in Sweden about 1:4,500. The incidence of pathologically elevated meconium albumin concentrations was found to be 25 times higher in premature than in full-term infants. Since the number of false positive results creates a problem, we suggest that premature children (birth weight less than 2500 g) and newborns with melaena should be excluded from further follow-up studies.

Pulsed doppler echocardiography in diagnosis of pulmonary regurgitation: Its value and limitations

Ninety-eight patients were studied with two dimensional echocardiography combined with pulsed Doppler echocardiography to assess the usefulness and limitations of the Doppler technique in the diagnosis of pulmonary regurgitation. The diagnosis of pulmonary regurgitation by pulsed Doppler echocardiography depended on subjective interpretation of the audio signal and objective interpretation of the time interval histogram for the presence of wide frequency dispersion. During cardiac catheterization in 53 of the 98 patients, indocyanine green was injected into the pulmonary artery, and simultaneous sampling was performed from the right ventricle and femoral artery to diagnose pulmonary regurgitation. Pulmonary regurgitation was confirmed by pulmonary arteriogram in one patient. Among 62 patients with adequate pulsed Doppler echocardiographic studies, diastolic turbulence was noted in 21. When diastolic turbulence was less than 50 percent of the period of diastole, no pulmonary regurgitation was demonstrated in patients studied by indicator-dilution technique. However, three of the four patients with diastolic turbulence greater than 50 percent had positive evidence of pulmonary regurgitation. Audio output was more sensitive than the time interval histogram, and only five patients' findings suggested pulmonary regurgitation. Three of these patients underwent dye-dilution studies; two studies were positive for pulmonary regurgitation and one was negative. Thus, interpretation of pulmonary regurgitation based on the time interval histogram alone produces a large number of false positive results. When diastolic turbulence is greater than 50 percent of the period of diastole, both the sensitivity and specificity of diagnosis of pulmonary regurgitation are increased. Combining audio output and the time interval histogram results in improved diagnostic capability.

Sensitivity, Specificity, and Predictive Accuracy as Measures of Efficacy of Diagnostic Tests

ABSTRACT The proliferation of new tests based on sophisticated technology has given impetus to critical evaluation of the role of clinical decision making. In this presentation selected aspects of ...

Evaluation of antibody inhibition assays of melanoma antigens in sera to monitor tumor growth in melanoma patients

It was reported previously that melanoma leukocyte-dependent antibody (LDA) in the sera of melanoma patients was inhibited by small-molecular-weight (small-mol.-wt.) glycoproteins which were similar to cell surface antigens identified in cell membrane extracts of melanoma cells. The present study was to determine whether measurement of the levels of these factors in sera may be a useful monitor of tumor growth in melanoma patients. Small-mol.-wt. fractions were obtained by gel filtration or membrane chromatography of acidified sera and tested for their ability to inhibit LDA in 51Cr release cytotoxic assays. A panel of LDA was used, consisting of three antisera from melanoma patients, which appeared relatively specific for melanoma, and three non-melanoma antisera against carcinoembryonic antigen, β2 microglobulin, and fetal antigens. The results showed that in patients with melanoma, approximately 70% had melanoma LDA-inhibitory activity detected in the small-mol.-wt. fractions of their sera when these were tested against the panel of melanoma LDA. The specificity of the inhibitory activity for melanoma LDA was shown by failure of the serum fractions to inhibit non-melanoma LDA and by absence of inhibitory activity in equivalent serum fractions from non-melanoma carcinoma patients for melanoma LDA. The levels of melanoma LDA-inhibitory activity in the serum fractions appeared to correlate with tumor growth, as shown by clearance of the inhibitory activity after surgical removal of melanoma and reappearance in the serum of patients who subsequently developed recurrent melanoma. The 30% false-negative rate indicated that the assays could not be used to reliably exclude melanoma, but the close correlation with tumor growth and the low number of false-positive results suggested that in 70% of patients detection of these small-mol.-wt. antigens would be of value to detect recurrence from melanoma and to monitor the effectiveness of therapy.

Specificity of the EMIT drug abuse urine assay methods.

A investigation was conducted to determine the specificity of the EMIT DAU method of drugs of abuse analysis. Drug-free urine, from healthy volunteers, was individually spiked at 1000, 100, 10, and 1 microgram/mL concentrations with each of 162 different drug substances. These spiked samples were analyzed with the EMIT DAU assay for amphetamines, barbiturates, benzodiazepine metabolites, cocaine metabolites, methadone, opiates, and propoxyphene. Although several of the test methods yielded positive results at a concentration of 100 micrograms/mL, many drugs will probably not reach that concentration in the urine. The number of drugs giving a false positive at a concentration of 100 micrograms/mL was very low. The assay for cocaine metabolites gave no false positive results at any of the concentrations studied while the assay for methadone gave the largest number of false positive results. When interpreting the results of this investigation one must consider that in many cases drug metabolites will exist in the urine, salt forms of the drugs studied were used, and ionic strength and pH effects can interfere with the lysozyme enzyme system used in the EMIT DAU assays. In summary, the proper utilization of specificity information may assist the analyst in explaining unusual values obtained in the laboratory, particularly when the subject is concurrently using prescription or nonprescription medication.

Current experience with radioimmunoassay techniques for prostatic acid phosphatase.

Data are presented demonstrating that radioimmunoassay techniques for measurement of serum prostatic acid phosphatase are more sensitive than enzymatic methods in the detection of all stages of prostatic cancer. The possibility of using a solid phase RIA technique to screen for prostatic cancer is considered. Sixty-three hundred and twenty men over age 45 entering a clinical laboratory for any indication were evaluated using the RIA test for PAP. In this group 444 (7%) had elevated test values. Clinical recall and urologic review of the patients with elevated test results yielded 67 who were suspect for prostatic cancer, of whom 59 (88%) were confirmed by prostatic needle biopsy. These data suggest that the RIA for prostatic acid phosphatase as an isolated clinical procedure is not sufficiently specific to be used for screening due to the large number of false-positive results. However, the RIA-PAP test in combination with a follow-up urologic examination is quite specific and deserves further consideration as a screening method for prostatic malignancy.

Neonatal screening for hypothyroïdism by simultaneous determination of T4 and TSH on filter paper

A simultaneous determination of T4 and TSH has been done on 53.000 new borns since January 1st of 1977 in the Midi-Pyrénées district. 18 cases of hypothyroïdism have been detected, an incidence of 1/2950 new borns. TSH values always were above 80 μU/ml ; T4 values are under m -2 σ in 14 cases, normal in 2 cases (8,8 and 9 μg/dl) and between -1 and -2 σ in 2 cases. A thyroid scanning with 123 iodine or 99 Tech. has shown the absence of thyroid in 8 cases, an ectopic gland in 8 cases and a thyroid in a normal position in one case. A treatment has been possible before the first month of life in each case. The average D.Q. for the seven oldest new borns (m = 11 months) is 96. The simultaneous determination of T4 and TSH is a sensitive and specific screening method for hypothyroidism. False-negative are avoided and the number of false-positive results is reduced. All cases of hypothyroidism can be detected (primary hypothyroïdism, hypothalamo-hypopituitary hypothyroïdism, TBG deficiency, etc. . .). Then, an early and certain diagnosis is made possible (T4 low and TSH increased).

Maternal serum alpha-fetoprotein screening: Promise not yet fulfilled

Measurement of alpha fetoprotein (AFP) levels in amniotic fluid has been used as a diagnostic tool for detection of neural tube defects (NTDs) in the fetus. AFP measurement in conjunction with ultrasonography yields a 90% NTD detection rate. The technique is recommended for use in pregnancies known to be at risk of NTDs and as a screening technique for use with 2nd-trimester amniocentesis. In recent years, maternal serum AFP assays have been used for NTD detection. The technique has promise as a diagnostic tool but is not recommended for routine maternal screening. Problems with maternal AFP screening are: 1) the large number of false positive results; 2) lack of general patient and physician education on the screening technique; 3) technical problems related to the assay; 4) inconsistency of assay results from 1 laboratory to another; and 5) the lack of established normal standards for the test.

Further study of fibrinogen degradation products in bladder cancer detection

A new, rapid immunoassay kit for assaying fibrinogen degradation products (FDP) was studied in 56 patients with cancer of the bladder and in 48 control patients. The specificity of the kit was demonstrated with a small number of false positive results. In bladder cancer patients with low-stage, small superficial tumors, FDP was positive in 32.2 per cent. The combination of urinary cytologic examination with FDP increased the accuracy of the positive results to 80 per cent. The rapid FDP test supplements the urinary cytology in the follow-up and detection of early bladder cancer.

Increasing the predictive value positive of the precipitin test for the diagnosis of deep-seated candidiasis.

Three hundred fifty human sera were tested by double immunodiffusion, crossed-line electrophoresis, and crossed immuno-affinoelectrophoresis with a concanavalin A intermediate gel for precipitating antibodies to antigens present in cytoplasmic extracts of Candida albicans. Sera from 48 of 287 hospitalized patients at risk of invasive candidiasis contained precipitating antibodies to Candida antigens. Of these 48 sera, 27 had precipitating antibodies only to cell-wall antigens present in the cytoplasmic extract, and 21 sera had precipitating antibodies to both cytoplasmic and cell-wall antigens. The latter sera came from patients who were 2.5 times as likely to have deep-seated candidiasis as those patients with precipitins exclusively to cell-wall antigens. Sera from seven of 22 patients with vaginal candidiasis and 10 of 41 patients with other fungal infections had precipitating antibodies to C. albicans cell-wall antigens; only two of these sera also contained precipitating antibodies to the cytoplasmic antigens. Crossed immunoaffinoelectrophoresis with concanavalin A reduced the number of false-positive results and increased the predictive value positive of the precipitin test for deep-seated candidiasis from 31% to 71%.

Evaluation of candida precipitin and agglutinin tests for the diagnosis of systemic candidiasis in burn patients

Candida agglutinin and precipitin tests were performed on a group of burned patients without evidence of systemic candidiasis to determine whether tests could be used to distinguish between colonization and systemic disease, as has recently been reported. There were considerable numbers of false-positive results using both tests. These false-positive results occurred regardless of the candida colonization status of the patient. We conclude that these tests are of little diagnostic value in burn patients.

Value of Urinary Simple Phenol and Indican Determinations in the Diagnosis of the Stagnant Loop Syndrome

The urinary excretion of phenol, p-cresol, and indican was determined in 7 patients with the stagnant loop syndrome, 26 patients with coeliac disease, chronic pancreatitis, and partial gastrectomy, and 18 control patients. The mean excretion of the compounds in the patients with the stagnant loop syndrome and in the control patients, respectively, was 77 and 2.3 mg/24 h of phenol (p less than 0.05), 164 and 39.5 mg/24 h of p-cresol (n.s.), and 369 and 41.5 mg/24 h of indican (p less than 0.01). When applied as diagnostic tests for the stagnant loop syndrome, the phenol excretion showed 2 false negative results, the p-cresol excretion 3 false negative and 2 false positive results, and the indican excretion 6 false positive results. The combined use of phenol and indican determinations eliminated the number of false positive results with the indican test, and was found most useful as screening procedure. Determination of phenol and indican in a 24-hour urine sample is likely to provide a simple method for selecting patients with signs of abnormal bacterial colonization in the small intestine for more detailed investigations.

Elimination par la chaleur des fausses réactions positives lors de la détection de l'antigène Australie par les tests d'hémagglutination passive

The detection of the HB'S Antigen by a reversed passive haemagglutination test (Hépanosticon) in sera previously heated at 56 degrees C for 30 mn, is simple and rapid but gives a relatively high number of false positive results. A simple technique is suggested by heating sera betwen 68 degrees C and 80 degrees C and then by centrifugation at 1.500 g for 15 mn, to eliminate these false positive results. The supernatants are tested in the Hepanosticon technique and only the true positive samples, cheked for specificity by other techniques namely radioimmuno assay (R.I.A.) remain positive. Further research is pursued to confirm these first data and to define the exact degree of sensibility of this technique.

The indirect fluorescent antibody test for the detection of circulating antibodies in bovine tuberculosis.

Indirect fluorescent antibody (IFA) tests were carried out on a total of 545 individual serums from beef cattle just before tuberculin testing, using specific FITC-anti-bovine IgG and IgM conjugates. Phenol-killed M. tuberculosis (H37Rv strain) or field strains of M. bovis and M. avium were used as antigenic substrates. All cattle were examined at abattoirs for the presence of tuberculous lesions. A statistically significant difference (p less than 0.001) was found between the number of cattle with serums containing IgM and those with IgG antibody to M. bovis. The majority of cross-reactions that occurred with M. avium was due to IgM antibody. The IFA test using M. bovis and both antiglobulin conjugates detected 77% of cattle with visible lesions of tuberculosis, while the single intradermal caudal fold tuberculin test detected 83%. The IFA test detected 25 of 31 cattle with lesions that failed to react in the tuberculin test. The tuberculin test gave apparently false positive reactions in 6.2% and the IFA test gave false positive reactions in 21.2% of all cattle. The IFA test is of potential use as a further aid in the detection of tuberculous cattle that fail to react to tuberculin. It offers no advantage over the tuberculin test for the detection of all forms of the disease because it fails to detect a significant proportion of tuberculous cattle and produces an unacceptably high number of false positive results.

Urinary glucose unreliable as test for urinary tract infection in infancy.

We tested the reliability of a paper strip test for urinary glucose in the diagnosis of urinary tract infection in babies. Though the number of false positive results (0·7%) was acceptable, 36% false negative results was regarded as unsatisfactory for a screening test for urinary tract infection, and its use cannot be recommended in this age group. This finding, however, is applicable only to urines collected from infants and in no way reflects upon the merits of the test when used in older children or adults.

Experiences with a screening test for bacteriuria.

A comparison of the Testuria “mini-culture” method with a conventional quantitative cultural technic for determining bacteriuria has revealed that most patients with bacteriuria attending a urology outpatient clinic could be detected. The sensitivity approached or exceeded the 90% level. The predictive value was more than 95% for the negatives and still more than 60% for the positives in specimens with more than 100,000 bacteria per ml. When the Testuria “miniculture” method was used in a mass screening program the reliability changed. When the number of bacteria present was low, Testuria gave a greater number of false positive results. The specificity of 92% at the 50,000 and 60.6% at the 100,000 levels of bacteria per milliliter indicates that approximately 10% of the population screened required follow-up studies even though their specimens did not actually exceed these limits. Below the level of 50,000 bacteria per ml., the sensitivity of the Testuria method dropped to 66.8%, which is unacceptable for a screening test at that level. Testuria results correlated well with conventional methods when the number of bacteria was high, as is usually found in patients attending a urology outpatient clinic, but when the number of bacteria was low, Testuria gave a greater number of false positive results than did conventional urine culture technics.