ROC Curve Construction Research Articles

Sensitivity and Specificity Improvement in Abdominal Obesity Diagnosis Using Cluster Analysis during Waist Circumference Cut-Off Point Selection.

Introduction. The purpose of this study was to analyze the influence of metabolic phenotypes during the construction of ROC curves for waist circumference (WC) cutpoint selection. Materials and Methods. A total of 1,902 subjects of both genders were selected from the Maracaibo City Metabolic Syndrome Prevalence Study database. Two-Step Cluster Analysis (TSCA) was applied to select metabolically healthy and sick men and women. ROC curves were constructed to determine WC cutoff points by gender. Results. Through TSCA, metabolic phenotype predictive variables were selected: HOMA2-IR and HOMA2-βcell for women and HOMA2-IR, HOMA2-βcell, and TAG for men. Subjects were classified as healthy normal weight, metabolically obese normal weight, healthy and metabolically disturbed overweight, and healthy and metabolically disturbed obese. Final WC cutpoints were 91.50 cm for women (93.4% sensitivity, 93.7% specificity) and 98.15 cm for men (96% sensitivity, 99.5% specificity). Conclusions. TSCA in the selection of the groups used in ROC curves construction proved to be an important tool, aiding in the detection of MOWN and MHO which cannot be identified with WC alone. The resulting WC cutpoints were <91.00 cm for women and <98.00 cm for men. Furthermore, anthropometry is insufficient to determine healthiness, and, biochemical analysis is needed to properly filter subjects during classification.

Epidemiologic Behavior and Estimation of an Optimal Cut-Off Point for Homeostasis Model Assessment-2 Insulin Resistance: A Report from a Venezuelan Population.

Background. Mathematical models such as Homeostasis Model Assessment have gained popularity in the evaluation of insulin resistance (IR). The purpose of this study was to estimate the optimal cut-off point for Homeostasis Model Assessment-2 Insulin Resistance (HOMA2-IR) in an adult population of Maracaibo, Venezuela. Methods. Descriptive, cross-sectional study with randomized, multistaged sampling included 2,026 adult individuals. IR was evaluated through HOMA2-IR calculation in 602 metabolically healthy individuals. For cut-off point estimation, two approaches were applied: HOMA2-IR percentile distribution and construction of ROC curves using sensitivity and specificity for selection. Results. HOMA2-IR arithmetic mean for the general population was 2.21 ± 1.42, with 2.18 ± 1.37 for women and 2.23 ± 1.47 for men (P = 0.466). When calculating HOMA2-IR for the healthy reference population, the resulting p75 was 2.00. Using ROC curves, the selected cut-off point was 1.95, with an area under the curve of 0.801, sensibility of 75.3%, and specificity of 72.8%. Conclusions. We propose an optimal cut-off point of 2.00 for HOMA2-IR, offering high sensitivity and specificity, sufficient for proper assessment of IR in the adult population of our city, Maracaibo. The determination of population-specific cut-off points is needed to evaluate risk for public health problems, such as obesity and metabolic syndrome.

PP246-MON: Galactose Oxidation Using C in Healthy and Galactosemic Children

Rationale: This research aimed to assess if the breath test using 13C-galactose can discriminate healthy children from galactosemic children. Methods: Objectives: (1) Set a cut off point for detecting galactosemia through breath test by constructing a ROC curve. (2) Assess the galactose oxidation ability in healthy children. (3) Assess the galactose oxidation ability in galactosemic children. Methodology: Sampling: 21 healthy children and 7 children with galactosemia with age ranging from 1 to 7 years. Breath test: the breath test of all the children was quantitative for CO2 enrichment in exhaled air before and after oral administration of 7mg/kg of 1-13C-Galactose aqueous solution. Samples were collected at baseline time, 30, 60 and 120min after solution administration. Measurement of the CO2 in the air: molar ratio CO2 and CO2 were quantified by the mass/charge ratio (m/z) of stable isotopes through a mass spectrometer in every air sample. Statistical analysis: ROC curve construction in order to determine the best cutting point of differences in percentage of 1-13C-galactose recovered in CO2 that provides a positive breath test for galactosemia detection. Results: Sick children had some percentage of cumulative 13C in the exhaled air from labeled galactose (CUMPCD) ranging from 0.03% in 30 minutes time to 1.67% in 120 minutes. In contrast, healthy subjects showed a CUMPCD much more expressive, with values ranging from 0.4% in 30 minutes to 5.58% in 120 minutes. Conclusion: This study has shown that there is a great difference in galactose oxidation in children with and without galactosemia, hence the breath test is useful in discriminating children with GALT deficiencies. There is no conflict of interest in this study.

PP247-MON: Validation of the Screening Tool for the Assessment of Malnutrition for Use Upon Hospital Admissions in Pediatrics

Rationale: This research aimed to assess if the breath test using 13C-galactose can discriminate healthy children from galactosemic children. Methods: Objectives: (1) Set a cut off point for detecting galactosemia through breath test by constructing a ROC curve. (2) Assess the galactose oxidation ability in healthy children. (3) Assess the galactose oxidation ability in galactosemic children. Methodology: Sampling: 21 healthy children and 7 children with galactosemia with age ranging from 1 to 7 years. Breath test: the breath test of all the children was quantitative for CO2 enrichment in exhaled air before and after oral administration of 7mg/kg of 1-13C-Galactose aqueous solution. Samples were collected at baseline time, 30, 60 and 120min after solution administration. Measurement of the CO2 in the air: molar ratio CO2 and CO2 were quantified by the mass/charge ratio (m/z) of stable isotopes through a mass spectrometer in every air sample. Statistical analysis: ROC curve construction in order to determine the best cutting point of differences in percentage of 1-13C-galactose recovered in CO2 that provides a positive breath test for galactosemia detection. Results: Sick children had some percentage of cumulative 13C in the exhaled air from labeled galactose (CUMPCD) ranging from 0.03% in 30 minutes time to 1.67% in 120 minutes. In contrast, healthy subjects showed a CUMPCD much more expressive, with values ranging from 0.4% in 30 minutes to 5.58% in 120 minutes. Conclusion: This study has shown that there is a great difference in galactose oxidation in children with and without galactosemia, hence the breath test is useful in discriminating children with GALT deficiencies. There is no conflict of interest in this study.

PP248-MON: Validation of a Nutritional Screening Tool for use in Ambulatory Pediatric Setting

Rationale: This research aimed to assess if the breath test using 13C-galactose can discriminate healthy children from galactosemic children. Methods: Objectives: (1) Set a cut off point for detecting galactosemia through breath test by constructing a ROC curve. (2) Assess the galactose oxidation ability in healthy children. (3) Assess the galactose oxidation ability in galactosemic children. Methodology: Sampling: 21 healthy children and 7 children with galactosemia with age ranging from 1 to 7 years. Breath test: the breath test of all the children was quantitative for CO2 enrichment in exhaled air before and after oral administration of 7mg/kg of 1-13C-Galactose aqueous solution. Samples were collected at baseline time, 30, 60 and 120min after solution administration. Measurement of the CO2 in the air: molar ratio CO2 and CO2 were quantified by the mass/charge ratio (m/z) of stable isotopes through a mass spectrometer in every air sample. Statistical analysis: ROC curve construction in order to determine the best cutting point of differences in percentage of 1-13C-galactose recovered in CO2 that provides a positive breath test for galactosemia detection. Results: Sick children had some percentage of cumulative 13C in the exhaled air from labeled galactose (CUMPCD) ranging from 0.03% in 30 minutes time to 1.67% in 120 minutes. In contrast, healthy subjects showed a CUMPCD much more expressive, with values ranging from 0.4% in 30 minutes to 5.58% in 120 minutes. Conclusion: This study has shown that there is a great difference in galactose oxidation in children with and without galactosemia, hence the breath test is useful in discriminating children with GALT deficiencies. There is no conflict of interest in this study.

Construction of ROC curves to assess the value of antisperm antibodies in distinguishing obstructive from nonobstructive azoospermia

Construction of ROC curves to assess the value of antisperm antibodies in distinguishing obstructive from nonobstructive azoospermia

Bone Formation Markers in Adults with Mild Osteogenesis Imperfecta

Plasma concentrations of procollagen peptides are decreased in osteogenesis imperfecta (OI), whereas other bone formation markers may be increased. We examined the utility of combining these markers in the diagnosis of OI in adults. We measured plasma concentrations of procollagen-1 N-peptide (P1NP), osteocalcin, and bone alkaline phosphatase in 24 patients with nondeforming OI, 25 patients with low bone mass due to other causes, and 38 age- and sex-matched controls. The discriminant ability of various test combinations was assessed by the construction of ROC curves. The median (range) ratio of osteocalcin to P1NP was significantly greater in patients with type I OI [1.75 (0.80-3.86)] than in controls [0.59 (0.34-0.90)] and patients with other causes of low bone mass [0.48 (0.05-1.38); P <0.0001]. This ratio allowed nearly complete differentiation between healthy controls and patients with type I OI, but not patients with type IV OI. With a cutoff of 0.97 for osteocalcin:P1NP, the sensitivity and specificity were maximized at 95% (95% CI 76%-100%) and 88% (69%-97%), respectively, for patients with other causes of low bone mass vs those with type I OI only. For patients with other causes of low bone mass vs all OI patients, sensitivity and specificity were 83% (63%-95%) and 88% (69%-97%), respectively. The addition of bone alkaline phosphatase data did not improve the discriminant ability of the osteocalcin:P1NP ratio. The osteocalcin:P1NP ratio is a sensitive and specific test for type I OI in adults, but it has less utility in the diagnosis of other types of nondeforming OI.

ADP-induced platelet aggregation and platelet reactivity index VASP are good predictive markers for clinical outcomes in non-ST elevation acute coronary syndrome

Clopidogrel responsiveness has been proposed to be involved in recurrent ischemic events after stenting for non-ST elevation acute coronary syndromes (NSTE ACS). However, its biological definition is not consensual. We assess the value of ADP-induced platelet aggregation (ADP-Ag) and platelet reactivity index VASP (PRI VASP) in predicting recurrent ischemic events in patients with NSTE ACS undergoing percutaneous coronary intervention (PCI). We studied 195 consecutive NSTE ACS patients undergoing PCI after a 600 mg loading dose of clopidogrel. ADP-Ag and PRI VASP were analysed. The primary end-point was recurrent ischemic events within 30 days of PCI. It occurred in 14 patients (7%). Construction of ROC curves to examine the value of predictive models showed that sensitivity and specificity for primary endpoint were 79% and 76%, respectively, for a maximal intensity of ADP-Ag >or=70%, 93% and 50% for PRIVASP > 53%. The positive and negative predictive values were 21% and 98%, respectively, for ADP-Ag >or=70%, 12% and 99% for PRIVASP > 53%. In patients with NSTE ACS undergoing PCI, ADP-Ag and PRI VASP identify low responders to clopidogrel with an increased risk of recurrent ischemic events with respective cut-off values of 70% and 53%.

Probe tone thresholds in the auditory nerve measured by two-interval forced-choice procedures.

An important goal of auditory physiology is to relate the coding of signals in the auditory nerve to behavioral sensitivity. A useful step towards that goal is to measure physiological thresholds for the detection of tones in the neural spike train that are comparable to psychophysical thresholds. Detectability depends on the variability as well as the mean value of the response. A two-interval forced-choice task provides a criterion-free measure of detectability. On each trial of our experiments a probe tone was taken to be correctly detected if the number of spikes in response to the tone exceeded the number of spikes in an otherwise identical interval that did not contain the probe tone. (Analysis of the pulse-number distributions also allowed construction of ROC curves directly comparable to psychophysical ROC curves.) The proportion of trials that yielded correct detections was measured as a function of stimulus intensity to form a neurometric function, directly comparable to a psychophysical psychometric function. Threshold was defined as the intensity that produced a given proportion correct. The threshold intensity was also measured by an up-down procedure. Agreement between the two measures of threshold was excellent. Using the up-down procedure we could measure threshold in about 1 min, making it practical to measure the thresholds of a single neuron for many conditions. Comparisons of physiological and psychophysical ROC curves and neurometric and psychometric functions show systematic differences indicating that the animal makes its decisions inefficiently, perhaps by basing its decision on the maximum response among many neurons, rather than just the activity of the single most sensitive neuron.

Enhancement of perceptual sensitivity as the result of selectively attending to spatial locations.

The present experiment employed a visual signal-detection task within a cost-benefit (inhibition-facilitation) paradigm to examine the effects of selective attention on perceptual sensitivity. A central cue directed the subjects’ attention to either a right or a left spatial location where a detection task was performed. The cue was either a high/low or neutral-validity indicator of the position in which an event was likely to occur. A rating-scale response scheme in conjunction with the subjects’ target signal locational judgments allowed for the construction of ROC curves for each condition. Significant benefits were found for all subjects, supporting the hypothesis that selective attention can enhance perceptual sensitivity. Deallocation of attention resulted in an inhibition of sensitivity in unattended spatial locations. Subjects were consistently most sensitive in the right spatial location. There were no significant differences in overall response bias among the three conditions or in spatial locations. The results support theories of attention, such as “perceptual tuning, ” that suggest very early selective control.