Multiple diagnostic tools are used by emergency physicians, every day. In addition, new tools are evaluated to obtain more accurate methods and reduce time or cost of conventional ones. In the previous parts of this educational series, we described diagnostic performance characteristics of diagnostic tests including sensitivity, specificity, positive and negative predictive values, and likelihood ratios. The receiver operating characteristics (ROC) curve is a graphical presentation of screening characteristics. ROC curve is used to determine the best cutoff point and compare two or more tests or observers by measuring the area under the curve (AUC). In this part of our educational series, we explain ROC curve and two methods to determine the best cutoff value.

Background: Limited research has been conducted on the role of ultrasound in predicting difficult laryngoscopy (DL). This study aimed to evaluate the predictive values of upper airway ultrasound parameters for the degree of DL during intubation. Materials and Methods: This observational-prospective study was performed on 120 patients requiring intubation during elective surgery. Initially, the degree of DL was assessed by the Mallampati Scale. The patient's neck circumference was then measured and recorded. Ultrasound was used to determine the hyomental distance in the neutral position (HMDN), the head extension (HMDE), as well as tongue width (TW), tongue thickness (TT), oral cavity height ratio (OCH), the amount of soft tissue (ST), and the Tongue thickness-to-oral cavity height ratio (TT/OCH). Afterward, the patients underwent general anesthesia and were intubated. The degree of difficult intubation was measured based on the Cormack-Lehane classification system. The patients were divided into easy and difficult laryngoscopy groups. Finally, the effectiveness of the two methods of ultrasound and intubation was compared. Results: The Cormack score and Mallampati class recorded intubation difficulty as 28. 3% and 30. 8%, respectively. According to the Cormack score, only the neck circumference was significantly associated with intubation difficulty (P=0. 002). Regarding Mallampati class, the neck circumference and HMDN, HMDE, TT, OCH, and ST were significantly associated with DL (P <0. 05). The numerical value of the area under the curve (AUC) in the receiver operating characteristic (ROC) curve for sonographic parameters based on the Cormack score and Mallampati scoring system was poor (AUC <0. 7). Conclusion: The results showed that the accuracy of ultrasound criteria in predicting the severity of intubation with laryngoscopy is poor.

Objective: Obesity is a major public health concern and there are different ways to detect it in population. The aim of the present study is to evaluate the neck circumference (NC) in a simple and practical way. Materials and Methods: This cross-sectional survey utilized data from the Yazd Health Study (YaHS) which is a population-based cohort study. In brief, 9962 individuals aged 20-70 years with measurement of body weight, height, waist circumference (WC) and NC were available for analysis. To determine the relationship between NC and other anthropometric measurement, we utilized of Pearson's correlation coefficient. Receiver operator characteristic (ROC) curve analysis was used to find out an optimal cut off value for detecting general and central obesity as well as to determine the sensitivity and specificity of NC in predicting general and central obesity. The whole analysis was performed using SPSS version 22. Results: NC correlated positively with body mass index (BMI) (r= 0. 608, P< 0. 001 in men and r= 0. 541, P< 0. 001 in women) and WC (r= 0. 662, P< 0. 001 in men and r= 0. 542, P< 0. 001 in women). The best cut-off point for NC to determine people with general obesity was 40. 25 cm for men and 35. 75 cm for women. Conclusion: The NC has an acceptable correlation with BMI and WC. In addition, NC is a simple free measurement which may be utilized in various health-care settings. These properties make the NC as the best anthropometrics to determine overweight and obesity and it can be used as an appropriate predictor for overweight and obesity in population-based screening programs.

Background: Metabolic syndrome (MetS) is a collection of various interrelated risk factors that appear to have an impact as development of atherosclerotic cardiovascular disease (CVDs). Epidemic of childhood and adolescent’ s obesity has increased interest in the metabolic syndrome (MS) due to the potential projection into adulthood. The prevalence of MS in adolescents has been estimated to be 6. 7% in young adults and 4. 2% in adolescents. We aimed to study the MetS in children and adolescents with respect to metabolic changes. Methods: The international Diabetes Federation criteria were used for the selection of cases. Serum paraoxonase 1 (PON1) activities were measured using spectrophotometer. Statistical analysis was done using MyStat statistical software. Results: Serum PON1 arylesterase (ARE) and lactonase (LACT) activities were found to be reduced significantly in patients with MetS than in controls. Regression analysis showed a significant correlation between PON1 activities and body mass index. Area under curve (AUC) found to increase from HDL to PON1 ARE to PON1 LACT. Conclusions: From the present study, it is clear that in children and adolescents, reduction in PON1 activities in MetS is mainly due either to abnormalities with synthesis or secretion of HDL cholesterol or oxidative stress as a consequence of excess production of the free radicals. This study also iterates that it is the quality and not the quantity of HDL cholesterol which is important while studying the pathophysiology of MetS.

Background: The objective of this study was to compare various lipid ratios for detection of metabolic syndrome (MetS) in the Iranian general population. Methods: This cross-sectional study involved 5677 subjects aged ≥ 18 years from the general population in Kerman, Iran. Associations between lipid ratio quartiles and MetS were analyzed using logistic regression models. The areas under receiver operating characteristic (ROC) was calculated to determine the accuracy of lipid ratios in predicting MetS. Results: The adjusted chance of having MetS across quartiles of all lipid ratios had an increasing significant pattern (P < 0. 0001). The area under the curves of triglyceride/high-density-lipoprotein-cholesterol (TG/HDL-C) ratio was 0. 85 (95% CI = 0. 84– 0. 87) in men and 0. 85 (95% CI = 0. 84– 0. 86) in women, of total cholesterol (TC)/HDL-C ratio was 0. 79 (95% CI = 0. 77– 0. 81) in men and 0. 79 (95% CI = 0. 77– 0. 81) in women and of low-density-lipoprotein cholesterol (LDL-C)/HDL-C ratio was 0. 73 (95% CI = 0. 71– 0. 75) in men and 0. 74 (95% CI = 0. 72– 0. 76) in women. Conclusion: Our results indicate that the TG/HDL-C Ratio is a better marker than the LDL-C/HDL-C ratio and the TC/HDL-C ratio for identifying MetS in the Iranian population and could be used in clinical practice.