Clinical Value Of The Optimal Operating Point Of ROC Curve For Diagnosis Of Fatty Liver Disease

Objective and backgroundNowadays people enjoy less and less activities because of modern life style and are unaware of the resulting poor health issues . Unhealthy diets which contain high calorific, higher fat, high protein and low fibre lead to obesity. By contrast losing weight and malnutrition, have enhanced the incidence of fatty liver disease. Fatty liver disease is distributed over the World including all ethnic groups and the individual at all levels. It has influenced 10%-30% of the population. The average of incidence is 20%, and the prevalence of the disease is increasing yearly. The incidence in China is lower than in Western countries, but is rising remarkably. Liver biopsy is a "gold standard" to diagnosis the disease, which clearly shows the fat of the shape, distribution, location, range, extent and development of steatosis in the liver cells. The procedure is not always accepted by patients because it is a diagnosis measure with surgical injury. There have been many studies to quantitative diagnosis of fatty liver in CT and MRI in overseas and China. It is still difficult to be popularized because the price is too expensive. The ultrasonograph inspection has certain specificity and the sensitivity to the diagnosis of fatty liver, and has become first method to diagnose the fatty liver disease in overseas and China. Because the developing process of fatty liver disease is slow and asymptomatic, the coverage rate of the ultrasonograph diagnosis to fatty liver is lower than the incidence of fatty liver disease. At the same time, the people lack the recognization to the harmfulness of the fatty liver disease, which limit the individual suffered from fatty liver disease to be picked out.How to enhance the diagnosis rate of fatty liver disease ? It is reported from overseas that they made the preliminary diagnosis with fatty liver index, or predicated the progress of liver fibrosis with the Steato Test that is a simple, non-invasive, and reliable quantitative measure of liver steatosis . To enhance the diagnosis rate, it is inevitable to search for a diagnosis method which is convenient,cheap, non-injury, easy to be operated by doctors and easy to be accepted by patients.The aim of this study was to identify a diagnosis method which could enhance the diagnosis level, to provide the diagnosis proof for the diagnosis of fatty liver disease in early stage, to promote patients to accept further examination and treatment in early stage, to decline the incidence of the disease, to improve the quality of life and to prolong the lifespan of the patients who suffered from fatty liver disease.Method1. To define the risk factors of fatty liver: According to the investigating reports from China and overseas to the risk factors of fatty liver, we selected following these factors which were regard as risk factors of fatty liver, such as age, body height, body weight, body mass index, blood pressure, blood sugar, triglyceride, high density lipoprotein cholesterol, low density lipoprotein cholesterol, very low-density-lipoprotein cholesterol, total cholesterol, alanine aminotransferase, aspartate amino-transferese, and alkaline phosphatase, aspartate aminotransferese/ alanine aminotransferase, total protein, Ablumin, Globulin, Ablumin/ Globulin, et al.2. To select the research subjects and the method: randomly selected people who received the health examination from international health care center in our hospital from September to November in 2006. 551 people have been examined, including 361 males and 190 females. The age is from 19 to 81 year. The subjects were divided into three groups according to the ultrasonography diagnosis: a fatty liver group, a non-fatty liver group and a tendency for fatty liver group. They received physical examination and laboratory test.3. The statistics First to discriminate the syndrome factors to the risk factors of fatty liver (incliding analyse variance and Fisher's liner discriminantion et al), and pick the important factors out; Then, using specificity and sensibility of the receiver operating characteristics curve to evaluate the risk factors of fatty liver, and to find out the diagnostic point of fatty liver, which is very strong specificity and sensibility to fatty liver, to confirm the result is correct of the clinical value of the optimal operating point of ROC curve for diagnosis of fatty liver disease.Result1. The result of the analysis of variance show: the variables of age, body height, body weight, bodymass index , blood pressure, triglyceride, high density lipoprotein cholesterol, low density lipoprotein cholesterol, very-density-lipoprotein cholesterol, total cholesterol, total protein, alanine aminotransferase, aspartate aminotransferese, alkaline phosphatase may useful to discriminate the functions between groups.2. By assessing remarkably to the Eigenvalues of two discrimination functions abstracted, the result show that the two discrimination functions are significant(P<0.05), and are affected by the factors listed below:Zfuncl=0.707 × body mass index+0.188× blood sugar+0.110× Alanine aminotransferase—0.202× Aspartate aminotransferese/Alanine aminotransferase+0.395 × Very-density-lipoprotein cholesterol Zfunc2=-0.624 X body mass index+0.434 X blood sugar+0.735 × Alanine aminotransferase+0.129× Aspartate aminotransferese/Alanine aminotransferase+0.305 × Very-density-lipoprotein cholesterol;3. The discrimination of fisher liner discrimination functions demonstrate that there is the biggest distance between the fatty liver group and the non-fatty liver group, which is easy to be discriminated . The distance between the fatty liver group and the tendency of fatty liver group, the non-fatty liver and the tendency of fatty liver group is small, which is not easy to be discriminated. The discrimination results show that the correct rate of the fatty liver group is 77.4%.; The correct rate of the non -fatty liver group is 94.2%; and the correct rate of the tendency of fatty liver group is 6.3%.4. By assessing the main risk factors of fatty liver using the ROC curve, we found that the significant factors to diagnose of fatty liver disease are body weight, body mass index, alanine aminotransferase, aspartate aminotransferese, triglyceride and the very density lipoprotein cholesterol. The proportion of square meter of above factors under ROC curve in order is: 0.916, 0.872, 0.868, 0.858, 0.833, and0.799. The sensitivity of above factors under ROC curve is 91%, 89%, 90%, 91%, 91%,and85% , respectively. The specificity of above factors under ROC curve is 78%,62%, 66%, 64%,62%, and61%, respectively. The diagnostic point to the fatty liver of above factors under ROC curve is 23.9Kg/m~2, 66.5Kg, 20.5IU/L, 1.28mmol/L, 0.69mmo/L and 24.5IU/L, respectively.5. Assessing the risk factors of the tendency of fatty liver by the ROC curve, we found that the significant factors to diagnosis of the tendency fatty liver disease are body weight, body mass index, Alanine aminotransferase, Aspartate aminotransferese, Triglyceride, Very density lipoprotein cholesterol. The proportion of square meter of above factors under ROC curve in order is 0.864,0.815,0.770, 0.703, 0.689, and0.640. The sensitivity of above factors under ROC curve is 94%, 83%, 78%, 78%, 73% and72%, respectively. The specificity of above factors under ROC curve is 66%,64%,61%, 68%, 62% and63%, respectively. The diagnostic point to the fatty liver of above factors under ROC curve is 23. 2 Kg/m~2,63.7Kg, 1.32 mmol/L, 17.5 IU/L, 0.68 mmol/L and 22.5 IU/L, respectively.Conclusion1. The BMI is the factor which relates with fatty liver disease and possess the discriminat significance between fatty liver disease and non-fatty liver disease . Sometimes, the BMI is a factor that area under ROC curve is the biggest and that the sensitivity and specificity to the diagnosis of fatty liver disease is the best in all risks factors of fatty liver disease. The BMI is the important factor to diagnose the fatty liver disease. The 23.9Kg/m~2 and 23.2kg/m~2 is the diagnostic point of BMI to the fatty liver and the tendency of fatty liver, which may make a preliminary diagnosis for the fatty liver and the tendency of fatty liver, and which should are concened by the doctors.2. The questionaire table about the the relation both BMI and fatty liver is a diagnostic table for the fatty liver diasese which is convenient, effective, easy to be mastered by the doctors and be accepted by the patients. Using the questionaire table, we may make a preliminary diagnosis for the fatty liver diasease fast.