A Comprehensive Guide to the Scientific Diagnosis of Fatty Liver: From Risk Assessment and Blood Biochemistry to Imaging Grading Standards

Diagnostic methods for fatty liver include: 1. Presence of common risk factors, including obesity, diabetes, hyperlipidemia, alcoholism, and a history of medication use (commonly tetracycline, valerate, aspirin, glucocorticoids, synthetic estrogens, ketamine, nifedipine, methotrexate, certain antitumor drugs, and lipid-lowering drugs). 2. Serological examinations. Serum enzymes, β-globulin, ferritin, and bile acids are often elevated, while albumin, bilirubin, and prothrombin time (PT) are generally unchanged. Fatty liver may show varying degrees of elevation in serum indicators such as triglycerides, total cholesterol, and free fatty acids, especially elevated triglycerides, which has high diagnostic value clinically. 3. Liver function tests. For patients with moderate to severe fatty liver, liver function indicators can be of some reference value. Generally, abnormal serum bilirubin and varying degrees of elevation in ALT and AST are observed, which can help differentiate the type of fatty liver based on the degree of transaminase elevation.

Imaging examinations. (1) Ultrasound examination (B-scan) Imaging examinations can not only screen for fatty liver, but also confirm the diagnosis. Given that B-scan diagnosis of fatty liver has the advantages of being economical, rapid, and non-invasive, and that B-scan can detect fatty liver with a fat content of more than 30% and fatty liver with a fat content of more than 50%, the sensitivity of ultrasound diagnosis can reach 90%. Therefore, regular B-scan examinations of the liver for high-risk groups of fatty liver is the best way to detect fatty liver early. The so-called high-risk group of fatty liver refers to the group that has risk factors for the development of fatty liver and is more likely to develop fatty liver than the general population. Grading of fatty liver by B-scan examination: The characteristic change of fatty liver by B-scan examination is diffuse hyperechoic spots in the near field of the liver area (known as "bright liver"), attenuation of far field echoes in the liver area, sparse light spots, and at the same time, the branches of the hepatic vein and portal vein become thinner and narrower and are not clearly displayed. Alcoholic liver disease often presents with enlargement of the caudate lobe of the liver. This enlargement may be a characteristic change of alcoholic liver disease. In about 25% to 30% of patients with alcoholic liver disease, the caudate lobe is enlarged beyond the midline of the abdomen. In a few patients, the enlargement of the caudate lobe is so significant that it reaches nearly 1/3 of the entire liver.

Normal liver size values: maximum oblique diameter of the right lobe of the liver: not exceeding 12-14cm; anteroposterior diameter of the right lobe of the liver: not exceeding 8-10cm; thickness and length of the left half of the liver: thickness not exceeding 5-6cm, length not exceeding 5-9cm; length and thickness of the caudate lobe of the liver: not exceeding 4.5cm. Hepatologists have summarized the abnormal ultrasound manifestations of fatty liver into the following five aspects, and have formulated a graded standard for the severity of fatty liver by ultrasound based on the above manifestations. This standard is also applicable to patients with alcoholic liver disease. ① Diffuse enhancement of near-field echoes in the liver area, stronger than those in the kidneys and spleen, with gradual attenuation of far-field echoes. ② Intrahepatic ductal structures are not clearly displayed. ④ Intrahepatic color blood flow signals are reduced or difficult to display, but the direction of intrahepatic blood vessels is normal. ⑤ The echoes of the capsule and diaphragm of the right lobe of the liver are not clearly displayed or are incomplete. Mild fatty liver: having one of the above (1) to (4). Moderate fatty liver: having two of the above (1) to (4). Severe fatty liver: Having two of the above (1) to (4) and (5).

(2) CT. Diffuse fatty liver is characterized by a liver density (CT value) that is generally lower than that of the spleen, kidneys, and intrahepatic vessels. After enhancement, the intrahepatic vascular shadows are clearly visible, and their morphology and orientation are normal. The CT value is significantly negatively correlated with the amount of fat deposition in the liver. Since the CT value of the spleen is often relatively fixed, the liver/spleen CT value ratio can be used as a reference standard for measuring the degree of fatty liver or as a basis for treatment. CT has advantages in the diagnosis of fatty liver, and its accuracy is better than that of B-ultrasound, but its high cost and radiation are its disadvantages. CT manifestations and grading of fatty liver: Research data shows that there is a negative correlation between the size of the liver CT value and the liver fat content, that is, the more liver fat content, the smaller the liver CT value. Therefore, the severity of fatty liver can be understood based on the size of the liver CT value. CT shows that the density of a normal liver is uniform, with a CT value of 45-65 HU. Some studies suggest that the CT value for mild fatty liver is 40-50 HU, for moderate fatty liver it is 20-40 HU, and for severe fatty liver it is generally below -20 HU. Foreign scholars, combining CT scan results of the liver, spleen, and intrahepatic vessels, have proposed a CT plain scan grading standard for the severity of fatty liver: ① Mild fatty liver: Liver CT value is lower than spleen, but higher than intrahepatic vessels. ② Moderate fatty liver: Liver CT value is significantly lower than spleen; liver density is roughly the same as intrahepatic vessel density, with hepatic vessels being obscured, and their CT values ​​are essentially equal. ③ Severe fatty liver: Liver CT value is significantly decreased, intrahepatic vessel density is significantly increased, and liver CT value is lower than intrahepatic vessels, a condition medically known as hepatic vascular reversal.

The Fatty Liver and Alcoholic Liver Disease Group of the Hepatology Branch of the Chinese Medical Association has developed a grading standard for the severity of fatty liver based on the ratio of liver to spleen CT values. ① Mild fatty liver: 0.7 < liver/spleen CT ratio ≤ 1.0. ② Moderate fatty liver: 0.5 < liver/spleen CT ratio ≤ 0.7. ③ Severe fatty liver: liver/spleen CT ratio ≤ 0.5. This standard quantifies the severity of fatty liver by using the ratio of liver to spleen CT values, making it a simple, objective, and unified standard that is easy for CT examination physicians to understand and apply. 5. Liver biopsy. In recent years, the prevalence of non-alcoholic fatty liver disease has been gradually increasing. Currently, the proportion of white-collar workers diagnosed with fatty liver has reached over 20%, and there is a trend towards younger ages affected. However, many misconceptions still exist regarding fatty liver, and some effective prevention and treatment methods have not yet been well implemented.

From the survey data above, we can clearly see that although fatty liver disease is widespread, its scale is no less than that of cardiovascular and cerebrovascular diseases, yet people's understanding and awareness of it are surprisingly superficial. The main reasons for this are that fatty liver is often asymptomatic and asymptomatic, and people lack sufficient understanding of its dangers.