Laboratory tests, often known as liver function tests (LFTs), are useful in the evaluation and treatment of patients with hepatic dysfunction, comprising serum aspartate and alanine transaminases, alkaline phosphatase, bilirubin and albumin. These tests often reveal abnormal results in patients with clinical problems other than liver dysfunction (1). Tests of the biosynthetic capacity of the liver include serum albumin, ceruloplasmin, ferritin, α1-antitrypsin, lipoproteins and blood-clotting factors. These substances are synthesized in the liver for transport into the circulation. Cholinesterase is synthesized mainly in hepatocytes and is released into the blood (2). Serum cholinesterase activity is reduced in liver dysfunction due to reduced synthesis. This is in contrast to other serum enzymes associated with the clinical assessment of liver function whose activities increase as a result of enhanced release from their cellular sources following cell membrane damage (3).

In gastroenterology, the Child-Pugh score (also known as the Child-Turcotte-Pugh score) is used to assess the prognosis of chronic liver disease, mainly cirrhosis. Although originally used to predict mortality during surgery, the Child-Pugh score is now used to determine the prognosis as well as the required strength of treatment, and the necessity for liver transplantation. As two main clinical measures in Child-Pugh score, serum protein and blood-clotting factors are important in evaluating the liver reserve function of cirrhotic patients (4). However, the cirrhotic patients, particularly those with Child grades B and C with ascites or hemorrhagic tendency, are usually treated with albumin or blood transfusion, which may affect the real numerical value for calculating the Child-Pugh score (5). Additionally, serum cholinesterase is not easily affected by this treatment. We therefore compared serum cholinesterase with the Child-Pugh score to evaluate the liver reserve function of cirrhotic patients. Moreover, since serum cholinesterase, albumin and blood-clotting factors are synthesized by the liver with different half-life (6), we also monitored the correction between cholinesterase, albumin and serum plasma prothrombin time.

In biochemistry, cholinesterase is a family of enzymes that catalyzes the hydrolysis of the neurotransmitter acetylcholine into choline and acetic acid, a reaction necessary to allow a cholinergic neuron to return to its resting state after activation (8). There are two types of cholinesterases acetylcholinesterase (AchE), also known as RBC and erythrocyte cholinesterases or acetylcholine acetylhydrolase, found primarily in the blood and neural synapses. AchE exists in various molecular forms. In the mammalian brain the majority of AchE occurs as a tetrameric, G4 form with much smaller amounts of a monomeric G1 form (9). Pseudocholinesterase, also termed plasma cholinesterase, butyrylcholinesterase or acylcholine acylhydrolase, is found primarily in the liver (10,11).

Estimation of the level of activity of the cholinesterase found in serum was first suggested by McArdle (1940)(12), as a useful means for differentiating hepatic from post-hepatic jaundice. The evidence which has accumulated suggests that cholinesterase activity is an assessment indicator for liver function in patients with liver disease. In China, cholinesterase has been included in scores to distinguish hepatitis severity by society of liver disease (7). However, few studies are available regarding the value of cholinesterase in evaluating liver reserve function of cirrhotic patients. The Child-Turcotte-Pugh scoring system is the first of its kind in stratifying the seriousness of end-stage liver disease, mainly cirrhosis (13). In our study, 866 cirrhotic patients were strictly grouped into A, B and C grades, as per their Child-Pugh score. The results show that cholinesterase tended to significantly decrease in the three grades: Child A (5368.04±1657.32 U/l), Child B (2943.06±1212.84 U/l) and Child C (1832.51±710.68 U/l). This result is in agreement with the findings of Gu and Zhong (14). Their data demonstrated that cholinesterase in the three grades were: Child A (5978±535 U/l), Child B (3957±454 U/l) and Child C (2267±332 U/l). The Child-Pugh score employs five clinical measures of liver disease, among which ascites and hepatic encephalopathy are subjective measures (15). Liver cirrhosis is classified into Child-Pugh class A–C, employing the added score from above. Compared with the Child-Pugh score, cholinesterase is easier and more objective in evaluating the liver reserve function of cirrhotic patients.

The liver performs an important role in biosynthesis. Cholinesterase, albumin and blood-clotting factors are synthesized in the liver to be transported into the circulation. Thus, LFTs include cholinesterase, albumin and prothrombin time and may provide useful information concerning the state of a cirrhotic patient’s liver. In our study, in cirrhotic patients, cholinesterase was positively correlated with albumin and negatively correlated with plasma prothrombin time, confirming that those substances were synthesized in the liver and reduced in liver dysfunction due to reduced synthesis. In decompensated cirrhotic patients, albumin or blood transfusion are usually used, which may affect the real numerical value to calculate the Child-Pugh score (16). If surgery is selected as the method of treatment based on the effected Child-Pugh scores, the risk for liver failure is likely to increase (17). In their study, Gu and Zhong (14) demonstrated that three cirrhotic patients (two Child B- and one Child A-score patient) suffered hepatic encephalopathy following portal azygous disconnection operation, with cholinesterase levels of <2,000 U/l. Thus, those authors suggested that cirrhotic patients with cholinesterase of <2,000 U/l may have higher risk for liver failure, if undergoing abdominal surgery. Thus, the combination cholinesterase of and the Child-Pugh score may be more subjective and accurate in evaluating the liver reserve function of cirrhotic patients, which is useful for surgeons to decide on surgery timing.

In conclusion, findings of the present study have demonstrated that the level of cholinesterase is closely correlated with the damage severity of liver cells and may respond to the liver reserve function of cirrhotic patients. Compared with the Child-Pugh score, serum cholinesterase is less complex and not easily affected by treatments for decompensated cirrhosis. The combination of cholinesterase with the Child-Pugh score may be more subjective and accurate in evaluating the liver reserve function of cirrhotic patients.