Our results reveal ASGPR sH2a as a novel non-invasive marker for liver fibrosis and function. SH2a, the enzymes ALT, AST, GGT and ECM components like collagen and hyaluronic acid (HA) reflect different stages of the fibrogenic process. Hepatocytes are targets for most insults to the liver, including hepatitis viruses and alcohol 
. The damage caused abrogates the function of the hepatocytes and leads to subsequent release of inflammatory factors that activate hepatic stellate cells and cause them to differentiate to myofibroblasts that secrete ECM components and matrix metalloproteinases that degrade them 
. The secreted ECM components and their degradation products accumulate, originating fibrosis that further impairs liver function and develops to cirrhosis (). Thus, in the chain of events that leads to fibrogenesis, HA is a late indicator of the production of ECM; the enzymes are released by damaged cells; whereas we suggest that sH2a is a marker of liver function, correlating to the mass of functional hepatocytes (). Reduction of the levels of sH2a would reflect early events in the fibrogenic process, affecting hepatocyte function. We can speculate that the few cases where sH2a levels were abnormally high might indicate the start of a neoplastic process with proliferation of hepatocytes that express high levels of the ASGPR. At later tumorigenic stages, with dedifferentiation, one would expect again very low levels of sH2a. This is a subject that requires further studies. On the other hand, during the development of fibrosis, temporary changes in the total hepatocyte function (indicated by sH2a levels) may not occur simultaneously with changes in the release and clearance of damage markers (e.g. ALT). The function (sH2a) and damage markers give complementary information and when combined provide an accurate prediction of the fibrosis stage, including early and intermediate stages of fibrosis that other markers fail to detect. In our combined algorithm, the higher weight given to sH2a reduces the influence of ALT increases due to non-hepatic sources. SH2a is liver-specific, but we still do not know whether its blood levels are modulated or not in other diseases, for example in kidney disease, which could be a potential limitation.
Model depicting the sequence of events in the fibrogenic process and changes in sH2a secretion.
HA, as well as other proposed tests, can only differentiate very mild from very severe disease (
and our unpublished results). With our sH2a, ALT combination score a cutoff <4 gives a negative predictive value for fibrosis <2 of 92.9% and a positive predictive value for fibrosis >
2 of 62.1%. This fairs very well even when comparing with the predictive value of other markers for severe disease. For example, in one study a 60 µg/l HA cutoff gave a high negative predictive value (99.5%), for the absence of cirrhosis but very low positive predictive value in predicting cirrhosis (30%) 
. This was improved by combination of the levels of HA with those of AST and albumin, which gave a good prediction for absence of severe fibrosis but unsatisfactory for intermediate levels 
. Similarly, a better known combination method, Fibrotest, is useful for detecting advanced fibrosis but not very satisfactory at intermediate levels 
. It has been argued that biopsy itself has only an 80% accuracy 
. The simple combination of sH2a and ALT gave an AUROC of 0.786 for intermediate fibrosis (stages 2–3), which is better than other markers or combinations of markers. For advanced fibrosis and cirrhosis (stages 3–4) the AUROC obtained was 0.863, which compares very favorably with the AUROC obtained for severe disease with combinations of other markers, e.g. AUROC
0.76 for significant fibrosis and AUROC
0.82 for cirrhosis in an AST to platelet ratio 
0.81 for cirrhosis with combined HA, TIMP-1, and platelet count 
0.84 with Fibrotest 
A method that is being increasingly used is transient elastography (FibroScan), which measures liver stiffness, which in turn is correlated to fibrosis stage. Using this method the AUROC values obtained for significant fibrosis ranged from 0.76 to 0.83, quite suitable but lower than with the combination of sH2a with ALT 
. Like in other methods, the values that transient elastography provides for moderate fibrosis are not satisfactory; for example in one recent study it could not statistically differentiate stage 2 from 0–1 
. In addition, transient elastography values are inaccurate in obese patients or in those with fatty liver and the method cannot be used in patients with ascites.
The sensitive assessment of hepatocyte function by sH2a could allow the measuring of success of patient treatment. In a longitudinal study during treatment of HCV patients, the change in sH2a levels correlated, unlike other markers, with the success of the therapy (our unpublished results). Studies of membrane ASGPR levels upon resection and recovery or in liver transplantation suggest that sH2a could also be measured to monitor these interventions 
SH2a should be further evaluated as it emerges as a good candidate for a suitable liver fibrosis marker. It has been argued that such a marker should: be specific for the liver, be readily available, not be subject to false positive results, identify the stage of fibrosis