Comparison of serum 7S fragment of type IV collagen and serum central triple-helix of type IV collagen for assessment of liver fibrosis in patients with chronic viral liver disease

A competitive radioimmunoassay for serum 7S fragment of type IV collagen (7S collagen) using a polyclonal antibody against 7S collagen and a sandwich enzyme immunoassay for serum central triple-helix of type IV collagen (IV collagen) using two monoclonal antibodies against the pepsin-solubilized type IV collagen may be used as diagnostic aids for liver fibrosis in clinical medicine. We compared the clinical usefulness for assessing liver fibrosis of serum 7S collagen and IV collagen tests in chronic viral liver diseases, and also examined the elution pattern of 7S collagen- and IV collagen-related antigens in serum by gel filtration analysis. Methods: Serum 7S collagen and IV collagen levels were assayed in 151 patients with chronic viral liver disease and 30 healthy control subjects. Results: Gel filtration on the Sephacryl S400HR column revealed that the 7S collagen antigenicity in serum was heterogeneous, whereas the IV collagen antigen in serum was uniform in size. Serum levels of 7S collagen and IV collagen showed increases closely correlated with the severity of liver disease. The abnormal percentage of 7S collagen in three patient groups was similar to that of IV collagen in the corresponding groups. Serum 7S collagen and IV collagen levels were strongly correlated with the histological degree of liver fibrosis; the correlation coefficients were R=+0.675 for 7S collagen and R=+0.665 for IV collagen. When we assessed the ability of each test to detect cirrhosis with a receiver operating curve, the serum 7S collagen test was a slightly better marker than the serum IV collagen test. For the detection of cirrhosis, serum 7S collagen was 83% sensitive and 88% specific at a cutoff value of 9 ng/ml, and serum IV collagen was 80% sensitive and 81% specific at a cutoff value of 160 ng/ml. Conclusions: These findings suggested that serum 7S collagen and IV collagen tests are similarly useful for assessing liver fibrosis in patients with chronic viral liver disease, although the former is slightly better for diagnosing cirrhosis than the latter.