Predictive values of serum [formula omitted] for fibrotic liver disorders — correlation with monoamine oxidase activity

Abstract

The determination of the activity of N- acetyl-β- d-glucosaminidase (NAG, EC 3.2.1.30) has been suggested as a valuable procedure to ascertain and monitor liver cirrhosis and fibrosis. In the present study the criteria of the diagnostic reliability of this enzyme, i.e. diagnostic specificity, sensitivity and positive and negative predictive values have been estimated by analysing the activity in sera of 87 healthy persons, 85 patients with histologically verified liver fibrosis and cirrhosis, 159 patients with various non-liver and non-fibrotic liver diseases and 21 patients with acute viral hepatitis. In comparison to enzyme activity (mean ± SD) in normal sera (21 ± 5 U/1) patients with chronic liver diseases have elevated NAG activities (mean activity between 34 and 40 U/1) but clear differences in the activities between the various groups could not be shown. 45 85 of liver cirrhotic and fibrotic subjects had pathologically elevated NAG activities (> 32 U/l), but so did 54 159 patients with various non-liver and non-fibrotic liver diseases excluding acute hepatitis. Diagnostic specificity improves with increasing cut-off values (activity above which the test result is pathologic), but this is inevitably accompanied by a loss of diagnostic sensitivity. The predictive values of NAG for cirrhosis and fibrosis are low even if tested against a reference population of healthy subjects. Assuming a prevalence of chronic liver diseases of 3.3%, NAG at a cut-off activity of 24 U/l has a positive predictive value of 9% and a negative predictive value of 99% with respect to a reference population of healthy persons. The values obtained do not indicate diagnostic importance for this enzyme for liver cirrhosis/fibrosis. The activity of NAG in sera of liver- and non-liver disease patients does not correlate statistically with that of monoamine oxidase (EC 1.4.3.4), another proposed indicator of liver cirrhosis and fibrosis. In contrast to the greatly elevated NAG activities in sera of patients with acute hepatitis, monoamine oxidase activities remain unaffected under conditions of liver cell necrosis. Monoamine oxidase proves to have a greater diagnostic specificity for fibroproliferative liver disorders than NAG; the latter enzyme, however, is more sensitive. Thus, the combined use of both enzymes in evaluating liver cirrhosis and fibrosis might be rational.