Diagnostic accuracy evaluation using ROC curve analysis.

The diagnostic accuracy of a biochemical quantity is inversely related to the overlapping zone between the values of the population suffering from a disease and the population which does not. The ROC curves are an indirect measure of the overlapping zone between both populations. Specimens (plasma and urine) taken from 928 patients with symptoms of acute abdominal pain were used and the catalytic concentration of alpha-amylase, pancreatic alpha-amylase and triacylglycerol lipase (determined by two methods) were measured. Definitive diagnosis was obtained by following the directives of expert groups on the evaluation of diagnostic tests. Diagnostic accuracy was characterized by calculating the diagnostic sensitivity and specificity, by representing the ROC curves and by quantifying the areas under the ROC curves. The catalytic concentration of pancreatic alpha-amylase in plasma was the quantity with a greater area under the ROC curve (A = 0.9740) and then the one which had greatest diagnostic accuracy. If we considered the upper limit of the reference interval to be the cut-off value, the catalytic concentration of pancreatic alpha-amylase in plasma had a diagnostic sensitivity and specificity values of 0.96 and 0.88 respectively for the acute pancreatitis.