3.7　Indirect Tests

While all tests described above are direct tests based on the measurement of secreted enzymes and bicarbonate，indirect pancreatic function tests described below investigate secondary effects which are due to the lack of enzymes（Chowdhury and Forsmark 2003）.Among these，the fluorescein dilaurate（pancreolauryl test=PLT）and the NBTPABA test（N-benzoyl-L-tyrosyl-p-aminobenzoic acid test）were frequently used but are no longer commercially available in many countries.Briefly，for these tests，the patient ingests a substrate that is metabolized by pancreatic enzymes.At least one of the metabolites is absorbed from the gut，conjugated，and excreted in urine，where it can be measured.Increased fecal excretion of the substrate and decreased urinary excretion of the degraded metabolite suggests pancreatic exocrine insufficiency（Keller and Layer 2015）.To account for inter-individual variability of intestinal absorption and renal function，the fluorescein dilaurate test includes application of the absorbable metabolite（fluorescein）on a second day and the results of the test are expressed as the ratio of excreted fluorescein on the test and the control day in percent.A ratio of less than 20%is clearly abnormal（Keller and Layer 2015）.A modified serum test simplifies the procedure but does not increase sensitivity and specificity（Siegmund et al.2004）.(https://www.daowen.com)