Establishment of reference values of five amniotic fluid enzymes. Analytical performances of the Hitachi 911. Application to complicated pregnancies

Objectives: to evaluate the analytical performances of the Hitachi 911 anal yzer (Roche Diagnostics, F) for gamma -glutamyl-transferase, 5 ' nucleotida se, amylase, asparate-amino-transferase and total-alkaline-phosphatase assa y in amniotic fluid. To establish reference intervals for these five enzyme s throughout gestation. To determine their antenatal diagnostic value. Design and methods: amniotic fluid samples were collected between 14 and 35 weeks of gestation. Weekly numbers ranged from 31 to 92. Techniques develo ped for serum enzyme assays were applied to amniotic fluid. Two pools of am niotic fluid containing low and high marker levels were used. Within-day an d between-day variations were calculated, together with the limits of detec tion and linearity. Reference ranges were established on 508 amniotic fluid samples, including 23 samples from pregnancies with chromosomal aberration s, 14 with gastrointestinal tract defects and 5 with gastroschisis. Results: the assay technique for total-alkaline-phosphatase assay had to be adapted to amniotic fluid, but no adaptation was necessary for the other m arkers. The within-day CV ranged between 2.2 and 11.2% for low-level sample s and from 1.1 to 3.4% for high-level samples. The between-day CV ranged fr om 6.3 to 13.3% for low-level samples and 1.2 to 4.7% for high-level sample s. Total-alkaline-phosphatase activity fluctuated throughout gestation. Amy lase levels and aspartate-amino-transferase levels increased whereas gamma -glutamyl-transferase and S'nucleotidase levels fell until delivery. All tr isomy 18 and trisomy 13 pregnancies, 65% of Down's syndrome pregnancies and all pregnancies with digestive tract defects were associated with marked c hanges in the level of at least one enzyme. Conclusion: The Hitachi 911 is suited to rapid, reliable quantification of amniotic fluid enzymes with only minor adaptation. Useful reference interva ls can be obtained throughout gestation. Gamma-glutamyl-transferase, S'nucl eotidase, total-alkaline-phosphatase and amylase assay can help to confirm echographic evidence of bowel disorders and thereby improve patient managem ent especially in case of gastroschisis. (C) 2001 The Canadian Society of C linical Chemists. All rights reserved.