IS FLUORESCENCE POLARIZATION RELIABLE AND COST-EFFICIENT IN A FETAL LUNG MATURITY CASCADE

OBJECTIVE: The objective of the study was to compare the accuracy of t he TDxFLM test (Abbott Laboratories) with the fetal lung maturity casc ade (shake, foam stability index, lecithin/sphingomyelin tests) and to determine whether the TDxFLM test could increase the efficiency and r educe the cost without decreasing the reliability of a cascade. STUDY DESIGN: A prospective, single-blinded study was conducted. Uncontamina ted amniotic fluid obtained by transabdominal amniocentesis for fetal lung maturity assessment was evaluated with use of the fetal lung matu rity cascade and the TDxFLM test. At study completion the results of t he TDxFLM test were compared with those of the maturity cascade with r egard to hyaline membrane disease, which was defined by strict clinica l and radiographic parameters. A power analysis was performed requirin g a sample size of 100 infants delivered within 72 hours of amniocente sis with use of the 95% confidence interval. RESULTS: A total of 115 c ases had a full maturity cascade performed, of which 40 (35%) had a po sitive shake or foam stability index and 75 cases required progression to a lecithin/sphingomyelin ratio because of negative results. The TD xFLM test result was greater than or equal to 70 mg/gm in 42 (37%) of these 115. One hundred eight newborns were delivered within 72 hours o f the amniocentesis; 65% (71) of these were between 30 and 37 weeks of estimated gestational age. There were 7 cases of hyaline membrane dis ease in the 108 newborns. Of these 108, 87 had a mature original casca de versus 85 mature tests with use of a proposed TDxFLM test-lecithin/ sphingomyelin ratio cascade with one case of respiratory distress synd rome and hyaline membrane disease. The sensitivity, specificity, and p ositive and negative predictive values for the original cascade were 8 6%, 84%, 27%, and 99%, respectively; for the proposed TDxFLM test-leci thin/sphingomyelin ratio cascade the values were 86%, 83%, 26%, and 99 %, respectively. The TDxFLM test-lecithin/sphingomyelin ratio cascade would have resulted in a cost reduction of 24% with no significant del ay in turnaround time. CONCLUSION: The TDxFLM test appears to be a rel iable and accurate assessment of fetal lung maturity. Furthermore, by replacing the shake and foam stability index portion of the cascade wi th the TDxFLM test, a cost savings of 24% would occur without a decrea se in safety. These results also reveal that it could enhance patient care and be cost efficient for institutions not currently doing fetal pulmonary maturity testing to undertake use of the TDxFLM test and to only send out specimens for a lecithin/sphingomyelin ratio that have a n initial immature TDxFLM test result (<70 mg/gm). Likewise, instituti ons currently only performing a lecithin/sphingomyelin ratio may consi der a TDxFLM test-lecithin sphingomyelin ratio cascade. Although direc t costs would increase, they would be counterbalanced by a significant reduction in laboratory technician time.