Determining a cutoff for fetal lung maturity with lamellar body count testing.

OBJECTIVE

A lamellar body count (LBC) >or= 50,000/microl is suggested to document fetal lung maturity (FLM). We sought to determine the LBC threshold for FLM with the Cell-dyn 4000 hematology analyser.

METHODS

We queried our database for patients who underwent LBC testing from 2001 to 2007. Included were deliveries between 35 and 38 weeks gestation with testing <or=7 days from delivery. We excluded twins, anomalies and cases of ruptured membranes. Data were analysed for sensitivity and specificity of predicting respiratory distress syndrome (RDS) and plotted on a receiver operating characteristic curve.

RESULTS

There were 209 patients meeting study criteria. Of these, 120 had diabetes. Five neonates experienced RDS, all born to non-diabetic mothers with LBC values <or=72,000/microl. At this value the sensitivity is 100%, false positive rate 18% and the p value is 0.0146.

CONCLUSION

Our results question the 50,000/microl threshold and demonstrate the need for hematology analyser specific thresholds.