Lamellar body number density and the prediction of respiratory distress

The determination of amniotic fluid lamellar body number density (LBND) has recently been shown to correlate well with other established indicators of fetal lung maturity. The authors have compared the LBND with a fetal lung phospholipid profile in predicting the clinical outcome in 52 well-documented cases. If a cutoff of 30,000/microL was used to indicate fetal lung maturity, there were no false-negative results for the LBND whereas there was one for the fetal lung profile. On the other hand, this cutoff resulted in 22 false-positive results for the LBND, whereas there were only 7 false-positive results by the fetal lung profile. The number of false-positive results by the LBND can be decreased by using a separate cutoff of less than 10,000/microL to indicate high risk for development of respiratory distress, while leaving the cutoff for predicting mature lung at 30,000/microL. This resulted in only four false-positive results for the LBND; each of these were from the same patients who also had false-positive results by the fetal lung profile. Care must be taken to ensure that the particle counter used is properly calibrated and that the appropriate cutoffs for both lung maturity and immaturity are used.