Predicting fetal lung maturity and assessing the risk of developing neonatal respiratory distress syndrome, when performed from 32 to 39 weeks gestation
Impedance
Fetal Lung Maturity
Amniotic Fld
Container/Tube: Amniotic fluid container or plastic vial
Specimen Volume: 2 mL
Collection Instructions:
1. Do not centrifuge
2. Amniotic specimens must be free of blood and meconium contamination.
0.75 mL
Gross hemolysis | Reject |
Centrifuged specimen Presence of blood or meconium | Reject |
Specimen Type | Temperature | Time | Special Container |
---|---|---|---|
Amniotic Fld | Refrigerated (preferred) | 28 days | |
Ambient | 7 days |
Predicting fetal lung maturity and assessing the risk of developing neonatal respiratory distress syndrome, when performed from 32 to 39 weeks gestation
Fetal lung maturity testing is used to determine the risk for developing respiratory distress syndrome (RDS) in infants born prematurely (32-39 weeks). The risk for developing RDS is inversely related to gestational age and is the most common cause of respiratory failure in neonates. RDS is associated with preterm birth due to insufficient production of pulmonary surfactant. Pulmonary surfactant is synthesized by type II pneumocytes. Surfactant consists of 90% phospholipids (primarily phosphatidylcholine and phosphatidylglycerol) and 10% proteins (surfactant proteins [SP]-A, SP-B, SP-C). Surfactant is packaged into lamellar bodies and is excreted into the alveolar space where it unravels and forms a monolayer on alveolar surfaces. Lamellar bodies can also pass into the amniotic cavity and, hence, are found in amniotic fluid. The surfactant functions to reduce the surface tension in the alveoli, preventing atelectasis. When surfactant is deficient, the small alveoli collapse and the large alveoli become overinflated and stiff, which has been associated with increased risk of developing respiratory distress. The status of fetal lung maturity is reflected in the concentration of surfactant in the form of phospholipids and lamellar bodies present in amniotic fluid. Lamellar bodies are similar in size to platelets and can be quantified on a hematology analyzer utilizing the platelet channel and used to estimate fetal lung maturity.
Immature: <15,000/mcL
Indeterminate: 15,000-50,000/mcL
Mature: >50,000/mcL
Cutoffs are based on consensus protocol (Neerhof M, Dohnal JC, Ashwood ER, et al: Lamellar body counts: a consensus on protocol. Obstet Gynecol. 2001;97:318-320)
Amniotic fluid lamellar body counts (LBC) above 50,000/mcL are predictive of fetal lung maturity.
Amniotic fluid LBC below 15,000/mcL are suggestive of fetal lung immaturity and increased risk of neonatal respiratory distress syndrome (RDS).
The main value of fetal lung maturity testing is predicting the absence of RDS. An immature test result for fetal lung maturity is less reliable in predicting the presence of RDS.(1)
Surfactant secretion into the amniotic fluid is minimal prior to 32 weeks gestation.
Fetal lung maturity testing is not indicated beyond week 39.
Specimens must not be frozen or centrifuged. Freezing and centrifuging the amniotic fluid falsely decreases the lamellar body count.
1. Fetal Lung Maturity: ACOG Practice bulletin. Obstet Gynecol. 2008;112(3):717-726
2. Eby C, Lu J, Gronowski AM: Lamellar body counts performed on automated hematology analyzers to assess fetal lung maturity. Lab Med. 2008;39(7):15
3. Haymond S, Luzzi V, Parvin C, Gronowski A: A direct comparison between lamellar body counts and fluorescent polarization methods for predicting respiratory distress syndrome. Am J Clin Pathol. 2006;126:894-899
4. Szallasi A, Gronowski A, Eby C: Lamellar body count in amniotic fluid: a comparative study of four different hematology analyzers. Clin Chem. 2003;49(6):994-997
5. Grenache DG, Gronowski AM: Fetal lung maturity. Clin Biochem. 2006;39:1-10
6. Neerhof M, Dohnal JC, Ashwood ER, et al: Lamellar body counts: a consensus on protocol. Obstet Gynecol. 2001;97:318-320
7. Kamath-Rayne BD, Jobe AH: Fetal lung development and surfactant. In: Resnik R ed. Creasy and Resnik's Maternal-Fetal Medicine: Principles and Practice. 8th ed. Elsevier; 2019:223-234
The Sysmex Automated Hematology Analyzer XN-9000 measures platelet count by the impedance method to quantify lamellar body counts.(Instruction manual: Automated Hematology Analyzer/Transportation units XN series [XN-9000] Instructions for Use [North American Edition]. Sysmex Corporation; 02/2014)
Monday through Sunday
This test was developed, and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the US Food and Drug Administration.
83664
Test Id | Test Order Name | Order LOINC Value |
---|---|---|
LBC | Lamellar Body Count, AF | 19114-8 |
Result Id | Test Result Name |
Result LOINC Value
Applies only to results expressed in units of measure originally reported by the performing laboratory. These values do not apply to results that are converted to other units of measure.
|
---|---|---|
LBCC | Lamellar Body Count | 19114-8 |
LBCI | Interpretation | 59462-2 |