Lamellar bodies are secreted by type II pneumocytes of the fetal lung and are surfactant rich. These bodies increase as the fetus matures and cause the increasing turbidity seen in the fluid. These bodies have a volume of 2-20 femtoliters, which is the volume measured in automated platelet analyzers.


Specimen: Amniotic fluid, protected from light.


Centrifugation reduces the counts by about 8%, does not improve the precision of the assay, and slows testing.


Testing: Platelet channel on an automated hematology analyzer.



• The counts increase exponentially after 28-30 weeks of gestation.

Count (particles per µL)


>= 55,000 centrifuged

(>= 60,000 uncentrifuged)

definitely mature, with no cases of respiratory distress seen

30,000 to 55,000

mature but rare cases of respiratory distress can occur

15,000 to 30,000

occasional cases of respiratory distress

< 15,000

immature and associated with high frequency of respiratory distress


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