Urinalysis and Body Fluids 6th Edition by Majorie DiLorenzo, Susan Strasinger

Exercise 4

Discuss the principle of and sources of error for the L/S ratio, Amniostat-FLM, lamellar body count, and Foam Stability Index for FLM.

Step 1 of 4

Principle and source of error in Lecithin-Sphingomyelin (L/S) Ratio:

The Lecithin-Sphingomyelin ratio is the reference method used to compare the tests of FLM (Fetal Lung Maturity).

• The primary component of the surfactants (combination of phospholipids, proteins and neutral lipids) is the lecithin ,which is helpful for stability of alveoli present in lungs

• Lecithin is produced constantly at low rate until 35^th week of gestation

• Sphingomyelin is a lipid produced constantly at low rate until 26^th week of gestation

• Both sphingomyelin and lecithin appears in amniotic fluid proportional to their concentrations in fetus

• After 35 weeks’ of gestation, lecithin production is elevated whereas concentration of sphingomyelin remains constant

• The meconium or blood in the fluid caused by contamination produces falsely elevated results (false positive result) because both blood and meconium contains sphingomyelin and lecithin.