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

Exercise 8

When performing an L/S ratio by thin-layer chromatography, a mature fetal lung will show:

A. Sphingomyelin twice as concentrated as lecithin

B. No sphingomyelin

C. Lecithin twice as concentrated as sphingomyelin

D. Equal concentrations of lecithin and sphingomyelin

Step 1 of 2

Lecithin-Sphingomyelin (L/S) ratio:

The Lecithin-Sphingomyelin ratio is the reference method that is utilized 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

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

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

• The ratio of L/S is less than 1.6 until the 35^th week of gestation, because only after gestation period of 35 weeks a noticeable increase in production of lecithin occurs, until then large amount of lecithin is not produced

• Both lecithin and sphingomyelin show up in the amniotic liquid in sums proportional to their concentration in the fetus

• When performing Lecithin-Sphingomyelin ratio using thin layer chromatography, the FLM shows lecithin is concentrated twice as sphingomyelin

• Because, after 35 weeks gestation, the lecithin concentration increases, whereas the sphingomyelin concentration remains constant.

Therefore, when performing Lecithin-Sphingomyelin ratio using thin layer chromatography, the FLM shows “lecithin is concentrated twice as sphingomyelin”. Hence, the correct answer is option.