Lecithin:Sphingomyelin Ratio, Phosphatidyl Glycerol and Creatinine, Amniotic Fluid
| Lecithin:Sphingomyelin Ratio, Phosphatidyl Glycerol and Creatinine, Amniotic Fluid | | | |
| Number | | 092742 |
| CPT | | 82570; 83661; 84081 |
| Related Information | | Phosphatidylglycerol (PG) and Creatinine, Amniotic Fluid |
| Synonyms | | Creatinine, Amniotic Fluid ; Fetal Lung Maturity ; Glycerol ; L:S Ratio ; L:S With PG and Creatinine ; Phosphatidyl Glycerol |
| Test Includes | | Creatinine; L:S ratio; qualitative determination for the presence of PG |
Special Instructions | | Correlation of maternal serum and amniotic fluid creatinine
levels is recommended. For a complete test description, see
Lecithin:Sphingomyelin Ratio and
Phosphatidyl Glycerol, Amniotic Fluid [120527] . |
| Specimen | | Amniotic fluid, frozen |
| Volume | | 7 mL |
| Minimum Volume | | 3 mL |
| Container | | Plastic transport tube |
| Collection | | Amniocentesis. Send sample to the laboratory immediately after collection. Collections from tracheal or pharyngeal aspirates from newborns are acceptable. Samples collected vaginally are satisfactory only if care is taken to obtain a “clean” sample (void of blood or meconium), and should only be used if the fluid is free flowing and carefully tapped. To avoid delays in turnaround time when requesting multiple tests on frozen samples, please submit separate frozen specimens for each test requested. |
| Storage Instructions | | Record color and, if present, any mucus or heavy
precipitate. Immediately after collection, centrifuge
specimen exactly for 3 minutes at 500xg in
centrifuge and transfer supernatant to a labeled tube.
Discard the original tube and pellet. No special
additives or preservatives are required. Send supernatant.
Freeze. |
| Aftercare | | Kleihauer should be done after amniocentesis on Rh negative patients. If abnormal result, some recommend Rh immune globulin (human). |
| Causes for Rejection | | Specimen contaminated with blood or meconium; repeated
freezing and thawing of specimen; specimen left at room
temperature for any length of time (>1 hour) |
| Reference Interval | | Creatinine: >2 mg/dL at 37th to 38th week; results >2 mg/dL indicate maturity if maternal serum creatinine is normal. Concentrations of 1.6-1.8 mg/dL are found at the 36th week. |
| Critical Values | | Creatinine in amniotic fluid <1.6 mg/dL bears an implication that the fetus is immature or premature,1 <2500 g. |
| Use | | Creatinine: Estimate fetal age in concert with other parameters. Creatinine of 2 mg/dL is an indication of maturity. |
| Limitations | | Creatinine: Oligohydramnios, related to fetal urinary tract obstruction or to renal agenesis, or polyhydramnios, may alter the usual amniotic fluid criteria set forth above.1 Elevation of maternal creatinine may cause increases in the amniotic fluid creatinine level. Complications of amniocentesis may occur. |
| Methodology | | L:S ratio: thin-layer chromatography (TLC); PG: immunologic agglutination; creatinine: spectrophotometry |
| Contraindications | | Fetal age must be estimated from more than a single facet. |
| Additional Information | | Creatinine: Fetal lung and kidney development are related, and normal lung development is dependent on the normal development of the kidneys. Estimation of fetal kidney maturity by measuring amniotic fluid creatinine, therefore, provides an indirect assessment of fetal lung maturity. |
| Footnotes | | - Dito WR, “Amniotic Fluid and Maternal Serum Assessment in Pregnancies at Risk,” Gradwohl's Clinical Laboratory Methods and Diagnosis, 8th ed, Sonnenwirth AC and Jarett L, eds, St Louis, MO: Mosby-Year Book Inc, 1980, 469-77
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