The test most widely used to assess fetal lung maturity is going away. Earlier this year I wrote about the different laboratory tests that doctors use to determine if a fetus' lungs were mature. One of those tests, the surfactant-to-albumin ratio, is marketed and sold by Abbott Laboratories as the TDx FLM II test. Last year, they announced that they were discontinuing the manufacture of that test.
The main reason this test will no longer be made is that the instrument that performs the test is several decades old. The TDx line of instruments is aging and the technology it uses is becoming outdated. The decision to stop supporting the TDx makes sense but it does leave labs that offer the FLM II assay in a bit of a quandary. The Abbott test performs well and is rapid and simple to perform. Doctors are familiar with it and know how to interpret the results. The test is an excellent predictor of fetal lung maturity and the risk of respiratory distress syndrome as a function of both gestational age and TDx FLM II result is known. Labs that currently offer the TDx FLM II test and that wish to continue offering a test for fetal lung maturity have to figure out what to do. Doctors will also have to learn what the loss of this test will have on their clinical practice.
I recently published the results of a survey that provide some insight as to what might be expected. Here is a summary of those data:
- Across the US, labs are performing fewer fetal lung maturity tests each year and the most widely used test is Abbott's TDx FLM II test.
- Although 25% of physicians indicated that their use of fetal lung maturity tests is decreasing, 90% of them said that they could not provide their current level of care without access to a test of fetal lung maturity.
- Without the TDx FLM II test, 65% of physicians would order the lecithin-to-sphingomyelin (L/S) ratio and 40% would order the lamellar body count (LBC).
- Fewer than 20% of labs offer the L/S ratio and even fewer offer the LBC.
- Laboratories could simply refer fetal lung maturity test requests to a lab that performs other lung maturity tests but doctors want results within 12 hours of ordering the test. That expectation probably can't be realized if the test is not performed in the lab.
Of all the available tests that could potentially replace the TDx FLM II test, the LBC test is the most logical:
- The instrumentation required to perform the test is an automated cell counter and these are widely available in clinical labs.
- The test is performed rapidly and with high precision.
- Several outcome-based studies have demonstrated the diagnostic utility of the LBC and it performs as well as the TDx FLM II test.
When I'm asked by laboratorians what they should do when the TDx FLM II test goes away I tell them that they should consider the LBC test. Of all the other tests of fetal lung maturity, the LBC, for the reasons outlined above, is the most logical replacement test. I also caution them that time is running out and that NOW is the time to communicate with their physicians about the need for the change and to get their input.
It's worth re-stating that perhaps, just maybe, we could consider stop performing fetal lung maturity tests altogether. Time will tell.